Generics. (Lecture 7.3) презентация

What if you could say that your code works with "some unspecified type," rather than a specific interface or class?

Generics implement the concept of parameterized types, which allow multiple types.

A class that holds a single object
class Automobile {}
public class Holder1 {
private Automobile a;
public Holder1(Automobile a) {
this.a = a;
}
Automobile get() { return a; }
}

A class that holds an Object
public class Holder2 { private Object a; public Holder2(Object a) { this.a = a; } public void set(Object a) { this.a = a; } public Object get() { return a; } public static void main(String[] args) { Holder2 h2 = new Holder2(new Automobile()); Automobile a = (Automobile) h2.get(); h2.set("Not an Automobile"); String s = (String) h2.get(); h2.set(1); // Autoboxes to Integer Integer x = (Integer) h2.get(); }
}

Simple generic class
public class Holder3
{
private T a;
public Holder3(T a) { this.a = a; } public void set(T a) { this.a = a; } public T get() { return a; } public static void main(String[] args) { Holder3
h3 =
new Holder3
(new Automobile()); Automobile a = h3.get(); // No cast needed // h3.set("Not an Automobile"); // Error // h3.set(1); // Error }
}

Generic Types and Methods
There can be:
Generic classes
Generic interfaces
Generic methods
Bounded generic types
Generic wildcards

The core idea of Java generics: You tell it what type you want to use, and it takes care of the details.

Type erasure
Java generics are implemented using type erasure. This means that any specific type information is erased when you compile your code.

How type erasure works?
public class Holder3
{ private T a; public Holder3(T a) { this.a = a; } public void set(T a) { this.a = a; } public T get() { return a; }
}
…
Holder3
h3 =
new Holder3
(1L);
Long n = h3.get();
public class Holder3 { private Object a; public Holder3(Object a) { this.a = a; } public void set(Object a) { this.a = a; } public Object get() { return a; }
}
…
Holder3 h3 = new Holder3(1L);
Long n = (Long) h3.get();

Compensating for erasure
public class Erased
{
private final int SIZE = 100;
public static void f(Object arg) {
if(arg instanceof T) {} // Error
T var = new T(); // Error
T[] array = new T[SIZE]; // Error
T[] array = (T[])new Object[SIZE]; // Unchecked warning
}
}

Generic class with two types
public class TwoTuple
{ public final A first; public final B second; public TwoTuple(A a, B b) { first = a; second = b; } public String toString() { return "(" + first + ", " + second + ")"; }
}

You cannot use primitives as type parameters!
TwoTuple
ttsi = new TwoTuple
("hi", 47);
but not
TwoTuple
ttdi = new TwoTuple
(47.0, 47);

Inheritance with generic classes
public class ThreeTuple
extends TwoTuple
{ public final C third; public ThreeTuple(A a, B b, C c) { super(a, b); third = c; } public String toString() { return "(" + first + ", " + second + ", " +
third +")"; }
}

Generic interface
public interface Generator
{ T next(); }
public class Fibonacci implements Generator
{ private int count = 0;
public Integer next() { return fib(count++); }
...
public static void main(String[] args) {
Fibonacci gen = new Fibonacci();
for(int i = 0; i < 18; i++)
System.out.print(gen.next() + " ");
}
}

Generic Methods
public class GenericMethods {
public
void f(T x) {
System.out.println(x.getClass().getName());
} public static void main(String[] args) {
GenericMethods gm = new GenericMethods();
gm.f("");
gm.f(1);
gm.f(1.0);
gm.f('c');
gm.f(new String[] {“H”, “W”});
}
}

The Syntax for Invoking a Generic Method
Generics have an optional syntax for specifying the type for a generic method. You can place the data type of the generic in angle brackets, < > , after the dot operator and before the method call.
gm.
f(“a string object”);
gm.
f(1);
gm.
f(1.0);
gm.
f('c');
gm.
f(new String[] {“H”, “W”});
The syntax makes the code more readable and also gives you control over the generic type in situations where the type might not be obvious.

Leveraging type argument inference
public class Tuple {
public static
TwoTuple
tuple(A a, B b) {
return new TwoTuple
(a, b);
}
public static
ThreeTuple
tuple(A a,B b,C c) {
return new ThreeTuple
(a, b, c);
}
}
...
TwoTuple
ttsi = Tuple.tuple(“hi”, 47);
ThreeTuple
ttsid=Tuple.tuple(“hi”,47,47.0);

Anonymous inner classes
public interface Generator
{ T next(); }
class Customer { private Customer() {} public static Generator
generator() { return new Generator
() { public Customer next() { return new Customer(); } }; }
}
...
Customer customer1 = Customer.generator().next();
Customer customer2 = Customer.generator().next();

Bounded Generic Types
Because erasure removes type information, the only methods you can call for an unbounded generic parameter are those available for Object. Bounds allow you to place constraints on the parameter types. Important effect is that you can call methods that are in your bound types.
interface HasColor {
Color getColor();
}
class Colored
{
T item;
public Colored(T item) { this.item = item; }
public T getItem() { return item; }
// The bound allows you to call a method:
public Color color() { return item.getColor(); }
}

Compound bounds
class Dimension { public int x, y, z; }
// Multiple bounds:
class ColoredDimension
{ T item; ColoredDimension(T item) { this.item = item; } T getItem() { return item; } Color color() { return item.getColor(); } int getX() { return item.x; } int getY() { return item.y; } int getZ() { return item.z; }
}

Bounds and Inheritance
class HoldItem
{
T item;
HoldItem(T item) { this.item = item; }
T getItem() { return item; }
}
class Colored2
extends HoldItem
{ // some code here...
Color color() { return item.getColor(); }
}
class ColoredDimension2
extends Colored2
{
// some code here...
int getX() { return item.x; } int getY() { return item.y; } int getZ() { return item.z; }
}

Polymorphism and Generics
class Holder
{
T item;
void set(T item) { this.item = item; }
T get() { return item; }
}
abstract class Parent { }
class Child extends Parent { }
class AnotherChild extends Parent { }
...
Holder
h1 = new Holder
(); // OK
Holder
h2 = new Holder
(); // OK
Holder
h3 = new Holder
(); // Error
// because one could do this:
// h3.set(new AnotherChild());

Why Polymorphism doesn’t work
class Holder
{
T[] items;
int num = 0;
void add(T item) { this.items[num++] = item;}
T[] get() { return items; }
}
...
Holder
h = new Holder
();
h.add(1);
h.add(2);
Holder
reg = h;
h.add(new Double(1.25));
Integer i3 = h.get()[2]
So Double is a Number but Holder
is not Holder
Class case exception Double != Integer
h -> {Integer, Integer, Double}
If polymorphism was allowed this would be legal
This is also legal since Double is a Number

But you can do this:
This is how you can put different object types in parameterized Holder object:
Holder
h = new Holder
();
h.add(1);
h.add(2);
h.add(new Double(1.25));
Number i3 = h.get()[2]
Both Integer and Double are the Numbers

More Example
abstract class Animal { public abstract void check(); }
class Dog extends Animal {
public void check() { S.o.p("Dog"); }
}
class Cat extends Animal {
public void check() { S.o.p("Cat"); }
}
class AnimalDoctor {
void checkAnimal(Holder
animal) {
animal.get().check();
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
cat = new Holder
();
AnimalDoctor doctor = new AnimalDoctor();
doctor.checkAnimal(dog); // Error
doctor.checkAnimal(cat); // Error
}
}

Generic Wildcards (?)
The wildcard provides a polymorphic - like behavior for declaring generics. , an unbounded wildcard
, a wildcard with an upper bound
, a wildcard with a lower bound

Unbounded Wildcards
The unbounded wildcard represents any data type, similar to the < T > syntax.
public static void printList(List
list) {
for(Object x : list) {
System.out.println(x.toString());
}
}
...
ArrayList
keywords = new ArrayList
();
kyewords.add(“generic”);
printList(keywords);
Use the ? in situations where you do not need a formal parameter type like < T >
Data type is not required here

Be careful
Holder
h = new Holder
();
h.add(new Object()); // compile time error
h.add(new String()); // compile time error
// one exception!
h.add(null); // null is member of every type
Working with unbounded wildcards we can only read data, not assign!

Upper - Bound Wildcards
Bounded wildcards put some restrictions on unknown type:
public static void printList(List
list){
for(Number x : list) {
System.out.println(x.doubleValue());
}
list.add(new Integer(3)); // compile error
}
Now we know that object is instance of Number
But we still don’t know exact type, so can’t modify list

More example
class AnimalDoctor {
void checkAnimal(Holder
animal) {
animal.get().check(); // OK animal.set(new Cat()); // Error: we don’t know exact parameter type of animal
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
cat = new Holder
();
AnimalDoctor doctor = new AnimalDoctor();
doctor.checkAnimal(dog); // OK
doctor.checkAnimal(cat); // OK
}
}

Lower Bounded Wildcards
a lower bounded wildcard restricts the unknown type to be a specific type or a super type of that type
Holder
h = new Holder
();
h.add(new Integer(1));
Integer i1 = h.get(); // compilation error
// get returns Object
Integer i2 = (Integer)h.get(); // OK
Lower bounded wildcards allow to modify but not read!!

Example
public static void addNumbers(List
list) {
for (int i = 1; i <= 10; i++) {
list.add(i);
}
}
List
i = new ArrayList
();
List
n = new ArrayList
();
List
o = new ArrayList
();
addNumbers(i);
addNumbers(n);
addNumbers(o);
This works fine
Слайд 34
More example
class AnimalDoctor {
void checkAnimal(Holder
dog) {
animal.get().check(); // Error!
// get() returns Object ref
animal.set(new Dog()); // OK
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
animal = new Holder
();
Holder
cat= new Holder
();
AnimalDoctor doctor = new AnimalDoctor();
doctor.checkAnimal(dog); // OK
doctor.checkAnimal(animal); // OK
doctor.checkAnimal(cat); //Error: Cat isn’t super of Dog
}
}
Слайд 35
What's the difference?
void check(Holder
holder) { }
void check(Holder
holder) { }
Слайд 36
There IS a huge difference!
class Main {
void check(Holder
obj) {
obj.set(new Dog());
obj.set(new Cat());
}
public static void main(String[] args) {
Holder
obj = new Holder
();
Main main = new Main();
main.check(obj); // Only Holder
goes here!
}
}
Слайд 37
There IS a huge difference!
class Main {
void check(Holder
obj) {
obj.set(new Dog());
// Error
// Compiler isn't sure that it's really Dog Holder
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
integer = new Holder
();
Main main = new Main();
main.check(dog); // OK
main.check(integer); // OK
}
}
Слайд 38
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 39
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 40
Naming Conventions for Generics
E for an element
K for a map key
V for a
map value
N for a number
T for a generic data type
Use S , U , V , and so on for multiple types in the same class.
Слайд 41
Summary
1) Generics let you enforce compile-time type safety.
Holder
h1 = new Holder
();
Holder h2 =
new Holder();
String s = h1.get(); // no cast needed
String s = (String) h2.get(); // cast required
2) Generic type information does not exist at runtime — it is for compile-time safety only.
3) Polymorphic assignment don't apply to the generic type
Holder
h1 = new Holder
(); // Error
4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:
void foo(List
d) {} // can take only
void foo(List
) {} // take a
or
void foo(List
) {} // take a
or
5) When using a wildcard, List
, the collection can be accessed but not modified.
Имя файла: Generics.-(Lecture-7.3).pptx
Количество просмотров: 144
Количество скачиваний: 0
Скачать
- Предыдущая
Internet technologies
Следующая -
Трагедия Гёте Фауст
Похожие презентации
Научно-техническая информация
Презентация к аттестации учителя информатики
Основные компоненты ПК
Арифметические основы организации ЭВМ
Вёрстка и дизайн газетной статьи
Алгоритм действий родителей для прохождения регистрации их детей младше/старше 14 лет во ФГИС Моя школа
Керування правами доступу
Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)
Взаимодействие клиента и сервера
Как с нуля запустить Онлайн-школу
Программа Project Expert
What is cryptocurrency
История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД
WORD-тын графикалык мумкіндіктері
Компьютер как универсальное устройство обработки информации
Линейное программирование
ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области
Социальная память. Функция социальной памяти
Різновиди діаграм та їх форматування
Лекция 2. Файлы (текстовые). Массивы
3D моделирование в программе Tinkercad
Load testing with Visual Studio Enterprise 2015
Информация, ее свойства. Информация и управление
Информационные технологии в ДОУ
Security. The goal
Интернет желісіне жалпы сипаттама
Особенности работы с информацией в различных типах источников. Лекция 3
Презентация к уроку информатики в 5 классе по теме Метод координат
Обратная связь
Email:
Нажмите что бы посмотреть
window.__NUXT__=(function(a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S){return {data:{meta:{result:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F}},item:{result:{id:139284,name:k,category:G,count:42,jpg:"jpg\u002F139284",hits:H,download:b,h1:"Generics. (Lecture 7.3) презентация",meta:{h1:k,title:k,description:"Generics. (Lecture 7.3) презентация на тему, доклад, Информатика",keywords:"Generics. (Lecture 7.3), презентация, доклад, проект, скачать, на тему, PowerPoint, урок, класс, школа, Информатика",download_link:a},text:"Вы можете изучить и скачать доклад-презентацию на тему Презентация на тему Generics. (Lecture 7.3) из раздела Информатика. Презентация на заданную тему содержит 42 слайдов. Для просмотра воспользуйтесь проигрывателем, если материал оказался полезным для Вас - поделитесь им с друзьями с помощью социальных кнопок и добавьте наш сайт презентаций в закладки!",seo_text:"\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E \u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E",file:"Generics.-(Lecture-7.3).pptx",texts:["\u003Cp\u003EGenerics\u003Cbr\u003E","\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E","\u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E","\u003Cp\u003EA class that holds a single object\u003Cbr\u003Eclass Automobile {}\u003Cbr\u003Epublic class Holder1 {\u003Cbr\u003E private Automobile a;\u003Cbr\u003E public Holder1(Automobile a) {\u003Cbr\u003E this.a = a;\u003Cbr\u003E }\u003Cbr\u003E Automobile get() { return a; }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EA class that holds an Object\u003Cbr\u003Epublic class Holder2 { \r\n private Object a; \r\n public Holder2(Object a) { this.a = a; } \r\n\r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder2 h2 = new Holder2(new Automobile()); \r\n Automobile a = (Automobile) h2.get(); \r\n h2.set(\"Not an Automobile\"); \r\n String s = (String) h2.get(); \r\n h2.set(1); \u002F\u002F Autoboxes to Integer \r\n Integer x = (Integer) h2.get(); \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003ESimple generic class\u003Cbr\u003E\r\npublic class Holder3\u003CT\u003E { \u003Cbr\u003E private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder3\u003CAutomobile\u003E h3 =\r\n new Holder3\u003CAutomobile\u003E(new Automobile()); \r\n Automobile a = h3.get(); \u002F\u002F No cast needed \r\n \u002F\u002F h3.set(\"Not an Automobile\"); \u002F\u002F Error \r\n \u002F\u002F h3.set(1); \u002F\u002F Error \r\n } \r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Types and Methods\u003Cbr\u003E\u003Cp\u003EThere can be:\u003Cbr\u003EGeneric classes\u003Cbr\u003EGeneric interfaces\u003Cbr\u003EGeneric methods\u003Cbr\u003EBounded generic types\u003Cbr\u003EGeneric wildcards\u003Cbr\u003E","\u003Cp\u003EThe core idea of Java generics: You tell it what type you want to use, and it takes care of the details.\u003Cbr\u003E","\u003Cp\u003EType erasure\u003Cbr\u003E\u003Cp\u003EJava generics are implemented using type erasure. This means that any specific type information is erased when you compile your code.\u003Cbr\u003E","\u003Cp\u003EHow type erasure works?\u003Cbr\u003E\u003Cp\u003Epublic class Holder3\u003CT\u003E { \r\n private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3\u003CLong\u003E h3 =\u003Cbr\u003E new Holder3\u003CLong\u003E(1L);\u003Cbr\u003ELong n = h3.get();\u003Cbr\u003E\u003Cp\u003Epublic class Holder3 { \r\n private Object a; \r\n\r\n public Holder3(Object a) { this.a = a; } \r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3 h3 = new Holder3(1L);\u003Cbr\u003ELong n = (Long) h3.get();\u003Cbr\u003E","\u003Cp\u003ECompensating for erasure\r\n\r\npublic class Erased\u003CT\u003E {\r\n private final int SIZE = 100;\r\n\r\n public static void f(Object arg) {\r\n if(arg instanceof T) {} \u002F\u002F Error\r\n T var = new T(); \u002F\u002F Error\r\n T[] array = new T[SIZE]; \u002F\u002F Error\r\n T[] array = (T[])new Object[SIZE]; \u002F\u002F Unchecked \t\t\t\t\t\t\twarning\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric class with two types\r\n\r\npublic class TwoTuple\u003CA, B\u003E { \r\n public final A first; \r\n public final B second; \r\n\r\n public TwoTuple(A a, B b) { first = a; second = b; } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \")\"; \r\n } \r\n} \u003Cbr\u003E","\u003Cp\u003EYou cannot use primitives as type parameters!\r\n\r\nTwoTuple\u003CString, Integer\u003E ttsi = new TwoTuple\u003CString, Integer\u003E(\"hi\", 47);\r\n\r\nbut not\r\n\r\nTwoTuple\u003Cdouble, int\u003E ttdi = new TwoTuple\u003Cdouble, int\u003E(47.0, 47);\u003Cbr\u003E","\u003Cp\u003EInheritance with generic classes\r\n\r\npublic class ThreeTuple\u003CA, B, C\u003E extends TwoTuple\u003CA, B\u003E { \r\n public final C third; \r\n\r\n public ThreeTuple(A a, B b, C c) { \r\n super(a, b); \r\n third = c; \r\n } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \", \" +\r\n third +\")\"; \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric interface\u003Cbr\u003E\r\npublic interface Generator\u003CT\u003E { T next(); }\r\n\r\npublic class Fibonacci implements Generator\u003CInteger\u003E {\r\n private int count = 0;\r\n public Integer next() { return fib(count++); }\u003Cbr\u003E \u003Cbr\u003E ...\u003Cbr\u003E\r\n public static void main(String[] args) {\r\n Fibonacci gen = new Fibonacci();\r\n for(int i = 0; i \u003C 18; i++)\r\n System.out.print(gen.next() + \" \");\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Methods\r\n\r\npublic class GenericMethods {\r\n public \u003CT\u003E void f(T x) {\r\n System.out.println(x.getClass().getName());\r\n }\r\n public static void main(String[] args) {\r\n GenericMethods gm = new GenericMethods();\r\n gm.f(\"\");\r\n gm.f(1);\r\n gm.f(1.0);\r\n gm.f('c');\r\n gm.f(new String[] {“H”, “W”});\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EThe Syntax for Invoking a Generic Method\u003Cbr\u003EGenerics have an optional syntax for specifying the type for a generic method. You can place the data type of the generic in angle brackets, \u003C \u003E , after the dot operator and before the method call.\u003Cbr\u003E\r\n gm.\u003CString\u003Ef(“a string object”);\r\n gm.\u003CInteger\u003Ef(1);\r\n gm.\u003CDouble\u003Ef(1.0);\r\n gm.\u003CChar\u003Ef('c');\u003Cbr\u003E gm.\u003CString[]\u003Ef(new String[] {“H”, “W”});\u003Cbr\u003EThe syntax makes the code more readable and also gives you control over the generic type in situations where the type might not be obvious.\u003Cbr\u003E","\u003Cp\u003ELeveraging type argument inference \r\n\r\npublic class Tuple {\r\n public static \u003CA,B\u003E TwoTuple\u003CA,B\u003E tuple(A a, B b) {\r\n return new TwoTuple\u003CA,B\u003E(a, b);\r\n }\r\n public static \u003CA,B,C\u003E ThreeTuple\u003CA,B,C\u003E tuple(A a,B b,C c) {\r\n return new ThreeTuple\u003CA,B,C\u003E(a, b, c);\r\n }\r\n}\r\n...\r\nTwoTuple\u003CString, Integer\u003E ttsi = Tuple.tuple(“hi”, 47);\r\nThreeTuple\u003CString,Integer,Double\u003E ttsid=Tuple.tuple(“hi”,47,47.0);\u003Cbr\u003E","\u003Cp\u003EAnonymous inner classes\r\n\r\npublic interface Generator\u003CT\u003E { T next(); } \r\n\r\nclass Customer { \r\n private Customer() {} \r\n\r\n public static Generator\u003CCustomer\u003E generator() { \r\n return new Generator\u003CCustomer\u003E() { \r\n public Customer next() { return new Customer(); } \r\n }; \r\n } \r\n} \r\n...\r\nCustomer customer1 = Customer.generator().next();\r\nCustomer customer2 = Customer.generator().next();\u003Cbr\u003E","\u003Cp\u003EBounded Generic Types\u003Cbr\u003EBecause erasure removes type information, the only methods you can call for an unbounded generic parameter are those available for Object. Bounds allow you to place constraints on the parameter types. Important effect is that you can call methods that are in your bound types.\u003Cbr\u003Einterface HasColor {\u003Cbr\u003E Color getColor();\u003Cbr\u003E}\u003Cbr\u003Eclass Colored\u003CT extends HasColor\u003E {\r\n T item;\u003Cbr\u003E public Colored(T item) { this.item = item; }\u003Cbr\u003E public T getItem() { return item; }\r\n\u003Cbr\u003E \u002F\u002F The bound allows you to call a method:\r\n public Color color() { return item.getColor(); }\r\n}\u003Cbr\u003E","\u003Cp\u003ECompound bounds\u003Cbr\u003Eclass Dimension { public int x, y, z; } \u003Cbr\u003E\u002F\u002F Multiple bounds: \r\nclass ColoredDimension\u003CT extends Dimension & HasColor\u003E { \r\n T item; \r\n ColoredDimension(T item) { this.item = item; } \r\n T getItem() { return item; } \r\n Color color() { return item.getColor(); } \r\n int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EBounds and Inheritance\u003Cbr\u003E\r\nclass HoldItem\u003CT\u003E {\r\n T item;\r\n HoldItem(T item) { this.item = item; }\r\n T getItem() { return item; }\r\n}\u003Cbr\u003E\r\nclass Colored2\u003CT extends HasColor\u003E extends HoldItem\u003CT\u003E { \r\n \u002F\u002F some code here...\u003Cbr\u003E Color color() { return item.getColor(); } \r\n}\u003Cbr\u003E\r\nclass ColoredDimension2\u003CT extends Dimension & HasColor\u003E\r\n extends Colored2\u003CT\u003E {\r\n \u002F\u002F some code here...\u003Cbr\u003E int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EPolymorphism and Generics\u003Cbr\u003E\r\nclass Holder\u003CT\u003E {\r\n T item;\r\n void set(T item) { this.item = item; }\r\n T get() { return item; }\r\n}\r\nabstract class Parent { }\u003Cbr\u003Eclass Child extends Parent { }\u003Cbr\u003Eclass AnotherChild extends Parent { }\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CChild\u003E h1 = new Holder\u003CChild\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h2 = new Holder\u003CParent\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h3 = new Holder\u003CChild\u003E(); \u002F\u002F Error\u003Cbr\u003E\u002F\u002F because one could do this:\u003Cbr\u003E\u002F\u002F h3.set(new AnotherChild());\u003Cbr\u003E","\u003Cp\u003EWhy Polymorphism doesn’t work\u003Cbr\u003E\u003Cp\u003Eclass Holder\u003CT\u003E {\r\n T[] items;\u003Cbr\u003E int num = 0;\r\n void add(T item) { this.items[num++] = item;}\r\n T[] get() { return items; }\r\n}\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CInteger\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003EHolder\u003CNumber\u003E reg = h;\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003EInteger i3 = h.get()[2]\u003Cbr\u003ESo Double is a Number but Holder\u003CDouble\u003E is not Holder\u003CNumber\u003E \u003Cbr\u003E\u003Cp\u003EClass case exception Double != Integer\u003Cbr\u003E\u003Cp\u003Eh -\u003E {Integer, Integer, Double}\u003Cbr\u003E\u003Cp\u003EIf polymorphism was allowed this would be legal\u003Cbr\u003E\u003Cp\u003EThis is also legal since Double is a Number\u003Cbr\u003E","\u003Cp\u003EBut you can do this:\u003Cbr\u003E\u003Cp\u003EThis is how you can put different object types in parameterized Holder object:\u003Cbr\u003EHolder\u003CNumber\u003E h = new Holder\u003CNumber\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003ENumber i3 = h.get()[2]\u003Cbr\u003E\u003Cp\u003EBoth Integer and Double are the Numbers\u003Cbr\u003E","\u003Cp\u003EMore Example\u003Cbr\u003Eabstract class Animal { public abstract void check(); }\u003Cbr\u003Eclass Dog extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Dog\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass Cat extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Cat\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003CAnimal\u003E animal) {\u003Cbr\u003E animal.get().check();\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F Error\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F Error\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EGeneric Wildcards (?)\u003Cbr\u003E\u003Cp\u003EThe wildcard provides a polymorphic - like behavior for declaring generics.\u003Cbr\u003E\u003C?\u003E , an unbounded wildcard\u003Cbr\u003E\u003C? extends type\u003E , a wildcard with an upper bound\u003Cbr\u003E\u003C? super type\u003E , a wildcard with a lower bound\u003Cbr\u003E","\u003Cp\u003EUnbounded Wildcards\u003Cbr\u003E\u003Cp\u003EThe unbounded wildcard represents any data type, similar to the \u003C T \u003E syntax. \u003Cbr\u003Epublic static void printList(List\u003C?\u003E list) {\u003Cbr\u003E for(Object x : list) {\u003Cbr\u003E System.out.println(x.toString());\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E...\u003Cbr\u003EArrayList\u003CString\u003E keywords = new ArrayList\u003CString\u003E();\u003Cbr\u003Ekyewords.add(“generic”);\u003Cbr\u003EprintList(keywords);\u003Cbr\u003EUse the ? in situations where you do not need a formal parameter type like \u003C T \u003E\u003Cbr\u003E\u003Cp\u003EData type is not required here\u003Cbr\u003E","\u003Cp\u003EBe careful\u003Cbr\u003E\u003Cp\u003EHolder\u003C?\u003E h = new Holder\u003CString\u003E();\u003Cbr\u003Eh.add(new Object()); \u002F\u002F compile time error\u003Cbr\u003Eh.add(new String()); \u002F\u002F compile time error\u003Cbr\u003E\u002F\u002F one exception!\u003Cbr\u003Eh.add(null); \u002F\u002F null is member of every type\u003Cbr\u003E\u003Cbr\u003EWorking with unbounded wildcards we can only read data, not assign!\u003Cbr\u003E\u003Cbr\u003E","\u003Cp\u003EUpper - Bound Wildcards\u003Cbr\u003E\u003Cp\u003EBounded wildcards put some restrictions on unknown type:\u003Cbr\u003Epublic static void printList(List\u003C? extends Number\u003E list){\u003Cbr\u003E for(Number x : list) {\u003Cbr\u003E System.out.println(x.doubleValue());\u003Cbr\u003E }\u003Cbr\u003E list.add(new Integer(3)); \u002F\u002F compile error\u003Cbr\u003E}\u003Cbr\u003E\u003Cp\u003ENow we know that object is instance of Number\u003Cbr\u003E\u003Cp\u003EBut we still don’t know exact type, so can’t modify list\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? extends Animal\u003E animal) {\u003Cbr\u003E animal.get().check(); \u002F\u002F OK\u003Cbr\u003E animal.set(new Cat()); \u002F\u002F Error: we don’t know exact parameter type of animal\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003ELower Bounded Wildcards\u003Cbr\u003E\u003Cp\u003Ea lower bounded wildcard restricts the unknown type to be a specific type or a super type of that type\u003Cbr\u003EHolder\u003C? super Integer\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(new Integer(1));\u003Cbr\u003EInteger i1 = h.get(); \u002F\u002F compilation error\u003Cbr\u003E\t\t\t\u002F\u002F get returns Object\u003Cbr\u003EInteger i2 = (Integer)h.get(); \u002F\u002F OK\u003Cbr\u003ELower bounded wildcards allow to modify but not read!!\u003Cbr\u003E","\u003Cp\u003EExample\u003Cbr\u003E\u003Cp\u003Epublic static void addNumbers(List\u003C? super Integer\u003E list) {\u003Cbr\u003E for (int i = 1; i \u003C= 10; i++) {\u003Cbr\u003E list.add(i);\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003EList\u003CInteger\u003E i = new ArrayList\u003CInteger\u003E();\u003Cbr\u003EList\u003CNumber\u003E n = new ArrayList\u003CNumber\u003E();\u003Cbr\u003EList\u003CObject\u003E o = new ArrayList\u003CObject\u003E();\u003Cbr\u003E\t\t\u003Cbr\u003EaddNumbers(i);\u003Cbr\u003EaddNumbers(n);\u003Cbr\u003EaddNumbers(o);\u003Cbr\u003EThis works fine\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? super Dog\u003E dog) {\u003Cbr\u003E animal.get().check(); \u002F\u002F Error!\u003Cbr\u003E \u002F\u002F get() returns Object ref\u003Cbr\u003E animal.set(new Dog()); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CAnimal\u003E animal = new Holder\u003CAnimal\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat= new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(animal); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002FError: Cat isn’t super of Dog\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EWhat's the difference?\u003Cbr\u003Evoid check(Holder\u003C?\u003E holder) { }\u003Cbr\u003Evoid check(Holder\u003CObject\u003E holder) { }\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003CObject\u003E obj) {\u003Cbr\u003E obj.set(new Dog());\u003Cbr\u003E obj.set(new Cat());\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CObject\u003E obj = new Holder\u003CObject\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(obj); \u002F\u002F Only Holder\u003CObject\u003E goes here!\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003C?\u003E obj) {\u003Cbr\u003E obj.set(new Dog()); \u002F\u002F Error\u003Cbr\u003E \u002F\u002F Compiler isn't sure that it's really Dog Holder\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CInteger\u003E integer = new Holder\u003CInteger\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(dog); \u002F\u002F OK\u003Cbr\u003E main.check(integer); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E",I,I,"\u003Cp\u003ENaming Conventions for Generics\u003Cbr\u003E\u003Cp\u003EE for an element\u003Cbr\u003EK for a map key\u003Cbr\u003EV for a map value\u003Cbr\u003EN for a number\u003Cbr\u003ET for a generic data type\u003Cbr\u003EUse S , U , V , and so on for multiple types in the same class.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E1) Generics let you enforce compile-time type safety.\u003Cbr\u003EHolder\u003CString\u003E h1 = new Holder\u003CString\u003E();\u003Cbr\u003EHolder h2 = new Holder();\u003Cbr\u003EString s = h1.get(); \u002F\u002F no cast needed\u003Cbr\u003EString s = (String) h2.get(); \u002F\u002F cast required\u003Cbr\u003E2) Generic type information does not exist at runtime — it is for compile-time safety only.\u003Cbr\u003E3) Polymorphic assignment don't apply to the generic type\u003Cbr\u003EHolder\u003CAnimal\u003E h1 = new Holder\u003CDog\u003E(); \u002F\u002F Error\u003Cbr\u003E4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:\u003Cbr\u003Evoid foo(List\u003CDog\u003E d) {} \u002F\u002F can take only \u003CDog\u003E\u003Cbr\u003Evoid foo(List\u003C? extends Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CCollie\u003E\u003Cbr\u003Evoid foo(List\u003C? super Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CAnimal\u003E\u003Cbr\u003E5) When using a wildcard, List\u003C? extends Dog\u003E, the collection can be accessed but not modified.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E6) The generics type identifier can be used in class, method, and variable declarations:\u003Cbr\u003E class Foo\u003Ct\u003E { } \u002F\u002F a class\u003Cbr\u003E T anInstance; \u002F\u002F an instance variable\u003Cbr\u003E Foo(T aRef) {} \u002F\u002F a constructor argument\u003Cbr\u003E void bar(T aRef) {} \u002F\u002F a method argument\u003Cbr\u003E T baz() {} \u002F\u002F a return type\u003Cbr\u003E7) You can use more than one parameterized type in a declaration:\u003Cbr\u003E public class UseTwo\u003CT, X\u003E { }\u003Cbr\u003E8) You can declare a generic method using a type not defined in the class:\u003Cbr\u003E public \u003CT\u003E T returnMe(T t) { return t; }\u003Cbr\u003EReading in Russian\u003Cbr\u003Ehttp:\u002F\u002Fwww.rsdn.ru\u002Farticle\u002Fjava\u002Fgenericsinjava.xml\u003Cbr\u003E"],href:"\u002Finformatika\u002Fgenerics-lecture-73",href_category:"\u002Finformatika",date:1628090801,related:[{id:404222,name:"Научно-техническая информация",href:"\u002Finformatika\u002Fnauchno-tehnicheskaya-informatsiya-1",jpg:"jpg\u002F404222"},{id:478755,name:"Презентация к аттестации учителя информатики",href:"\u002Finformatika\u002Fprezentatsiya-k-attestatsii-uchitelya-informatiki",jpg:"jpg\u002F478755"},{id:4499,name:"Основные компоненты ПК",href:"\u002Finformatika\u002Fosnovnye-komponenty-pk",jpg:"jpg\u002F4499"},{id:184558,name:"Арифметические основы организации ЭВМ",href:"\u002Finformatika\u002Farifmeticheskie-osnovy-organizatsii-evm",jpg:"jpg\u002F184558"},{id:373746,name:"Вёрстка и дизайн газетной статьи",href:"\u002Finformatika\u002Fvyorstka-i-dizayn-gazetnoy-stati",jpg:"jpg\u002F373746"},{id:577279,name:"Алгоритм действий родителей для прохождения регистрации их детей младше\u002Fстарше 14 лет во ФГИС Моя школа",href:"\u002Finformatika\u002Falgoritm-deystviy-roditeley-dlya-prohozhdeniya-registratsii",jpg:"jpg\u002F577279"},{id:12068,name:"Керування правами доступу",href:"\u002Finformatika\u002Fkeruvannya-pravami-dostupu",jpg:"jpg\u002F12068"},{id:403270,name:"Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)",href:"\u002Finformatika\u002Fponyatie-algoritma-svoystva-vidy-tipy-formy",jpg:"jpg\u002F403270"},{id:234266,name:"Взаимодействие клиента и сервера",href:"\u002Finformatika\u002Fvzaimodeystvie-klienta-i-servera",jpg:"jpg\u002F234266"},{id:266792,name:"Как с нуля запустить Онлайн-школу",href:"\u002Finformatika\u002Fkak-s-nulya-zapustit-onlayn-shkolu",jpg:"jpg\u002F266792"},{id:104353,name:"Программа Project Expert",href:"\u002Finformatika\u002Fprogramma-project-expert",jpg:"jpg\u002F104353"},{id:3725,name:"What is cryptocurrency",href:"\u002Finformatika\u002Fwhat-is-cryptocurrency",jpg:"jpg\u002F3725"},{id:1966,name:"История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД",href:"\u002Finformatika\u002Fistoriya-razvitiya-i-pokoleniya-subd-klassifikatsiya",jpg:"jpg\u002F1966"},{id:253599,name:"WORD-тын графикалык мумкіндіктері",href:"\u002Finformatika\u002Fword-tyn-grafikalyk-mumkndkter",jpg:"jpg\u002F253599"},{id:215026,name:"Компьютер как универсальное устройство обработки информации",href:"\u002Finformatika\u002Fkompyuter-kak-universalnoe-ustroystvo-obrabotki-informatsii",jpg:"jpg\u002F215026"},{id:200593,name:"Линейное программирование",href:"\u002Finformatika\u002Flineynoe-programmirovanie-2",jpg:"jpg\u002F200593"},{id:429765,name:"ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области",href:"\u002Finformatika\u002Fou-novoseletskaya-shkola-navigator-dopolnitelnogo-obrazovaniya",jpg:"jpg\u002F429765"},{id:383037,name:"Социальная память. Функция социальной памяти",href:"\u002Finformatika\u002Fsotsialnaya-pamyat-funktsiya-sotsialnoy-pamyati",jpg:"jpg\u002F383037"},{id:160929,name:"Різновиди діаграм та їх форматування",href:"\u002Finformatika\u002Frznovidi-dagram-ta-h-formatuvannya",jpg:"jpg\u002F160929"},{id:266355,name:"Лекция 2. Файлы (текстовые). Массивы",href:"\u002Finformatika\u002Flektsiya-2-fayly-tekstovye-massivy",jpg:"jpg\u002F266355"},{id:610347,name:"3D моделирование в программе Tinkercad",href:"\u002Finformatika\u002F3d-modelirovanie-v-programme-tinkercad",jpg:"jpg\u002F610347"},{id:393791,name:"Load testing with Visual Studio Enterprise 2015",href:"\u002Finformatika\u002Fload-testing-with-visual-studio-enterprise",jpg:"jpg\u002F393791"},{id:114799,name:"Информация, ее свойства. Информация и управление",href:"\u002Finformatika\u002Finformatsiya-ee-svoystva-informatsiya-i-upravlenie",jpg:"jpg\u002F114799"},{id:435506,name:"Информационные технологии в ДОУ",href:"\u002Finformatika\u002Finformatsionnye-tehnologii-v-dou",jpg:"jpg\u002F435506"},{id:439332,name:"Security. The goal",href:"\u002Finformatika\u002Fsecurity-the-goal",jpg:"jpg\u002F439332"},{id:15166,name:"Интернет желісіне жалпы сипаттама",href:"\u002Finformatika\u002Finternet-zhelsne-zhalpy-sipattama",jpg:"jpg\u002F15166"},{id:326320,name:"Особенности работы с информацией в различных типах источников. Лекция 3",href:"\u002Finformatika\u002Fosobennosti-raboty-s-informatsiey-v-razlichnyh",jpg:"jpg\u002F326320"},{id:503963,name:"Презентация к уроку информатики в 5 классе по теме Метод координат",href:"\u002Finformatika\u002Fprezentatsiya-k-uroku-informatiki-v-5-6",jpg:"jpg\u002F503963"}],navigation:{next:"\u002Fliteratura\u002Ftragediya-gyote-faust-2",next_name:"Трагедия Гёте Фауст",prev:"\u002Finformatika\u002Finternet-technologies-2",prev_name:"Internet technologies"}}},categories:{result:[{id:J,ordering:b,name:"Без категории",pseudoname:"uncategorized"},{id:H,ordering:b,name:"Бизнес",pseudoname:"biznes"},{id:146,ordering:b,name:"Образование",pseudoname:"obrazovanie"},{id:149,ordering:b,name:"Финансы",pseudoname:"finansy"},{id:150,ordering:b,name:"Государство",pseudoname:"gosudarstvo"},{id:152,ordering:b,name:"Спорт",pseudoname:"sport"},{id:154,ordering:b,name:"Армия",pseudoname:"armiya"},{id:156,ordering:b,name:"Культурология",pseudoname:"kulturologiya"},{id:157,ordering:b,name:"Еда и кулинария",pseudoname:"eda-i-kulinariya"},{id:158,ordering:b,name:"Лингвистика",pseudoname:"lingvistika"},{id:163,ordering:b,name:"Черчение",pseudoname:"cherchenie"},{id:164,ordering:b,name:"Физкультура",pseudoname:"fizkultura"},{id:165,ordering:b,name:"ИЗО",pseudoname:"izo"},{id:166,ordering:b,name:"Психология",pseudoname:"psihologiya"},{id:116,ordering:J,name:"Английский язык",pseudoname:"angliyskiy-yazyk"},{id:108,ordering:2,name:"Астрономия",pseudoname:"astronomiya"},{id:104,ordering:3,name:"Алгебра",pseudoname:"algebra"},{id:106,ordering:4,name:"Биология",pseudoname:"biologiya"},{id:142,ordering:5,name:"География",pseudoname:"geografiya"},{id:141,ordering:6,name:"Геометрия",pseudoname:"geometria"},{id:123,ordering:7,name:"Детские презентации",pseudoname:"detskie-prezentatsii"},{id:107,ordering:8,name:G,pseudoname:"informatika"},{id:109,ordering:9,name:"История",pseudoname:"istoriya"},{id:139,ordering:10,name:"Литература",pseudoname:"literatura"},{id:119,ordering:11,name:"Маркетинг",pseudoname:"marketing"},{id:114,ordering:12,name:"Математика",pseudoname:"matematika"},{id:138,ordering:h,name:"Медицина",pseudoname:"medetsina"},{id:118,ordering:14,name:"Менеджмент",pseudoname:"menedzhment"},{id:137,ordering:15,name:"Музыка",pseudoname:"muzyka"},{id:136,ordering:16,name:"МХК",pseudoname:"mhk"},{id:130,ordering:17,name:"Немецкий язык",pseudoname:"nemetskiy-yazyk"},{id:105,ordering:18,name:"ОБЖ",pseudoname:"obzh"},{id:133,ordering:19,name:"Обществознание ",pseudoname:"obshchestvoznanie"},{id:132,ordering:20,name:"Окружающий мир ",pseudoname:"okruzhayushchiy-mir"},{id:131,ordering:21,name:"Педагогика ",pseudoname:"pedagogika"},{id:129,ordering:22,name:"Русский язык",pseudoname:"russkiy-yazyk"},{id:128,ordering:24,name:"Технология",pseudoname:"tehnologiya"},{id:127,ordering:25,name:"Физика",pseudoname:"fizika"},{id:126,ordering:26,name:"Философия",pseudoname:"filosofiya"},{id:125,ordering:27,name:"Химия",pseudoname:"himiya"},{id:124,ordering:29,name:"Экология",pseudoname:"ekologiya"},{id:121,ordering:30,name:"Экономика",pseudoname:"ekonomika"},{id:120,ordering:31,name:"Юриспруденция",pseudoname:"yurisprudentsiya"}]}},state:{},_errors:{},serverRendered:e,config:{public:{SITE_NAME:K,SITE_HOST:"mypreza.com",SITE_LANG:L,API_BASE_URL:"https:\u002F\u002Fmypreza.com\u002Fapi\u002F",pwaManifest:{name:K,short_name:a,description:a,lang:L,start_url:"\u002F?standalone=true",display:"standalone",background_color:j,theme_color:"#000000",icons:[{src:"\u002F_nuxt\u002Ficons\u002F64x64.f2a6e93d.png",type:d,sizes:M,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F64x64.maskable.f2a6e93d.png",type:d,sizes:M,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F120x120.f2a6e93d.png",type:d,sizes:N,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F120x120.maskable.f2a6e93d.png",type:d,sizes:N,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F144x144.f2a6e93d.png",type:d,sizes:O,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F144x144.maskable.f2a6e93d.png",type:d,sizes:O,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F152x152.f2a6e93d.png",type:d,sizes:P,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F152x152.maskable.f2a6e93d.png",type:d,sizes:P,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F192x192.f2a6e93d.png",type:d,sizes:Q,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F192x192.maskable.f2a6e93d.png",type:d,sizes:Q,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F384x384.f2a6e93d.png",type:d,sizes:R,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F384x384.maskable.f2a6e93d.png",type:d,sizes:R,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F512x512.f2a6e93d.png",type:d,sizes:S,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F512x512.maskable.f2a6e93d.png",type:d,sizes:S,purpose:g}]},yandexMetrika:{id:"85004146",metrikaUrl:"https:\u002F\u002Fmc.yandex.ru\u002Fmetrika\u002Ftag.js",accurateTrackBounce:e,childIframe:c,clickmap:c,defer:c,useRuntimeConfig:e,trackHash:c,trackLinks:e,type:b,webvisor:c,triggerEvent:c,consoleLog:e,partytown:c,isDev:c}},app:{baseURL:"\u002F",buildAssetsDir:"\u002F_nuxt\u002F",cdnURL:a}},pinia:{app:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F,token:a}}}}("",0,false,"image\u002Fpng",true,"any","maskable",13,"#d53032","#ffffff","Generics. (Lecture 7.3)","Учебные презентации","Презентации в PowerPoint на разные темы","Презентации, проекты, доклады в PowerPoint на разные темы для учебы","Презентация, на тему, урок, класс, PowerPoint, скачати презентацію, фон, шаблон, доклад, проект.","images\u002Fdata\u002Flogo.png",185,40,720,480,"6LeioWIpAAAAAGqMN4KqMVIkekcMW7fBKHjXCd-a","2503267","[e-mail]","h3a","text","none","h3","category","both",80,800,"\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fes5-shims\u002F0.0.2\u002Fes5-shims.min.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fshare2\u002Fshare.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cdiv class=\"ya-share2\" data-services=\"collections,gplus,vkontakte,facebook,odnoklassniki,gplus,twitter,moimir\" data-counter=\"\"\u003E\u003C\u002Fdiv\u003E","Информатика",144,"\u003Cp\u003EWhich will compile?\u003Cbr\u003E1) List\u003C?\u003E list = new ArrayList\u003CDog\u003E();\u003Cbr\u003E2) List\u003C? extends Animal\u003E aList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E3) List\u003C?\u003E foo = new ArrayList\u003C? extends Animal\u003E();\u003Cbr\u003E4) List\u003C? extends Dog\u003E cList = new ArrayList\u003CInteger\u003E();\u003Cbr\u003E5) List\u003C? super Dog\u003E bList = new ArrayList\u003CAnimal\u003E();\u003Cbr\u003E6) List\u003C? super Animal\u003E dList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E",1,"Mypreza","ru","64x64","120x120","144x144","152x152","192x192","384x384","512x512"))

More example
class AnimalDoctor {
void checkAnimal(Holder
dog) {
animal.get().check(); // Error! // get() returns Object ref
animal.set(new Dog()); // OK
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
animal = new Holder
();
Holder
cat= new Holder
();
AnimalDoctor doctor = new AnimalDoctor();
doctor.checkAnimal(dog); // OK
doctor.checkAnimal(animal); // OK
doctor.checkAnimal(cat); //Error: Cat isn’t super of Dog
}
}

What's the difference?
void check(Holder
holder) { }
void check(Holder
holder) { }
Слайд 36
There IS a huge difference!
class Main {
void check(Holder
obj) {
obj.set(new Dog());
obj.set(new Cat());
}
public static void main(String[] args) {
Holder
obj = new Holder
();
Main main = new Main();
main.check(obj); // Only Holder
goes here!
}
}
Слайд 37
There IS a huge difference!
class Main {
void check(Holder
obj) {
obj.set(new Dog());
// Error
// Compiler isn't sure that it's really Dog Holder
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
integer = new Holder
();
Main main = new Main();
main.check(dog); // OK
main.check(integer); // OK
}
}
Слайд 38
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 39
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 40
Naming Conventions for Generics
E for an element
K for a map key
V for a
map value
N for a number
T for a generic data type
Use S , U , V , and so on for multiple types in the same class.
Слайд 41
Summary
1) Generics let you enforce compile-time type safety.
Holder
h1 = new Holder
();
Holder h2 =
new Holder();
String s = h1.get(); // no cast needed
String s = (String) h2.get(); // cast required
2) Generic type information does not exist at runtime — it is for compile-time safety only.
3) Polymorphic assignment don't apply to the generic type
Holder
h1 = new Holder
(); // Error
4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:
void foo(List
d) {} // can take only
void foo(List
) {} // take a
or
void foo(List
) {} // take a
or
5) When using a wildcard, List
, the collection can be accessed but not modified.
Имя файла: Generics.-(Lecture-7.3).pptx
Количество просмотров: 144
Количество скачиваний: 0
Скачать
- Предыдущая
Internet technologies
Следующая -
Трагедия Гёте Фауст
Похожие презентации
Научно-техническая информация
Презентация к аттестации учителя информатики
Основные компоненты ПК
Арифметические основы организации ЭВМ
Вёрстка и дизайн газетной статьи
Алгоритм действий родителей для прохождения регистрации их детей младше/старше 14 лет во ФГИС Моя школа
Керування правами доступу
Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)
Взаимодействие клиента и сервера
Как с нуля запустить Онлайн-школу
Программа Project Expert
What is cryptocurrency
История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД
WORD-тын графикалык мумкіндіктері
Компьютер как универсальное устройство обработки информации
Линейное программирование
ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области
Социальная память. Функция социальной памяти
Різновиди діаграм та їх форматування
Лекция 2. Файлы (текстовые). Массивы
3D моделирование в программе Tinkercad
Load testing with Visual Studio Enterprise 2015
Информация, ее свойства. Информация и управление
Информационные технологии в ДОУ
Security. The goal
Интернет желісіне жалпы сипаттама
Особенности работы с информацией в различных типах источников. Лекция 3
Презентация к уроку информатики в 5 классе по теме Метод координат
Обратная связь
Email:
Нажмите что бы посмотреть
window.__NUXT__=(function(a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S){return {data:{meta:{result:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F}},item:{result:{id:139284,name:k,category:G,count:42,jpg:"jpg\u002F139284",hits:H,download:b,h1:"Generics. (Lecture 7.3) презентация",meta:{h1:k,title:k,description:"Generics. (Lecture 7.3) презентация на тему, доклад, Информатика",keywords:"Generics. (Lecture 7.3), презентация, доклад, проект, скачать, на тему, PowerPoint, урок, класс, школа, Информатика",download_link:a},text:"Вы можете изучить и скачать доклад-презентацию на тему Презентация на тему Generics. (Lecture 7.3) из раздела Информатика. Презентация на заданную тему содержит 42 слайдов. Для просмотра воспользуйтесь проигрывателем, если материал оказался полезным для Вас - поделитесь им с друзьями с помощью социальных кнопок и добавьте наш сайт презентаций в закладки!",seo_text:"\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E \u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E",file:"Generics.-(Lecture-7.3).pptx",texts:["\u003Cp\u003EGenerics\u003Cbr\u003E","\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E","\u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E","\u003Cp\u003EA class that holds a single object\u003Cbr\u003Eclass Automobile {}\u003Cbr\u003Epublic class Holder1 {\u003Cbr\u003E private Automobile a;\u003Cbr\u003E public Holder1(Automobile a) {\u003Cbr\u003E this.a = a;\u003Cbr\u003E }\u003Cbr\u003E Automobile get() { return a; }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EA class that holds an Object\u003Cbr\u003Epublic class Holder2 { \r\n private Object a; \r\n public Holder2(Object a) { this.a = a; } \r\n\r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder2 h2 = new Holder2(new Automobile()); \r\n Automobile a = (Automobile) h2.get(); \r\n h2.set(\"Not an Automobile\"); \r\n String s = (String) h2.get(); \r\n h2.set(1); \u002F\u002F Autoboxes to Integer \r\n Integer x = (Integer) h2.get(); \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003ESimple generic class\u003Cbr\u003E\r\npublic class Holder3\u003CT\u003E { \u003Cbr\u003E private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder3\u003CAutomobile\u003E h3 =\r\n new Holder3\u003CAutomobile\u003E(new Automobile()); \r\n Automobile a = h3.get(); \u002F\u002F No cast needed \r\n \u002F\u002F h3.set(\"Not an Automobile\"); \u002F\u002F Error \r\n \u002F\u002F h3.set(1); \u002F\u002F Error \r\n } \r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Types and Methods\u003Cbr\u003E\u003Cp\u003EThere can be:\u003Cbr\u003EGeneric classes\u003Cbr\u003EGeneric interfaces\u003Cbr\u003EGeneric methods\u003Cbr\u003EBounded generic types\u003Cbr\u003EGeneric wildcards\u003Cbr\u003E","\u003Cp\u003EThe core idea of Java generics: You tell it what type you want to use, and it takes care of the details.\u003Cbr\u003E","\u003Cp\u003EType erasure\u003Cbr\u003E\u003Cp\u003EJava generics are implemented using type erasure. This means that any specific type information is erased when you compile your code.\u003Cbr\u003E","\u003Cp\u003EHow type erasure works?\u003Cbr\u003E\u003Cp\u003Epublic class Holder3\u003CT\u003E { \r\n private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3\u003CLong\u003E h3 =\u003Cbr\u003E new Holder3\u003CLong\u003E(1L);\u003Cbr\u003ELong n = h3.get();\u003Cbr\u003E\u003Cp\u003Epublic class Holder3 { \r\n private Object a; \r\n\r\n public Holder3(Object a) { this.a = a; } \r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3 h3 = new Holder3(1L);\u003Cbr\u003ELong n = (Long) h3.get();\u003Cbr\u003E","\u003Cp\u003ECompensating for erasure\r\n\r\npublic class Erased\u003CT\u003E {\r\n private final int SIZE = 100;\r\n\r\n public static void f(Object arg) {\r\n if(arg instanceof T) {} \u002F\u002F Error\r\n T var = new T(); \u002F\u002F Error\r\n T[] array = new T[SIZE]; \u002F\u002F Error\r\n T[] array = (T[])new Object[SIZE]; \u002F\u002F Unchecked \t\t\t\t\t\t\twarning\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric class with two types\r\n\r\npublic class TwoTuple\u003CA, B\u003E { \r\n public final A first; \r\n public final B second; \r\n\r\n public TwoTuple(A a, B b) { first = a; second = b; } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \")\"; \r\n } \r\n} \u003Cbr\u003E","\u003Cp\u003EYou cannot use primitives as type parameters!\r\n\r\nTwoTuple\u003CString, Integer\u003E ttsi = new TwoTuple\u003CString, Integer\u003E(\"hi\", 47);\r\n\r\nbut not\r\n\r\nTwoTuple\u003Cdouble, int\u003E ttdi = new TwoTuple\u003Cdouble, int\u003E(47.0, 47);\u003Cbr\u003E","\u003Cp\u003EInheritance with generic classes\r\n\r\npublic class ThreeTuple\u003CA, B, C\u003E extends TwoTuple\u003CA, B\u003E { \r\n public final C third; \r\n\r\n public ThreeTuple(A a, B b, C c) { \r\n super(a, b); \r\n third = c; \r\n } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \", \" +\r\n third +\")\"; \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric interface\u003Cbr\u003E\r\npublic interface Generator\u003CT\u003E { T next(); }\r\n\r\npublic class Fibonacci implements Generator\u003CInteger\u003E {\r\n private int count = 0;\r\n public Integer next() { return fib(count++); }\u003Cbr\u003E \u003Cbr\u003E ...\u003Cbr\u003E\r\n public static void main(String[] args) {\r\n Fibonacci gen = new Fibonacci();\r\n for(int i = 0; i \u003C 18; i++)\r\n System.out.print(gen.next() + \" \");\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Methods\r\n\r\npublic class GenericMethods {\r\n public \u003CT\u003E void f(T x) {\r\n System.out.println(x.getClass().getName());\r\n }\r\n public static void main(String[] args) {\r\n GenericMethods gm = new GenericMethods();\r\n gm.f(\"\");\r\n gm.f(1);\r\n gm.f(1.0);\r\n gm.f('c');\r\n gm.f(new String[] {“H”, “W”});\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EThe Syntax for Invoking a Generic Method\u003Cbr\u003EGenerics have an optional syntax for specifying the type for a generic method. You can place the data type of the generic in angle brackets, \u003C \u003E , after the dot operator and before the method call.\u003Cbr\u003E\r\n gm.\u003CString\u003Ef(“a string object”);\r\n gm.\u003CInteger\u003Ef(1);\r\n gm.\u003CDouble\u003Ef(1.0);\r\n gm.\u003CChar\u003Ef('c');\u003Cbr\u003E gm.\u003CString[]\u003Ef(new String[] {“H”, “W”});\u003Cbr\u003EThe syntax makes the code more readable and also gives you control over the generic type in situations where the type might not be obvious.\u003Cbr\u003E","\u003Cp\u003ELeveraging type argument inference \r\n\r\npublic class Tuple {\r\n public static \u003CA,B\u003E TwoTuple\u003CA,B\u003E tuple(A a, B b) {\r\n return new TwoTuple\u003CA,B\u003E(a, b);\r\n }\r\n public static \u003CA,B,C\u003E ThreeTuple\u003CA,B,C\u003E tuple(A a,B b,C c) {\r\n return new ThreeTuple\u003CA,B,C\u003E(a, b, c);\r\n }\r\n}\r\n...\r\nTwoTuple\u003CString, Integer\u003E ttsi = Tuple.tuple(“hi”, 47);\r\nThreeTuple\u003CString,Integer,Double\u003E ttsid=Tuple.tuple(“hi”,47,47.0);\u003Cbr\u003E","\u003Cp\u003EAnonymous inner classes\r\n\r\npublic interface Generator\u003CT\u003E { T next(); } \r\n\r\nclass Customer { \r\n private Customer() {} \r\n\r\n public static Generator\u003CCustomer\u003E generator() { \r\n return new Generator\u003CCustomer\u003E() { \r\n public Customer next() { return new Customer(); } \r\n }; \r\n } \r\n} \r\n...\r\nCustomer customer1 = Customer.generator().next();\r\nCustomer customer2 = Customer.generator().next();\u003Cbr\u003E","\u003Cp\u003EBounded Generic Types\u003Cbr\u003EBecause erasure removes type information, the only methods you can call for an unbounded generic parameter are those available for Object. Bounds allow you to place constraints on the parameter types. Important effect is that you can call methods that are in your bound types.\u003Cbr\u003Einterface HasColor {\u003Cbr\u003E Color getColor();\u003Cbr\u003E}\u003Cbr\u003Eclass Colored\u003CT extends HasColor\u003E {\r\n T item;\u003Cbr\u003E public Colored(T item) { this.item = item; }\u003Cbr\u003E public T getItem() { return item; }\r\n\u003Cbr\u003E \u002F\u002F The bound allows you to call a method:\r\n public Color color() { return item.getColor(); }\r\n}\u003Cbr\u003E","\u003Cp\u003ECompound bounds\u003Cbr\u003Eclass Dimension { public int x, y, z; } \u003Cbr\u003E\u002F\u002F Multiple bounds: \r\nclass ColoredDimension\u003CT extends Dimension & HasColor\u003E { \r\n T item; \r\n ColoredDimension(T item) { this.item = item; } \r\n T getItem() { return item; } \r\n Color color() { return item.getColor(); } \r\n int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EBounds and Inheritance\u003Cbr\u003E\r\nclass HoldItem\u003CT\u003E {\r\n T item;\r\n HoldItem(T item) { this.item = item; }\r\n T getItem() { return item; }\r\n}\u003Cbr\u003E\r\nclass Colored2\u003CT extends HasColor\u003E extends HoldItem\u003CT\u003E { \r\n \u002F\u002F some code here...\u003Cbr\u003E Color color() { return item.getColor(); } \r\n}\u003Cbr\u003E\r\nclass ColoredDimension2\u003CT extends Dimension & HasColor\u003E\r\n extends Colored2\u003CT\u003E {\r\n \u002F\u002F some code here...\u003Cbr\u003E int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EPolymorphism and Generics\u003Cbr\u003E\r\nclass Holder\u003CT\u003E {\r\n T item;\r\n void set(T item) { this.item = item; }\r\n T get() { return item; }\r\n}\r\nabstract class Parent { }\u003Cbr\u003Eclass Child extends Parent { }\u003Cbr\u003Eclass AnotherChild extends Parent { }\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CChild\u003E h1 = new Holder\u003CChild\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h2 = new Holder\u003CParent\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h3 = new Holder\u003CChild\u003E(); \u002F\u002F Error\u003Cbr\u003E\u002F\u002F because one could do this:\u003Cbr\u003E\u002F\u002F h3.set(new AnotherChild());\u003Cbr\u003E","\u003Cp\u003EWhy Polymorphism doesn’t work\u003Cbr\u003E\u003Cp\u003Eclass Holder\u003CT\u003E {\r\n T[] items;\u003Cbr\u003E int num = 0;\r\n void add(T item) { this.items[num++] = item;}\r\n T[] get() { return items; }\r\n}\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CInteger\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003EHolder\u003CNumber\u003E reg = h;\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003EInteger i3 = h.get()[2]\u003Cbr\u003ESo Double is a Number but Holder\u003CDouble\u003E is not Holder\u003CNumber\u003E \u003Cbr\u003E\u003Cp\u003EClass case exception Double != Integer\u003Cbr\u003E\u003Cp\u003Eh -\u003E {Integer, Integer, Double}\u003Cbr\u003E\u003Cp\u003EIf polymorphism was allowed this would be legal\u003Cbr\u003E\u003Cp\u003EThis is also legal since Double is a Number\u003Cbr\u003E","\u003Cp\u003EBut you can do this:\u003Cbr\u003E\u003Cp\u003EThis is how you can put different object types in parameterized Holder object:\u003Cbr\u003EHolder\u003CNumber\u003E h = new Holder\u003CNumber\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003ENumber i3 = h.get()[2]\u003Cbr\u003E\u003Cp\u003EBoth Integer and Double are the Numbers\u003Cbr\u003E","\u003Cp\u003EMore Example\u003Cbr\u003Eabstract class Animal { public abstract void check(); }\u003Cbr\u003Eclass Dog extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Dog\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass Cat extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Cat\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003CAnimal\u003E animal) {\u003Cbr\u003E animal.get().check();\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F Error\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F Error\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EGeneric Wildcards (?)\u003Cbr\u003E\u003Cp\u003EThe wildcard provides a polymorphic - like behavior for declaring generics.\u003Cbr\u003E\u003C?\u003E , an unbounded wildcard\u003Cbr\u003E\u003C? extends type\u003E , a wildcard with an upper bound\u003Cbr\u003E\u003C? super type\u003E , a wildcard with a lower bound\u003Cbr\u003E","\u003Cp\u003EUnbounded Wildcards\u003Cbr\u003E\u003Cp\u003EThe unbounded wildcard represents any data type, similar to the \u003C T \u003E syntax. \u003Cbr\u003Epublic static void printList(List\u003C?\u003E list) {\u003Cbr\u003E for(Object x : list) {\u003Cbr\u003E System.out.println(x.toString());\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E...\u003Cbr\u003EArrayList\u003CString\u003E keywords = new ArrayList\u003CString\u003E();\u003Cbr\u003Ekyewords.add(“generic”);\u003Cbr\u003EprintList(keywords);\u003Cbr\u003EUse the ? in situations where you do not need a formal parameter type like \u003C T \u003E\u003Cbr\u003E\u003Cp\u003EData type is not required here\u003Cbr\u003E","\u003Cp\u003EBe careful\u003Cbr\u003E\u003Cp\u003EHolder\u003C?\u003E h = new Holder\u003CString\u003E();\u003Cbr\u003Eh.add(new Object()); \u002F\u002F compile time error\u003Cbr\u003Eh.add(new String()); \u002F\u002F compile time error\u003Cbr\u003E\u002F\u002F one exception!\u003Cbr\u003Eh.add(null); \u002F\u002F null is member of every type\u003Cbr\u003E\u003Cbr\u003EWorking with unbounded wildcards we can only read data, not assign!\u003Cbr\u003E\u003Cbr\u003E","\u003Cp\u003EUpper - Bound Wildcards\u003Cbr\u003E\u003Cp\u003EBounded wildcards put some restrictions on unknown type:\u003Cbr\u003Epublic static void printList(List\u003C? extends Number\u003E list){\u003Cbr\u003E for(Number x : list) {\u003Cbr\u003E System.out.println(x.doubleValue());\u003Cbr\u003E }\u003Cbr\u003E list.add(new Integer(3)); \u002F\u002F compile error\u003Cbr\u003E}\u003Cbr\u003E\u003Cp\u003ENow we know that object is instance of Number\u003Cbr\u003E\u003Cp\u003EBut we still don’t know exact type, so can’t modify list\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? extends Animal\u003E animal) {\u003Cbr\u003E animal.get().check(); \u002F\u002F OK\u003Cbr\u003E animal.set(new Cat()); \u002F\u002F Error: we don’t know exact parameter type of animal\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003ELower Bounded Wildcards\u003Cbr\u003E\u003Cp\u003Ea lower bounded wildcard restricts the unknown type to be a specific type or a super type of that type\u003Cbr\u003EHolder\u003C? super Integer\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(new Integer(1));\u003Cbr\u003EInteger i1 = h.get(); \u002F\u002F compilation error\u003Cbr\u003E\t\t\t\u002F\u002F get returns Object\u003Cbr\u003EInteger i2 = (Integer)h.get(); \u002F\u002F OK\u003Cbr\u003ELower bounded wildcards allow to modify but not read!!\u003Cbr\u003E","\u003Cp\u003EExample\u003Cbr\u003E\u003Cp\u003Epublic static void addNumbers(List\u003C? super Integer\u003E list) {\u003Cbr\u003E for (int i = 1; i \u003C= 10; i++) {\u003Cbr\u003E list.add(i);\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003EList\u003CInteger\u003E i = new ArrayList\u003CInteger\u003E();\u003Cbr\u003EList\u003CNumber\u003E n = new ArrayList\u003CNumber\u003E();\u003Cbr\u003EList\u003CObject\u003E o = new ArrayList\u003CObject\u003E();\u003Cbr\u003E\t\t\u003Cbr\u003EaddNumbers(i);\u003Cbr\u003EaddNumbers(n);\u003Cbr\u003EaddNumbers(o);\u003Cbr\u003EThis works fine\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? super Dog\u003E dog) {\u003Cbr\u003E animal.get().check(); \u002F\u002F Error!\u003Cbr\u003E \u002F\u002F get() returns Object ref\u003Cbr\u003E animal.set(new Dog()); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CAnimal\u003E animal = new Holder\u003CAnimal\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat= new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(animal); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002FError: Cat isn’t super of Dog\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EWhat's the difference?\u003Cbr\u003Evoid check(Holder\u003C?\u003E holder) { }\u003Cbr\u003Evoid check(Holder\u003CObject\u003E holder) { }\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003CObject\u003E obj) {\u003Cbr\u003E obj.set(new Dog());\u003Cbr\u003E obj.set(new Cat());\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CObject\u003E obj = new Holder\u003CObject\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(obj); \u002F\u002F Only Holder\u003CObject\u003E goes here!\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003C?\u003E obj) {\u003Cbr\u003E obj.set(new Dog()); \u002F\u002F Error\u003Cbr\u003E \u002F\u002F Compiler isn't sure that it's really Dog Holder\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CInteger\u003E integer = new Holder\u003CInteger\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(dog); \u002F\u002F OK\u003Cbr\u003E main.check(integer); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E",I,I,"\u003Cp\u003ENaming Conventions for Generics\u003Cbr\u003E\u003Cp\u003EE for an element\u003Cbr\u003EK for a map key\u003Cbr\u003EV for a map value\u003Cbr\u003EN for a number\u003Cbr\u003ET for a generic data type\u003Cbr\u003EUse S , U , V , and so on for multiple types in the same class.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E1) Generics let you enforce compile-time type safety.\u003Cbr\u003EHolder\u003CString\u003E h1 = new Holder\u003CString\u003E();\u003Cbr\u003EHolder h2 = new Holder();\u003Cbr\u003EString s = h1.get(); \u002F\u002F no cast needed\u003Cbr\u003EString s = (String) h2.get(); \u002F\u002F cast required\u003Cbr\u003E2) Generic type information does not exist at runtime — it is for compile-time safety only.\u003Cbr\u003E3) Polymorphic assignment don't apply to the generic type\u003Cbr\u003EHolder\u003CAnimal\u003E h1 = new Holder\u003CDog\u003E(); \u002F\u002F Error\u003Cbr\u003E4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:\u003Cbr\u003Evoid foo(List\u003CDog\u003E d) {} \u002F\u002F can take only \u003CDog\u003E\u003Cbr\u003Evoid foo(List\u003C? extends Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CCollie\u003E\u003Cbr\u003Evoid foo(List\u003C? super Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CAnimal\u003E\u003Cbr\u003E5) When using a wildcard, List\u003C? extends Dog\u003E, the collection can be accessed but not modified.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E6) The generics type identifier can be used in class, method, and variable declarations:\u003Cbr\u003E class Foo\u003Ct\u003E { } \u002F\u002F a class\u003Cbr\u003E T anInstance; \u002F\u002F an instance variable\u003Cbr\u003E Foo(T aRef) {} \u002F\u002F a constructor argument\u003Cbr\u003E void bar(T aRef) {} \u002F\u002F a method argument\u003Cbr\u003E T baz() {} \u002F\u002F a return type\u003Cbr\u003E7) You can use more than one parameterized type in a declaration:\u003Cbr\u003E public class UseTwo\u003CT, X\u003E { }\u003Cbr\u003E8) You can declare a generic method using a type not defined in the class:\u003Cbr\u003E public \u003CT\u003E T returnMe(T t) { return t; }\u003Cbr\u003EReading in Russian\u003Cbr\u003Ehttp:\u002F\u002Fwww.rsdn.ru\u002Farticle\u002Fjava\u002Fgenericsinjava.xml\u003Cbr\u003E"],href:"\u002Finformatika\u002Fgenerics-lecture-73",href_category:"\u002Finformatika",date:1628090801,related:[{id:404222,name:"Научно-техническая информация",href:"\u002Finformatika\u002Fnauchno-tehnicheskaya-informatsiya-1",jpg:"jpg\u002F404222"},{id:478755,name:"Презентация к аттестации учителя информатики",href:"\u002Finformatika\u002Fprezentatsiya-k-attestatsii-uchitelya-informatiki",jpg:"jpg\u002F478755"},{id:4499,name:"Основные компоненты ПК",href:"\u002Finformatika\u002Fosnovnye-komponenty-pk",jpg:"jpg\u002F4499"},{id:184558,name:"Арифметические основы организации ЭВМ",href:"\u002Finformatika\u002Farifmeticheskie-osnovy-organizatsii-evm",jpg:"jpg\u002F184558"},{id:373746,name:"Вёрстка и дизайн газетной статьи",href:"\u002Finformatika\u002Fvyorstka-i-dizayn-gazetnoy-stati",jpg:"jpg\u002F373746"},{id:577279,name:"Алгоритм действий родителей для прохождения регистрации их детей младше\u002Fстарше 14 лет во ФГИС Моя школа",href:"\u002Finformatika\u002Falgoritm-deystviy-roditeley-dlya-prohozhdeniya-registratsii",jpg:"jpg\u002F577279"},{id:12068,name:"Керування правами доступу",href:"\u002Finformatika\u002Fkeruvannya-pravami-dostupu",jpg:"jpg\u002F12068"},{id:403270,name:"Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)",href:"\u002Finformatika\u002Fponyatie-algoritma-svoystva-vidy-tipy-formy",jpg:"jpg\u002F403270"},{id:234266,name:"Взаимодействие клиента и сервера",href:"\u002Finformatika\u002Fvzaimodeystvie-klienta-i-servera",jpg:"jpg\u002F234266"},{id:266792,name:"Как с нуля запустить Онлайн-школу",href:"\u002Finformatika\u002Fkak-s-nulya-zapustit-onlayn-shkolu",jpg:"jpg\u002F266792"},{id:104353,name:"Программа Project Expert",href:"\u002Finformatika\u002Fprogramma-project-expert",jpg:"jpg\u002F104353"},{id:3725,name:"What is cryptocurrency",href:"\u002Finformatika\u002Fwhat-is-cryptocurrency",jpg:"jpg\u002F3725"},{id:1966,name:"История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД",href:"\u002Finformatika\u002Fistoriya-razvitiya-i-pokoleniya-subd-klassifikatsiya",jpg:"jpg\u002F1966"},{id:253599,name:"WORD-тын графикалык мумкіндіктері",href:"\u002Finformatika\u002Fword-tyn-grafikalyk-mumkndkter",jpg:"jpg\u002F253599"},{id:215026,name:"Компьютер как универсальное устройство обработки информации",href:"\u002Finformatika\u002Fkompyuter-kak-universalnoe-ustroystvo-obrabotki-informatsii",jpg:"jpg\u002F215026"},{id:200593,name:"Линейное программирование",href:"\u002Finformatika\u002Flineynoe-programmirovanie-2",jpg:"jpg\u002F200593"},{id:429765,name:"ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области",href:"\u002Finformatika\u002Fou-novoseletskaya-shkola-navigator-dopolnitelnogo-obrazovaniya",jpg:"jpg\u002F429765"},{id:383037,name:"Социальная память. Функция социальной памяти",href:"\u002Finformatika\u002Fsotsialnaya-pamyat-funktsiya-sotsialnoy-pamyati",jpg:"jpg\u002F383037"},{id:160929,name:"Різновиди діаграм та їх форматування",href:"\u002Finformatika\u002Frznovidi-dagram-ta-h-formatuvannya",jpg:"jpg\u002F160929"},{id:266355,name:"Лекция 2. Файлы (текстовые). Массивы",href:"\u002Finformatika\u002Flektsiya-2-fayly-tekstovye-massivy",jpg:"jpg\u002F266355"},{id:610347,name:"3D моделирование в программе Tinkercad",href:"\u002Finformatika\u002F3d-modelirovanie-v-programme-tinkercad",jpg:"jpg\u002F610347"},{id:393791,name:"Load testing with Visual Studio Enterprise 2015",href:"\u002Finformatika\u002Fload-testing-with-visual-studio-enterprise",jpg:"jpg\u002F393791"},{id:114799,name:"Информация, ее свойства. Информация и управление",href:"\u002Finformatika\u002Finformatsiya-ee-svoystva-informatsiya-i-upravlenie",jpg:"jpg\u002F114799"},{id:435506,name:"Информационные технологии в ДОУ",href:"\u002Finformatika\u002Finformatsionnye-tehnologii-v-dou",jpg:"jpg\u002F435506"},{id:439332,name:"Security. The goal",href:"\u002Finformatika\u002Fsecurity-the-goal",jpg:"jpg\u002F439332"},{id:15166,name:"Интернет желісіне жалпы сипаттама",href:"\u002Finformatika\u002Finternet-zhelsne-zhalpy-sipattama",jpg:"jpg\u002F15166"},{id:326320,name:"Особенности работы с информацией в различных типах источников. Лекция 3",href:"\u002Finformatika\u002Fosobennosti-raboty-s-informatsiey-v-razlichnyh",jpg:"jpg\u002F326320"},{id:503963,name:"Презентация к уроку информатики в 5 классе по теме Метод координат",href:"\u002Finformatika\u002Fprezentatsiya-k-uroku-informatiki-v-5-6",jpg:"jpg\u002F503963"}],navigation:{next:"\u002Fliteratura\u002Ftragediya-gyote-faust-2",next_name:"Трагедия Гёте Фауст",prev:"\u002Finformatika\u002Finternet-technologies-2",prev_name:"Internet technologies"}}},categories:{result:[{id:J,ordering:b,name:"Без категории",pseudoname:"uncategorized"},{id:H,ordering:b,name:"Бизнес",pseudoname:"biznes"},{id:146,ordering:b,name:"Образование",pseudoname:"obrazovanie"},{id:149,ordering:b,name:"Финансы",pseudoname:"finansy"},{id:150,ordering:b,name:"Государство",pseudoname:"gosudarstvo"},{id:152,ordering:b,name:"Спорт",pseudoname:"sport"},{id:154,ordering:b,name:"Армия",pseudoname:"armiya"},{id:156,ordering:b,name:"Культурология",pseudoname:"kulturologiya"},{id:157,ordering:b,name:"Еда и кулинария",pseudoname:"eda-i-kulinariya"},{id:158,ordering:b,name:"Лингвистика",pseudoname:"lingvistika"},{id:163,ordering:b,name:"Черчение",pseudoname:"cherchenie"},{id:164,ordering:b,name:"Физкультура",pseudoname:"fizkultura"},{id:165,ordering:b,name:"ИЗО",pseudoname:"izo"},{id:166,ordering:b,name:"Психология",pseudoname:"psihologiya"},{id:116,ordering:J,name:"Английский язык",pseudoname:"angliyskiy-yazyk"},{id:108,ordering:2,name:"Астрономия",pseudoname:"astronomiya"},{id:104,ordering:3,name:"Алгебра",pseudoname:"algebra"},{id:106,ordering:4,name:"Биология",pseudoname:"biologiya"},{id:142,ordering:5,name:"География",pseudoname:"geografiya"},{id:141,ordering:6,name:"Геометрия",pseudoname:"geometria"},{id:123,ordering:7,name:"Детские презентации",pseudoname:"detskie-prezentatsii"},{id:107,ordering:8,name:G,pseudoname:"informatika"},{id:109,ordering:9,name:"История",pseudoname:"istoriya"},{id:139,ordering:10,name:"Литература",pseudoname:"literatura"},{id:119,ordering:11,name:"Маркетинг",pseudoname:"marketing"},{id:114,ordering:12,name:"Математика",pseudoname:"matematika"},{id:138,ordering:h,name:"Медицина",pseudoname:"medetsina"},{id:118,ordering:14,name:"Менеджмент",pseudoname:"menedzhment"},{id:137,ordering:15,name:"Музыка",pseudoname:"muzyka"},{id:136,ordering:16,name:"МХК",pseudoname:"mhk"},{id:130,ordering:17,name:"Немецкий язык",pseudoname:"nemetskiy-yazyk"},{id:105,ordering:18,name:"ОБЖ",pseudoname:"obzh"},{id:133,ordering:19,name:"Обществознание ",pseudoname:"obshchestvoznanie"},{id:132,ordering:20,name:"Окружающий мир ",pseudoname:"okruzhayushchiy-mir"},{id:131,ordering:21,name:"Педагогика ",pseudoname:"pedagogika"},{id:129,ordering:22,name:"Русский язык",pseudoname:"russkiy-yazyk"},{id:128,ordering:24,name:"Технология",pseudoname:"tehnologiya"},{id:127,ordering:25,name:"Физика",pseudoname:"fizika"},{id:126,ordering:26,name:"Философия",pseudoname:"filosofiya"},{id:125,ordering:27,name:"Химия",pseudoname:"himiya"},{id:124,ordering:29,name:"Экология",pseudoname:"ekologiya"},{id:121,ordering:30,name:"Экономика",pseudoname:"ekonomika"},{id:120,ordering:31,name:"Юриспруденция",pseudoname:"yurisprudentsiya"}]}},state:{},_errors:{},serverRendered:e,config:{public:{SITE_NAME:K,SITE_HOST:"mypreza.com",SITE_LANG:L,API_BASE_URL:"https:\u002F\u002Fmypreza.com\u002Fapi\u002F",pwaManifest:{name:K,short_name:a,description:a,lang:L,start_url:"\u002F?standalone=true",display:"standalone",background_color:j,theme_color:"#000000",icons:[{src:"\u002F_nuxt\u002Ficons\u002F64x64.f2a6e93d.png",type:d,sizes:M,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F64x64.maskable.f2a6e93d.png",type:d,sizes:M,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F120x120.f2a6e93d.png",type:d,sizes:N,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F120x120.maskable.f2a6e93d.png",type:d,sizes:N,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F144x144.f2a6e93d.png",type:d,sizes:O,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F144x144.maskable.f2a6e93d.png",type:d,sizes:O,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F152x152.f2a6e93d.png",type:d,sizes:P,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F152x152.maskable.f2a6e93d.png",type:d,sizes:P,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F192x192.f2a6e93d.png",type:d,sizes:Q,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F192x192.maskable.f2a6e93d.png",type:d,sizes:Q,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F384x384.f2a6e93d.png",type:d,sizes:R,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F384x384.maskable.f2a6e93d.png",type:d,sizes:R,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F512x512.f2a6e93d.png",type:d,sizes:S,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F512x512.maskable.f2a6e93d.png",type:d,sizes:S,purpose:g}]},yandexMetrika:{id:"85004146",metrikaUrl:"https:\u002F\u002Fmc.yandex.ru\u002Fmetrika\u002Ftag.js",accurateTrackBounce:e,childIframe:c,clickmap:c,defer:c,useRuntimeConfig:e,trackHash:c,trackLinks:e,type:b,webvisor:c,triggerEvent:c,consoleLog:e,partytown:c,isDev:c}},app:{baseURL:"\u002F",buildAssetsDir:"\u002F_nuxt\u002F",cdnURL:a}},pinia:{app:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F,token:a}}}}("",0,false,"image\u002Fpng",true,"any","maskable",13,"#d53032","#ffffff","Generics. (Lecture 7.3)","Учебные презентации","Презентации в PowerPoint на разные темы","Презентации, проекты, доклады в PowerPoint на разные темы для учебы","Презентация, на тему, урок, класс, PowerPoint, скачати презентацію, фон, шаблон, доклад, проект.","images\u002Fdata\u002Flogo.png",185,40,720,480,"6LeioWIpAAAAAGqMN4KqMVIkekcMW7fBKHjXCd-a","2503267","[e-mail]","h3a","text","none","h3","category","both",80,800,"\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fes5-shims\u002F0.0.2\u002Fes5-shims.min.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fshare2\u002Fshare.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cdiv class=\"ya-share2\" data-services=\"collections,gplus,vkontakte,facebook,odnoklassniki,gplus,twitter,moimir\" data-counter=\"\"\u003E\u003C\u002Fdiv\u003E","Информатика",144,"\u003Cp\u003EWhich will compile?\u003Cbr\u003E1) List\u003C?\u003E list = new ArrayList\u003CDog\u003E();\u003Cbr\u003E2) List\u003C? extends Animal\u003E aList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E3) List\u003C?\u003E foo = new ArrayList\u003C? extends Animal\u003E();\u003Cbr\u003E4) List\u003C? extends Dog\u003E cList = new ArrayList\u003CInteger\u003E();\u003Cbr\u003E5) List\u003C? super Dog\u003E bList = new ArrayList\u003CAnimal\u003E();\u003Cbr\u003E6) List\u003C? super Animal\u003E dList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E",1,"Mypreza","ru","64x64","120x120","144x144","152x152","192x192","384x384","512x512")) obj.set(new Cat());
}
public static void main(String[] args) {
Holder
obj = new Holder
();
Main main = new Main();
main.check(obj); // Only Holder
goes here!
}
}
Слайд 37
There IS a huge difference!
class Main {
void check(Holder
obj) {
obj.set(new Dog());
// Error
// Compiler isn't sure that it's really Dog Holder
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
integer = new Holder
();
Main main = new Main();
main.check(dog); // OK
main.check(integer); // OK
}
}
Слайд 38
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 39
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 40
Naming Conventions for Generics
E for an element
K for a map key
V for a
map value
N for a number
T for a generic data type
Use S , U , V , and so on for multiple types in the same class.
Слайд 41
Summary
1) Generics let you enforce compile-time type safety.
Holder
h1 = new Holder
();
Holder h2 =
new Holder();
String s = h1.get(); // no cast needed
String s = (String) h2.get(); // cast required
2) Generic type information does not exist at runtime — it is for compile-time safety only.
3) Polymorphic assignment don't apply to the generic type
Holder
h1 = new Holder
(); // Error
4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:
void foo(List
d) {} // can take only
void foo(List
) {} // take a
or
void foo(List
) {} // take a
or
5) When using a wildcard, List
, the collection can be accessed but not modified.
Имя файла: Generics.-(Lecture-7.3).pptx
Количество просмотров: 144
Количество скачиваний: 0
Скачать
- Предыдущая
Internet technologies
Следующая -
Трагедия Гёте Фауст
Похожие презентации
Научно-техническая информация
Презентация к аттестации учителя информатики
Основные компоненты ПК
Арифметические основы организации ЭВМ
Вёрстка и дизайн газетной статьи
Алгоритм действий родителей для прохождения регистрации их детей младше/старше 14 лет во ФГИС Моя школа
Керування правами доступу
Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)
Взаимодействие клиента и сервера
Как с нуля запустить Онлайн-школу
Программа Project Expert
What is cryptocurrency
История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД
WORD-тын графикалык мумкіндіктері
Компьютер как универсальное устройство обработки информации
Линейное программирование
ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области
Социальная память. Функция социальной памяти
Різновиди діаграм та їх форматування
Лекция 2. Файлы (текстовые). Массивы
3D моделирование в программе Tinkercad
Load testing with Visual Studio Enterprise 2015
Информация, ее свойства. Информация и управление
Информационные технологии в ДОУ
Security. The goal
Интернет желісіне жалпы сипаттама
Особенности работы с информацией в различных типах источников. Лекция 3
Презентация к уроку информатики в 5 классе по теме Метод координат
Обратная связь
Email:
Нажмите что бы посмотреть
window.__NUXT__=(function(a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S){return {data:{meta:{result:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F}},item:{result:{id:139284,name:k,category:G,count:42,jpg:"jpg\u002F139284",hits:H,download:b,h1:"Generics. (Lecture 7.3) презентация",meta:{h1:k,title:k,description:"Generics. (Lecture 7.3) презентация на тему, доклад, Информатика",keywords:"Generics. (Lecture 7.3), презентация, доклад, проект, скачать, на тему, PowerPoint, урок, класс, школа, Информатика",download_link:a},text:"Вы можете изучить и скачать доклад-презентацию на тему Презентация на тему Generics. (Lecture 7.3) из раздела Информатика. Презентация на заданную тему содержит 42 слайдов. Для просмотра воспользуйтесь проигрывателем, если материал оказался полезным для Вас - поделитесь им с друзьями с помощью социальных кнопок и добавьте наш сайт презентаций в закладки!",seo_text:"\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E \u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E",file:"Generics.-(Lecture-7.3).pptx",texts:["\u003Cp\u003EGenerics\u003Cbr\u003E","\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E","\u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E","\u003Cp\u003EA class that holds a single object\u003Cbr\u003Eclass Automobile {}\u003Cbr\u003Epublic class Holder1 {\u003Cbr\u003E private Automobile a;\u003Cbr\u003E public Holder1(Automobile a) {\u003Cbr\u003E this.a = a;\u003Cbr\u003E }\u003Cbr\u003E Automobile get() { return a; }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EA class that holds an Object\u003Cbr\u003Epublic class Holder2 { \r\n private Object a; \r\n public Holder2(Object a) { this.a = a; } \r\n\r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder2 h2 = new Holder2(new Automobile()); \r\n Automobile a = (Automobile) h2.get(); \r\n h2.set(\"Not an Automobile\"); \r\n String s = (String) h2.get(); \r\n h2.set(1); \u002F\u002F Autoboxes to Integer \r\n Integer x = (Integer) h2.get(); \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003ESimple generic class\u003Cbr\u003E\r\npublic class Holder3\u003CT\u003E { \u003Cbr\u003E private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder3\u003CAutomobile\u003E h3 =\r\n new Holder3\u003CAutomobile\u003E(new Automobile()); \r\n Automobile a = h3.get(); \u002F\u002F No cast needed \r\n \u002F\u002F h3.set(\"Not an Automobile\"); \u002F\u002F Error \r\n \u002F\u002F h3.set(1); \u002F\u002F Error \r\n } \r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Types and Methods\u003Cbr\u003E\u003Cp\u003EThere can be:\u003Cbr\u003EGeneric classes\u003Cbr\u003EGeneric interfaces\u003Cbr\u003EGeneric methods\u003Cbr\u003EBounded generic types\u003Cbr\u003EGeneric wildcards\u003Cbr\u003E","\u003Cp\u003EThe core idea of Java generics: You tell it what type you want to use, and it takes care of the details.\u003Cbr\u003E","\u003Cp\u003EType erasure\u003Cbr\u003E\u003Cp\u003EJava generics are implemented using type erasure. This means that any specific type information is erased when you compile your code.\u003Cbr\u003E","\u003Cp\u003EHow type erasure works?\u003Cbr\u003E\u003Cp\u003Epublic class Holder3\u003CT\u003E { \r\n private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3\u003CLong\u003E h3 =\u003Cbr\u003E new Holder3\u003CLong\u003E(1L);\u003Cbr\u003ELong n = h3.get();\u003Cbr\u003E\u003Cp\u003Epublic class Holder3 { \r\n private Object a; \r\n\r\n public Holder3(Object a) { this.a = a; } \r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3 h3 = new Holder3(1L);\u003Cbr\u003ELong n = (Long) h3.get();\u003Cbr\u003E","\u003Cp\u003ECompensating for erasure\r\n\r\npublic class Erased\u003CT\u003E {\r\n private final int SIZE = 100;\r\n\r\n public static void f(Object arg) {\r\n if(arg instanceof T) {} \u002F\u002F Error\r\n T var = new T(); \u002F\u002F Error\r\n T[] array = new T[SIZE]; \u002F\u002F Error\r\n T[] array = (T[])new Object[SIZE]; \u002F\u002F Unchecked \t\t\t\t\t\t\twarning\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric class with two types\r\n\r\npublic class TwoTuple\u003CA, B\u003E { \r\n public final A first; \r\n public final B second; \r\n\r\n public TwoTuple(A a, B b) { first = a; second = b; } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \")\"; \r\n } \r\n} \u003Cbr\u003E","\u003Cp\u003EYou cannot use primitives as type parameters!\r\n\r\nTwoTuple\u003CString, Integer\u003E ttsi = new TwoTuple\u003CString, Integer\u003E(\"hi\", 47);\r\n\r\nbut not\r\n\r\nTwoTuple\u003Cdouble, int\u003E ttdi = new TwoTuple\u003Cdouble, int\u003E(47.0, 47);\u003Cbr\u003E","\u003Cp\u003EInheritance with generic classes\r\n\r\npublic class ThreeTuple\u003CA, B, C\u003E extends TwoTuple\u003CA, B\u003E { \r\n public final C third; \r\n\r\n public ThreeTuple(A a, B b, C c) { \r\n super(a, b); \r\n third = c; \r\n } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \", \" +\r\n third +\")\"; \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric interface\u003Cbr\u003E\r\npublic interface Generator\u003CT\u003E { T next(); }\r\n\r\npublic class Fibonacci implements Generator\u003CInteger\u003E {\r\n private int count = 0;\r\n public Integer next() { return fib(count++); }\u003Cbr\u003E \u003Cbr\u003E ...\u003Cbr\u003E\r\n public static void main(String[] args) {\r\n Fibonacci gen = new Fibonacci();\r\n for(int i = 0; i \u003C 18; i++)\r\n System.out.print(gen.next() + \" \");\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Methods\r\n\r\npublic class GenericMethods {\r\n public \u003CT\u003E void f(T x) {\r\n System.out.println(x.getClass().getName());\r\n }\r\n public static void main(String[] args) {\r\n GenericMethods gm = new GenericMethods();\r\n gm.f(\"\");\r\n gm.f(1);\r\n gm.f(1.0);\r\n gm.f('c');\r\n gm.f(new String[] {“H”, “W”});\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EThe Syntax for Invoking a Generic Method\u003Cbr\u003EGenerics have an optional syntax for specifying the type for a generic method. You can place the data type of the generic in angle brackets, \u003C \u003E , after the dot operator and before the method call.\u003Cbr\u003E\r\n gm.\u003CString\u003Ef(“a string object”);\r\n gm.\u003CInteger\u003Ef(1);\r\n gm.\u003CDouble\u003Ef(1.0);\r\n gm.\u003CChar\u003Ef('c');\u003Cbr\u003E gm.\u003CString[]\u003Ef(new String[] {“H”, “W”});\u003Cbr\u003EThe syntax makes the code more readable and also gives you control over the generic type in situations where the type might not be obvious.\u003Cbr\u003E","\u003Cp\u003ELeveraging type argument inference \r\n\r\npublic class Tuple {\r\n public static \u003CA,B\u003E TwoTuple\u003CA,B\u003E tuple(A a, B b) {\r\n return new TwoTuple\u003CA,B\u003E(a, b);\r\n }\r\n public static \u003CA,B,C\u003E ThreeTuple\u003CA,B,C\u003E tuple(A a,B b,C c) {\r\n return new ThreeTuple\u003CA,B,C\u003E(a, b, c);\r\n }\r\n}\r\n...\r\nTwoTuple\u003CString, Integer\u003E ttsi = Tuple.tuple(“hi”, 47);\r\nThreeTuple\u003CString,Integer,Double\u003E ttsid=Tuple.tuple(“hi”,47,47.0);\u003Cbr\u003E","\u003Cp\u003EAnonymous inner classes\r\n\r\npublic interface Generator\u003CT\u003E { T next(); } \r\n\r\nclass Customer { \r\n private Customer() {} \r\n\r\n public static Generator\u003CCustomer\u003E generator() { \r\n return new Generator\u003CCustomer\u003E() { \r\n public Customer next() { return new Customer(); } \r\n }; \r\n } \r\n} \r\n...\r\nCustomer customer1 = Customer.generator().next();\r\nCustomer customer2 = Customer.generator().next();\u003Cbr\u003E","\u003Cp\u003EBounded Generic Types\u003Cbr\u003EBecause erasure removes type information, the only methods you can call for an unbounded generic parameter are those available for Object. Bounds allow you to place constraints on the parameter types. Important effect is that you can call methods that are in your bound types.\u003Cbr\u003Einterface HasColor {\u003Cbr\u003E Color getColor();\u003Cbr\u003E}\u003Cbr\u003Eclass Colored\u003CT extends HasColor\u003E {\r\n T item;\u003Cbr\u003E public Colored(T item) { this.item = item; }\u003Cbr\u003E public T getItem() { return item; }\r\n\u003Cbr\u003E \u002F\u002F The bound allows you to call a method:\r\n public Color color() { return item.getColor(); }\r\n}\u003Cbr\u003E","\u003Cp\u003ECompound bounds\u003Cbr\u003Eclass Dimension { public int x, y, z; } \u003Cbr\u003E\u002F\u002F Multiple bounds: \r\nclass ColoredDimension\u003CT extends Dimension & HasColor\u003E { \r\n T item; \r\n ColoredDimension(T item) { this.item = item; } \r\n T getItem() { return item; } \r\n Color color() { return item.getColor(); } \r\n int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EBounds and Inheritance\u003Cbr\u003E\r\nclass HoldItem\u003CT\u003E {\r\n T item;\r\n HoldItem(T item) { this.item = item; }\r\n T getItem() { return item; }\r\n}\u003Cbr\u003E\r\nclass Colored2\u003CT extends HasColor\u003E extends HoldItem\u003CT\u003E { \r\n \u002F\u002F some code here...\u003Cbr\u003E Color color() { return item.getColor(); } \r\n}\u003Cbr\u003E\r\nclass ColoredDimension2\u003CT extends Dimension & HasColor\u003E\r\n extends Colored2\u003CT\u003E {\r\n \u002F\u002F some code here...\u003Cbr\u003E int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EPolymorphism and Generics\u003Cbr\u003E\r\nclass Holder\u003CT\u003E {\r\n T item;\r\n void set(T item) { this.item = item; }\r\n T get() { return item; }\r\n}\r\nabstract class Parent { }\u003Cbr\u003Eclass Child extends Parent { }\u003Cbr\u003Eclass AnotherChild extends Parent { }\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CChild\u003E h1 = new Holder\u003CChild\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h2 = new Holder\u003CParent\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h3 = new Holder\u003CChild\u003E(); \u002F\u002F Error\u003Cbr\u003E\u002F\u002F because one could do this:\u003Cbr\u003E\u002F\u002F h3.set(new AnotherChild());\u003Cbr\u003E","\u003Cp\u003EWhy Polymorphism doesn’t work\u003Cbr\u003E\u003Cp\u003Eclass Holder\u003CT\u003E {\r\n T[] items;\u003Cbr\u003E int num = 0;\r\n void add(T item) { this.items[num++] = item;}\r\n T[] get() { return items; }\r\n}\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CInteger\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003EHolder\u003CNumber\u003E reg = h;\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003EInteger i3 = h.get()[2]\u003Cbr\u003ESo Double is a Number but Holder\u003CDouble\u003E is not Holder\u003CNumber\u003E \u003Cbr\u003E\u003Cp\u003EClass case exception Double != Integer\u003Cbr\u003E\u003Cp\u003Eh -\u003E {Integer, Integer, Double}\u003Cbr\u003E\u003Cp\u003EIf polymorphism was allowed this would be legal\u003Cbr\u003E\u003Cp\u003EThis is also legal since Double is a Number\u003Cbr\u003E","\u003Cp\u003EBut you can do this:\u003Cbr\u003E\u003Cp\u003EThis is how you can put different object types in parameterized Holder object:\u003Cbr\u003EHolder\u003CNumber\u003E h = new Holder\u003CNumber\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003ENumber i3 = h.get()[2]\u003Cbr\u003E\u003Cp\u003EBoth Integer and Double are the Numbers\u003Cbr\u003E","\u003Cp\u003EMore Example\u003Cbr\u003Eabstract class Animal { public abstract void check(); }\u003Cbr\u003Eclass Dog extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Dog\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass Cat extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Cat\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003CAnimal\u003E animal) {\u003Cbr\u003E animal.get().check();\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F Error\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F Error\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EGeneric Wildcards (?)\u003Cbr\u003E\u003Cp\u003EThe wildcard provides a polymorphic - like behavior for declaring generics.\u003Cbr\u003E\u003C?\u003E , an unbounded wildcard\u003Cbr\u003E\u003C? extends type\u003E , a wildcard with an upper bound\u003Cbr\u003E\u003C? super type\u003E , a wildcard with a lower bound\u003Cbr\u003E","\u003Cp\u003EUnbounded Wildcards\u003Cbr\u003E\u003Cp\u003EThe unbounded wildcard represents any data type, similar to the \u003C T \u003E syntax. \u003Cbr\u003Epublic static void printList(List\u003C?\u003E list) {\u003Cbr\u003E for(Object x : list) {\u003Cbr\u003E System.out.println(x.toString());\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E...\u003Cbr\u003EArrayList\u003CString\u003E keywords = new ArrayList\u003CString\u003E();\u003Cbr\u003Ekyewords.add(“generic”);\u003Cbr\u003EprintList(keywords);\u003Cbr\u003EUse the ? in situations where you do not need a formal parameter type like \u003C T \u003E\u003Cbr\u003E\u003Cp\u003EData type is not required here\u003Cbr\u003E","\u003Cp\u003EBe careful\u003Cbr\u003E\u003Cp\u003EHolder\u003C?\u003E h = new Holder\u003CString\u003E();\u003Cbr\u003Eh.add(new Object()); \u002F\u002F compile time error\u003Cbr\u003Eh.add(new String()); \u002F\u002F compile time error\u003Cbr\u003E\u002F\u002F one exception!\u003Cbr\u003Eh.add(null); \u002F\u002F null is member of every type\u003Cbr\u003E\u003Cbr\u003EWorking with unbounded wildcards we can only read data, not assign!\u003Cbr\u003E\u003Cbr\u003E","\u003Cp\u003EUpper - Bound Wildcards\u003Cbr\u003E\u003Cp\u003EBounded wildcards put some restrictions on unknown type:\u003Cbr\u003Epublic static void printList(List\u003C? extends Number\u003E list){\u003Cbr\u003E for(Number x : list) {\u003Cbr\u003E System.out.println(x.doubleValue());\u003Cbr\u003E }\u003Cbr\u003E list.add(new Integer(3)); \u002F\u002F compile error\u003Cbr\u003E}\u003Cbr\u003E\u003Cp\u003ENow we know that object is instance of Number\u003Cbr\u003E\u003Cp\u003EBut we still don’t know exact type, so can’t modify list\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? extends Animal\u003E animal) {\u003Cbr\u003E animal.get().check(); \u002F\u002F OK\u003Cbr\u003E animal.set(new Cat()); \u002F\u002F Error: we don’t know exact parameter type of animal\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003ELower Bounded Wildcards\u003Cbr\u003E\u003Cp\u003Ea lower bounded wildcard restricts the unknown type to be a specific type or a super type of that type\u003Cbr\u003EHolder\u003C? super Integer\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(new Integer(1));\u003Cbr\u003EInteger i1 = h.get(); \u002F\u002F compilation error\u003Cbr\u003E\t\t\t\u002F\u002F get returns Object\u003Cbr\u003EInteger i2 = (Integer)h.get(); \u002F\u002F OK\u003Cbr\u003ELower bounded wildcards allow to modify but not read!!\u003Cbr\u003E","\u003Cp\u003EExample\u003Cbr\u003E\u003Cp\u003Epublic static void addNumbers(List\u003C? super Integer\u003E list) {\u003Cbr\u003E for (int i = 1; i \u003C= 10; i++) {\u003Cbr\u003E list.add(i);\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003EList\u003CInteger\u003E i = new ArrayList\u003CInteger\u003E();\u003Cbr\u003EList\u003CNumber\u003E n = new ArrayList\u003CNumber\u003E();\u003Cbr\u003EList\u003CObject\u003E o = new ArrayList\u003CObject\u003E();\u003Cbr\u003E\t\t\u003Cbr\u003EaddNumbers(i);\u003Cbr\u003EaddNumbers(n);\u003Cbr\u003EaddNumbers(o);\u003Cbr\u003EThis works fine\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? super Dog\u003E dog) {\u003Cbr\u003E animal.get().check(); \u002F\u002F Error!\u003Cbr\u003E \u002F\u002F get() returns Object ref\u003Cbr\u003E animal.set(new Dog()); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CAnimal\u003E animal = new Holder\u003CAnimal\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat= new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(animal); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002FError: Cat isn’t super of Dog\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EWhat's the difference?\u003Cbr\u003Evoid check(Holder\u003C?\u003E holder) { }\u003Cbr\u003Evoid check(Holder\u003CObject\u003E holder) { }\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003CObject\u003E obj) {\u003Cbr\u003E obj.set(new Dog());\u003Cbr\u003E obj.set(new Cat());\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CObject\u003E obj = new Holder\u003CObject\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(obj); \u002F\u002F Only Holder\u003CObject\u003E goes here!\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003C?\u003E obj) {\u003Cbr\u003E obj.set(new Dog()); \u002F\u002F Error\u003Cbr\u003E \u002F\u002F Compiler isn't sure that it's really Dog Holder\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CInteger\u003E integer = new Holder\u003CInteger\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(dog); \u002F\u002F OK\u003Cbr\u003E main.check(integer); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E",I,I,"\u003Cp\u003ENaming Conventions for Generics\u003Cbr\u003E\u003Cp\u003EE for an element\u003Cbr\u003EK for a map key\u003Cbr\u003EV for a map value\u003Cbr\u003EN for a number\u003Cbr\u003ET for a generic data type\u003Cbr\u003EUse S , U , V , and so on for multiple types in the same class.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E1) Generics let you enforce compile-time type safety.\u003Cbr\u003EHolder\u003CString\u003E h1 = new Holder\u003CString\u003E();\u003Cbr\u003EHolder h2 = new Holder();\u003Cbr\u003EString s = h1.get(); \u002F\u002F no cast needed\u003Cbr\u003EString s = (String) h2.get(); \u002F\u002F cast required\u003Cbr\u003E2) Generic type information does not exist at runtime — it is for compile-time safety only.\u003Cbr\u003E3) Polymorphic assignment don't apply to the generic type\u003Cbr\u003EHolder\u003CAnimal\u003E h1 = new Holder\u003CDog\u003E(); \u002F\u002F Error\u003Cbr\u003E4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:\u003Cbr\u003Evoid foo(List\u003CDog\u003E d) {} \u002F\u002F can take only \u003CDog\u003E\u003Cbr\u003Evoid foo(List\u003C? extends Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CCollie\u003E\u003Cbr\u003Evoid foo(List\u003C? super Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CAnimal\u003E\u003Cbr\u003E5) When using a wildcard, List\u003C? extends Dog\u003E, the collection can be accessed but not modified.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E6) The generics type identifier can be used in class, method, and variable declarations:\u003Cbr\u003E class Foo\u003Ct\u003E { } \u002F\u002F a class\u003Cbr\u003E T anInstance; \u002F\u002F an instance variable\u003Cbr\u003E Foo(T aRef) {} \u002F\u002F a constructor argument\u003Cbr\u003E void bar(T aRef) {} \u002F\u002F a method argument\u003Cbr\u003E T baz() {} \u002F\u002F a return type\u003Cbr\u003E7) You can use more than one parameterized type in a declaration:\u003Cbr\u003E public class UseTwo\u003CT, X\u003E { }\u003Cbr\u003E8) You can declare a generic method using a type not defined in the class:\u003Cbr\u003E public \u003CT\u003E T returnMe(T t) { return t; }\u003Cbr\u003EReading in Russian\u003Cbr\u003Ehttp:\u002F\u002Fwww.rsdn.ru\u002Farticle\u002Fjava\u002Fgenericsinjava.xml\u003Cbr\u003E"],href:"\u002Finformatika\u002Fgenerics-lecture-73",href_category:"\u002Finformatika",date:1628090801,related:[{id:404222,name:"Научно-техническая информация",href:"\u002Finformatika\u002Fnauchno-tehnicheskaya-informatsiya-1",jpg:"jpg\u002F404222"},{id:478755,name:"Презентация к аттестации учителя информатики",href:"\u002Finformatika\u002Fprezentatsiya-k-attestatsii-uchitelya-informatiki",jpg:"jpg\u002F478755"},{id:4499,name:"Основные компоненты ПК",href:"\u002Finformatika\u002Fosnovnye-komponenty-pk",jpg:"jpg\u002F4499"},{id:184558,name:"Арифметические основы организации ЭВМ",href:"\u002Finformatika\u002Farifmeticheskie-osnovy-organizatsii-evm",jpg:"jpg\u002F184558"},{id:373746,name:"Вёрстка и дизайн газетной статьи",href:"\u002Finformatika\u002Fvyorstka-i-dizayn-gazetnoy-stati",jpg:"jpg\u002F373746"},{id:577279,name:"Алгоритм действий родителей для прохождения регистрации их детей младше\u002Fстарше 14 лет во ФГИС Моя школа",href:"\u002Finformatika\u002Falgoritm-deystviy-roditeley-dlya-prohozhdeniya-registratsii",jpg:"jpg\u002F577279"},{id:12068,name:"Керування правами доступу",href:"\u002Finformatika\u002Fkeruvannya-pravami-dostupu",jpg:"jpg\u002F12068"},{id:403270,name:"Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)",href:"\u002Finformatika\u002Fponyatie-algoritma-svoystva-vidy-tipy-formy",jpg:"jpg\u002F403270"},{id:234266,name:"Взаимодействие клиента и сервера",href:"\u002Finformatika\u002Fvzaimodeystvie-klienta-i-servera",jpg:"jpg\u002F234266"},{id:266792,name:"Как с нуля запустить Онлайн-школу",href:"\u002Finformatika\u002Fkak-s-nulya-zapustit-onlayn-shkolu",jpg:"jpg\u002F266792"},{id:104353,name:"Программа Project Expert",href:"\u002Finformatika\u002Fprogramma-project-expert",jpg:"jpg\u002F104353"},{id:3725,name:"What is cryptocurrency",href:"\u002Finformatika\u002Fwhat-is-cryptocurrency",jpg:"jpg\u002F3725"},{id:1966,name:"История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД",href:"\u002Finformatika\u002Fistoriya-razvitiya-i-pokoleniya-subd-klassifikatsiya",jpg:"jpg\u002F1966"},{id:253599,name:"WORD-тын графикалык мумкіндіктері",href:"\u002Finformatika\u002Fword-tyn-grafikalyk-mumkndkter",jpg:"jpg\u002F253599"},{id:215026,name:"Компьютер как универсальное устройство обработки информации",href:"\u002Finformatika\u002Fkompyuter-kak-universalnoe-ustroystvo-obrabotki-informatsii",jpg:"jpg\u002F215026"},{id:200593,name:"Линейное программирование",href:"\u002Finformatika\u002Flineynoe-programmirovanie-2",jpg:"jpg\u002F200593"},{id:429765,name:"ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области",href:"\u002Finformatika\u002Fou-novoseletskaya-shkola-navigator-dopolnitelnogo-obrazovaniya",jpg:"jpg\u002F429765"},{id:383037,name:"Социальная память. Функция социальной памяти",href:"\u002Finformatika\u002Fsotsialnaya-pamyat-funktsiya-sotsialnoy-pamyati",jpg:"jpg\u002F383037"},{id:160929,name:"Різновиди діаграм та їх форматування",href:"\u002Finformatika\u002Frznovidi-dagram-ta-h-formatuvannya",jpg:"jpg\u002F160929"},{id:266355,name:"Лекция 2. Файлы (текстовые). Массивы",href:"\u002Finformatika\u002Flektsiya-2-fayly-tekstovye-massivy",jpg:"jpg\u002F266355"},{id:610347,name:"3D моделирование в программе Tinkercad",href:"\u002Finformatika\u002F3d-modelirovanie-v-programme-tinkercad",jpg:"jpg\u002F610347"},{id:393791,name:"Load testing with Visual Studio Enterprise 2015",href:"\u002Finformatika\u002Fload-testing-with-visual-studio-enterprise",jpg:"jpg\u002F393791"},{id:114799,name:"Информация, ее свойства. Информация и управление",href:"\u002Finformatika\u002Finformatsiya-ee-svoystva-informatsiya-i-upravlenie",jpg:"jpg\u002F114799"},{id:435506,name:"Информационные технологии в ДОУ",href:"\u002Finformatika\u002Finformatsionnye-tehnologii-v-dou",jpg:"jpg\u002F435506"},{id:439332,name:"Security. The goal",href:"\u002Finformatika\u002Fsecurity-the-goal",jpg:"jpg\u002F439332"},{id:15166,name:"Интернет желісіне жалпы сипаттама",href:"\u002Finformatika\u002Finternet-zhelsne-zhalpy-sipattama",jpg:"jpg\u002F15166"},{id:326320,name:"Особенности работы с информацией в различных типах источников. Лекция 3",href:"\u002Finformatika\u002Fosobennosti-raboty-s-informatsiey-v-razlichnyh",jpg:"jpg\u002F326320"},{id:503963,name:"Презентация к уроку информатики в 5 классе по теме Метод координат",href:"\u002Finformatika\u002Fprezentatsiya-k-uroku-informatiki-v-5-6",jpg:"jpg\u002F503963"}],navigation:{next:"\u002Fliteratura\u002Ftragediya-gyote-faust-2",next_name:"Трагедия Гёте Фауст",prev:"\u002Finformatika\u002Finternet-technologies-2",prev_name:"Internet technologies"}}},categories:{result:[{id:J,ordering:b,name:"Без категории",pseudoname:"uncategorized"},{id:H,ordering:b,name:"Бизнес",pseudoname:"biznes"},{id:146,ordering:b,name:"Образование",pseudoname:"obrazovanie"},{id:149,ordering:b,name:"Финансы",pseudoname:"finansy"},{id:150,ordering:b,name:"Государство",pseudoname:"gosudarstvo"},{id:152,ordering:b,name:"Спорт",pseudoname:"sport"},{id:154,ordering:b,name:"Армия",pseudoname:"armiya"},{id:156,ordering:b,name:"Культурология",pseudoname:"kulturologiya"},{id:157,ordering:b,name:"Еда и кулинария",pseudoname:"eda-i-kulinariya"},{id:158,ordering:b,name:"Лингвистика",pseudoname:"lingvistika"},{id:163,ordering:b,name:"Черчение",pseudoname:"cherchenie"},{id:164,ordering:b,name:"Физкультура",pseudoname:"fizkultura"},{id:165,ordering:b,name:"ИЗО",pseudoname:"izo"},{id:166,ordering:b,name:"Психология",pseudoname:"psihologiya"},{id:116,ordering:J,name:"Английский язык",pseudoname:"angliyskiy-yazyk"},{id:108,ordering:2,name:"Астрономия",pseudoname:"astronomiya"},{id:104,ordering:3,name:"Алгебра",pseudoname:"algebra"},{id:106,ordering:4,name:"Биология",pseudoname:"biologiya"},{id:142,ordering:5,name:"География",pseudoname:"geografiya"},{id:141,ordering:6,name:"Геометрия",pseudoname:"geometria"},{id:123,ordering:7,name:"Детские презентации",pseudoname:"detskie-prezentatsii"},{id:107,ordering:8,name:G,pseudoname:"informatika"},{id:109,ordering:9,name:"История",pseudoname:"istoriya"},{id:139,ordering:10,name:"Литература",pseudoname:"literatura"},{id:119,ordering:11,name:"Маркетинг",pseudoname:"marketing"},{id:114,ordering:12,name:"Математика",pseudoname:"matematika"},{id:138,ordering:h,name:"Медицина",pseudoname:"medetsina"},{id:118,ordering:14,name:"Менеджмент",pseudoname:"menedzhment"},{id:137,ordering:15,name:"Музыка",pseudoname:"muzyka"},{id:136,ordering:16,name:"МХК",pseudoname:"mhk"},{id:130,ordering:17,name:"Немецкий язык",pseudoname:"nemetskiy-yazyk"},{id:105,ordering:18,name:"ОБЖ",pseudoname:"obzh"},{id:133,ordering:19,name:"Обществознание ",pseudoname:"obshchestvoznanie"},{id:132,ordering:20,name:"Окружающий мир ",pseudoname:"okruzhayushchiy-mir"},{id:131,ordering:21,name:"Педагогика ",pseudoname:"pedagogika"},{id:129,ordering:22,name:"Русский язык",pseudoname:"russkiy-yazyk"},{id:128,ordering:24,name:"Технология",pseudoname:"tehnologiya"},{id:127,ordering:25,name:"Физика",pseudoname:"fizika"},{id:126,ordering:26,name:"Философия",pseudoname:"filosofiya"},{id:125,ordering:27,name:"Химия",pseudoname:"himiya"},{id:124,ordering:29,name:"Экология",pseudoname:"ekologiya"},{id:121,ordering:30,name:"Экономика",pseudoname:"ekonomika"},{id:120,ordering:31,name:"Юриспруденция",pseudoname:"yurisprudentsiya"}]}},state:{},_errors:{},serverRendered:e,config:{public:{SITE_NAME:K,SITE_HOST:"mypreza.com",SITE_LANG:L,API_BASE_URL:"https:\u002F\u002Fmypreza.com\u002Fapi\u002F",pwaManifest:{name:K,short_name:a,description:a,lang:L,start_url:"\u002F?standalone=true",display:"standalone",background_color:j,theme_color:"#000000",icons:[{src:"\u002F_nuxt\u002Ficons\u002F64x64.f2a6e93d.png",type:d,sizes:M,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F64x64.maskable.f2a6e93d.png",type:d,sizes:M,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F120x120.f2a6e93d.png",type:d,sizes:N,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F120x120.maskable.f2a6e93d.png",type:d,sizes:N,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F144x144.f2a6e93d.png",type:d,sizes:O,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F144x144.maskable.f2a6e93d.png",type:d,sizes:O,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F152x152.f2a6e93d.png",type:d,sizes:P,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F152x152.maskable.f2a6e93d.png",type:d,sizes:P,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F192x192.f2a6e93d.png",type:d,sizes:Q,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F192x192.maskable.f2a6e93d.png",type:d,sizes:Q,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F384x384.f2a6e93d.png",type:d,sizes:R,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F384x384.maskable.f2a6e93d.png",type:d,sizes:R,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F512x512.f2a6e93d.png",type:d,sizes:S,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F512x512.maskable.f2a6e93d.png",type:d,sizes:S,purpose:g}]},yandexMetrika:{id:"85004146",metrikaUrl:"https:\u002F\u002Fmc.yandex.ru\u002Fmetrika\u002Ftag.js",accurateTrackBounce:e,childIframe:c,clickmap:c,defer:c,useRuntimeConfig:e,trackHash:c,trackLinks:e,type:b,webvisor:c,triggerEvent:c,consoleLog:e,partytown:c,isDev:c}},app:{baseURL:"\u002F",buildAssetsDir:"\u002F_nuxt\u002F",cdnURL:a}},pinia:{app:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F,token:a}}}}("",0,false,"image\u002Fpng",true,"any","maskable",13,"#d53032","#ffffff","Generics. (Lecture 7.3)","Учебные презентации","Презентации в PowerPoint на разные темы","Презентации, проекты, доклады в PowerPoint на разные темы для учебы","Презентация, на тему, урок, класс, PowerPoint, скачати презентацію, фон, шаблон, доклад, проект.","images\u002Fdata\u002Flogo.png",185,40,720,480,"6LeioWIpAAAAAGqMN4KqMVIkekcMW7fBKHjXCd-a","2503267","[e-mail]","h3a","text","none","h3","category","both",80,800,"\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fes5-shims\u002F0.0.2\u002Fes5-shims.min.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fshare2\u002Fshare.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cdiv class=\"ya-share2\" data-services=\"collections,gplus,vkontakte,facebook,odnoklassniki,gplus,twitter,moimir\" data-counter=\"\"\u003E\u003C\u002Fdiv\u003E","Информатика",144,"\u003Cp\u003EWhich will compile?\u003Cbr\u003E1) List\u003C?\u003E list = new ArrayList\u003CDog\u003E();\u003Cbr\u003E2) List\u003C? extends Animal\u003E aList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E3) List\u003C?\u003E foo = new ArrayList\u003C? extends Animal\u003E();\u003Cbr\u003E4) List\u003C? extends Dog\u003E cList = new ArrayList\u003CInteger\u003E();\u003Cbr\u003E5) List\u003C? super Dog\u003E bList = new ArrayList\u003CAnimal\u003E();\u003Cbr\u003E6) List\u003C? super Animal\u003E dList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E",1,"Mypreza","ru","64x64","120x120","144x144","152x152","192x192","384x384","512x512"))

There IS a huge difference!
class Main {
void check(Holder
obj) {
obj.set(new Dog());
obj.set(new Cat());
}
public static void main(String[] args) {
Holder
obj = new Holder
();
Main main = new Main();
main.check(obj); // Only Holder
goes here!
}
}
Слайд 37
There IS a huge difference!
class Main {
void check(Holder
obj) {
obj.set(new Dog());
// Error
// Compiler isn't sure that it's really Dog Holder
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
integer = new Holder
();
Main main = new Main();
main.check(dog); // OK
main.check(integer); // OK
}
}
Слайд 38
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 39
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 40
Naming Conventions for Generics
E for an element
K for a map key
V for a
map value
N for a number
T for a generic data type
Use S , U , V , and so on for multiple types in the same class.
Слайд 41
Summary
1) Generics let you enforce compile-time type safety.
Holder
h1 = new Holder
();
Holder h2 =
new Holder();
String s = h1.get(); // no cast needed
String s = (String) h2.get(); // cast required
2) Generic type information does not exist at runtime — it is for compile-time safety only.
3) Polymorphic assignment don't apply to the generic type
Holder
h1 = new Holder
(); // Error
4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:
void foo(List
d) {} // can take only
void foo(List
) {} // take a
or
void foo(List
) {} // take a
or
5) When using a wildcard, List
, the collection can be accessed but not modified.
Имя файла: Generics.-(Lecture-7.3).pptx
Количество просмотров: 144
Количество скачиваний: 0
Скачать
- Предыдущая
Internet technologies
Следующая -
Трагедия Гёте Фауст
Похожие презентации
Научно-техническая информация
Презентация к аттестации учителя информатики
Основные компоненты ПК
Арифметические основы организации ЭВМ
Вёрстка и дизайн газетной статьи
Алгоритм действий родителей для прохождения регистрации их детей младше/старше 14 лет во ФГИС Моя школа
Керування правами доступу
Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)
Взаимодействие клиента и сервера
Как с нуля запустить Онлайн-школу
Программа Project Expert
What is cryptocurrency
История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД
WORD-тын графикалык мумкіндіктері
Компьютер как универсальное устройство обработки информации
Линейное программирование
ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области
Социальная память. Функция социальной памяти
Різновиди діаграм та їх форматування
Лекция 2. Файлы (текстовые). Массивы
3D моделирование в программе Tinkercad
Load testing with Visual Studio Enterprise 2015
Информация, ее свойства. Информация и управление
Информационные технологии в ДОУ
Security. The goal
Интернет желісіне жалпы сипаттама
Особенности работы с информацией в различных типах источников. Лекция 3
Презентация к уроку информатики в 5 классе по теме Метод координат
Обратная связь
Email:
Нажмите что бы посмотреть
window.__NUXT__=(function(a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S){return {data:{meta:{result:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F}},item:{result:{id:139284,name:k,category:G,count:42,jpg:"jpg\u002F139284",hits:H,download:b,h1:"Generics. (Lecture 7.3) презентация",meta:{h1:k,title:k,description:"Generics. (Lecture 7.3) презентация на тему, доклад, Информатика",keywords:"Generics. (Lecture 7.3), презентация, доклад, проект, скачать, на тему, PowerPoint, урок, класс, школа, Информатика",download_link:a},text:"Вы можете изучить и скачать доклад-презентацию на тему Презентация на тему Generics. (Lecture 7.3) из раздела Информатика. Презентация на заданную тему содержит 42 слайдов. Для просмотра воспользуйтесь проигрывателем, если материал оказался полезным для Вас - поделитесь им с друзьями с помощью социальных кнопок и добавьте наш сайт презентаций в закладки!",seo_text:"\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E \u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E",file:"Generics.-(Lecture-7.3).pptx",texts:["\u003Cp\u003EGenerics\u003Cbr\u003E","\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E","\u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E","\u003Cp\u003EA class that holds a single object\u003Cbr\u003Eclass Automobile {}\u003Cbr\u003Epublic class Holder1 {\u003Cbr\u003E private Automobile a;\u003Cbr\u003E public Holder1(Automobile a) {\u003Cbr\u003E this.a = a;\u003Cbr\u003E }\u003Cbr\u003E Automobile get() { return a; }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EA class that holds an Object\u003Cbr\u003Epublic class Holder2 { \r\n private Object a; \r\n public Holder2(Object a) { this.a = a; } \r\n\r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder2 h2 = new Holder2(new Automobile()); \r\n Automobile a = (Automobile) h2.get(); \r\n h2.set(\"Not an Automobile\"); \r\n String s = (String) h2.get(); \r\n h2.set(1); \u002F\u002F Autoboxes to Integer \r\n Integer x = (Integer) h2.get(); \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003ESimple generic class\u003Cbr\u003E\r\npublic class Holder3\u003CT\u003E { \u003Cbr\u003E private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder3\u003CAutomobile\u003E h3 =\r\n new Holder3\u003CAutomobile\u003E(new Automobile()); \r\n Automobile a = h3.get(); \u002F\u002F No cast needed \r\n \u002F\u002F h3.set(\"Not an Automobile\"); \u002F\u002F Error \r\n \u002F\u002F h3.set(1); \u002F\u002F Error \r\n } \r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Types and Methods\u003Cbr\u003E\u003Cp\u003EThere can be:\u003Cbr\u003EGeneric classes\u003Cbr\u003EGeneric interfaces\u003Cbr\u003EGeneric methods\u003Cbr\u003EBounded generic types\u003Cbr\u003EGeneric wildcards\u003Cbr\u003E","\u003Cp\u003EThe core idea of Java generics: You tell it what type you want to use, and it takes care of the details.\u003Cbr\u003E","\u003Cp\u003EType erasure\u003Cbr\u003E\u003Cp\u003EJava generics are implemented using type erasure. This means that any specific type information is erased when you compile your code.\u003Cbr\u003E","\u003Cp\u003EHow type erasure works?\u003Cbr\u003E\u003Cp\u003Epublic class Holder3\u003CT\u003E { \r\n private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3\u003CLong\u003E h3 =\u003Cbr\u003E new Holder3\u003CLong\u003E(1L);\u003Cbr\u003ELong n = h3.get();\u003Cbr\u003E\u003Cp\u003Epublic class Holder3 { \r\n private Object a; \r\n\r\n public Holder3(Object a) { this.a = a; } \r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3 h3 = new Holder3(1L);\u003Cbr\u003ELong n = (Long) h3.get();\u003Cbr\u003E","\u003Cp\u003ECompensating for erasure\r\n\r\npublic class Erased\u003CT\u003E {\r\n private final int SIZE = 100;\r\n\r\n public static void f(Object arg) {\r\n if(arg instanceof T) {} \u002F\u002F Error\r\n T var = new T(); \u002F\u002F Error\r\n T[] array = new T[SIZE]; \u002F\u002F Error\r\n T[] array = (T[])new Object[SIZE]; \u002F\u002F Unchecked \t\t\t\t\t\t\twarning\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric class with two types\r\n\r\npublic class TwoTuple\u003CA, B\u003E { \r\n public final A first; \r\n public final B second; \r\n\r\n public TwoTuple(A a, B b) { first = a; second = b; } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \")\"; \r\n } \r\n} \u003Cbr\u003E","\u003Cp\u003EYou cannot use primitives as type parameters!\r\n\r\nTwoTuple\u003CString, Integer\u003E ttsi = new TwoTuple\u003CString, Integer\u003E(\"hi\", 47);\r\n\r\nbut not\r\n\r\nTwoTuple\u003Cdouble, int\u003E ttdi = new TwoTuple\u003Cdouble, int\u003E(47.0, 47);\u003Cbr\u003E","\u003Cp\u003EInheritance with generic classes\r\n\r\npublic class ThreeTuple\u003CA, B, C\u003E extends TwoTuple\u003CA, B\u003E { \r\n public final C third; \r\n\r\n public ThreeTuple(A a, B b, C c) { \r\n super(a, b); \r\n third = c; \r\n } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \", \" +\r\n third +\")\"; \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric interface\u003Cbr\u003E\r\npublic interface Generator\u003CT\u003E { T next(); }\r\n\r\npublic class Fibonacci implements Generator\u003CInteger\u003E {\r\n private int count = 0;\r\n public Integer next() { return fib(count++); }\u003Cbr\u003E \u003Cbr\u003E ...\u003Cbr\u003E\r\n public static void main(String[] args) {\r\n Fibonacci gen = new Fibonacci();\r\n for(int i = 0; i \u003C 18; i++)\r\n System.out.print(gen.next() + \" \");\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Methods\r\n\r\npublic class GenericMethods {\r\n public \u003CT\u003E void f(T x) {\r\n System.out.println(x.getClass().getName());\r\n }\r\n public static void main(String[] args) {\r\n GenericMethods gm = new GenericMethods();\r\n gm.f(\"\");\r\n gm.f(1);\r\n gm.f(1.0);\r\n gm.f('c');\r\n gm.f(new String[] {“H”, “W”});\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EThe Syntax for Invoking a Generic Method\u003Cbr\u003EGenerics have an optional syntax for specifying the type for a generic method. You can place the data type of the generic in angle brackets, \u003C \u003E , after the dot operator and before the method call.\u003Cbr\u003E\r\n gm.\u003CString\u003Ef(“a string object”);\r\n gm.\u003CInteger\u003Ef(1);\r\n gm.\u003CDouble\u003Ef(1.0);\r\n gm.\u003CChar\u003Ef('c');\u003Cbr\u003E gm.\u003CString[]\u003Ef(new String[] {“H”, “W”});\u003Cbr\u003EThe syntax makes the code more readable and also gives you control over the generic type in situations where the type might not be obvious.\u003Cbr\u003E","\u003Cp\u003ELeveraging type argument inference \r\n\r\npublic class Tuple {\r\n public static \u003CA,B\u003E TwoTuple\u003CA,B\u003E tuple(A a, B b) {\r\n return new TwoTuple\u003CA,B\u003E(a, b);\r\n }\r\n public static \u003CA,B,C\u003E ThreeTuple\u003CA,B,C\u003E tuple(A a,B b,C c) {\r\n return new ThreeTuple\u003CA,B,C\u003E(a, b, c);\r\n }\r\n}\r\n...\r\nTwoTuple\u003CString, Integer\u003E ttsi = Tuple.tuple(“hi”, 47);\r\nThreeTuple\u003CString,Integer,Double\u003E ttsid=Tuple.tuple(“hi”,47,47.0);\u003Cbr\u003E","\u003Cp\u003EAnonymous inner classes\r\n\r\npublic interface Generator\u003CT\u003E { T next(); } \r\n\r\nclass Customer { \r\n private Customer() {} \r\n\r\n public static Generator\u003CCustomer\u003E generator() { \r\n return new Generator\u003CCustomer\u003E() { \r\n public Customer next() { return new Customer(); } \r\n }; \r\n } \r\n} \r\n...\r\nCustomer customer1 = Customer.generator().next();\r\nCustomer customer2 = Customer.generator().next();\u003Cbr\u003E","\u003Cp\u003EBounded Generic Types\u003Cbr\u003EBecause erasure removes type information, the only methods you can call for an unbounded generic parameter are those available for Object. Bounds allow you to place constraints on the parameter types. Important effect is that you can call methods that are in your bound types.\u003Cbr\u003Einterface HasColor {\u003Cbr\u003E Color getColor();\u003Cbr\u003E}\u003Cbr\u003Eclass Colored\u003CT extends HasColor\u003E {\r\n T item;\u003Cbr\u003E public Colored(T item) { this.item = item; }\u003Cbr\u003E public T getItem() { return item; }\r\n\u003Cbr\u003E \u002F\u002F The bound allows you to call a method:\r\n public Color color() { return item.getColor(); }\r\n}\u003Cbr\u003E","\u003Cp\u003ECompound bounds\u003Cbr\u003Eclass Dimension { public int x, y, z; } \u003Cbr\u003E\u002F\u002F Multiple bounds: \r\nclass ColoredDimension\u003CT extends Dimension & HasColor\u003E { \r\n T item; \r\n ColoredDimension(T item) { this.item = item; } \r\n T getItem() { return item; } \r\n Color color() { return item.getColor(); } \r\n int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EBounds and Inheritance\u003Cbr\u003E\r\nclass HoldItem\u003CT\u003E {\r\n T item;\r\n HoldItem(T item) { this.item = item; }\r\n T getItem() { return item; }\r\n}\u003Cbr\u003E\r\nclass Colored2\u003CT extends HasColor\u003E extends HoldItem\u003CT\u003E { \r\n \u002F\u002F some code here...\u003Cbr\u003E Color color() { return item.getColor(); } \r\n}\u003Cbr\u003E\r\nclass ColoredDimension2\u003CT extends Dimension & HasColor\u003E\r\n extends Colored2\u003CT\u003E {\r\n \u002F\u002F some code here...\u003Cbr\u003E int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EPolymorphism and Generics\u003Cbr\u003E\r\nclass Holder\u003CT\u003E {\r\n T item;\r\n void set(T item) { this.item = item; }\r\n T get() { return item; }\r\n}\r\nabstract class Parent { }\u003Cbr\u003Eclass Child extends Parent { }\u003Cbr\u003Eclass AnotherChild extends Parent { }\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CChild\u003E h1 = new Holder\u003CChild\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h2 = new Holder\u003CParent\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h3 = new Holder\u003CChild\u003E(); \u002F\u002F Error\u003Cbr\u003E\u002F\u002F because one could do this:\u003Cbr\u003E\u002F\u002F h3.set(new AnotherChild());\u003Cbr\u003E","\u003Cp\u003EWhy Polymorphism doesn’t work\u003Cbr\u003E\u003Cp\u003Eclass Holder\u003CT\u003E {\r\n T[] items;\u003Cbr\u003E int num = 0;\r\n void add(T item) { this.items[num++] = item;}\r\n T[] get() { return items; }\r\n}\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CInteger\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003EHolder\u003CNumber\u003E reg = h;\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003EInteger i3 = h.get()[2]\u003Cbr\u003ESo Double is a Number but Holder\u003CDouble\u003E is not Holder\u003CNumber\u003E \u003Cbr\u003E\u003Cp\u003EClass case exception Double != Integer\u003Cbr\u003E\u003Cp\u003Eh -\u003E {Integer, Integer, Double}\u003Cbr\u003E\u003Cp\u003EIf polymorphism was allowed this would be legal\u003Cbr\u003E\u003Cp\u003EThis is also legal since Double is a Number\u003Cbr\u003E","\u003Cp\u003EBut you can do this:\u003Cbr\u003E\u003Cp\u003EThis is how you can put different object types in parameterized Holder object:\u003Cbr\u003EHolder\u003CNumber\u003E h = new Holder\u003CNumber\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003ENumber i3 = h.get()[2]\u003Cbr\u003E\u003Cp\u003EBoth Integer and Double are the Numbers\u003Cbr\u003E","\u003Cp\u003EMore Example\u003Cbr\u003Eabstract class Animal { public abstract void check(); }\u003Cbr\u003Eclass Dog extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Dog\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass Cat extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Cat\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003CAnimal\u003E animal) {\u003Cbr\u003E animal.get().check();\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F Error\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F Error\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EGeneric Wildcards (?)\u003Cbr\u003E\u003Cp\u003EThe wildcard provides a polymorphic - like behavior for declaring generics.\u003Cbr\u003E\u003C?\u003E , an unbounded wildcard\u003Cbr\u003E\u003C? extends type\u003E , a wildcard with an upper bound\u003Cbr\u003E\u003C? super type\u003E , a wildcard with a lower bound\u003Cbr\u003E","\u003Cp\u003EUnbounded Wildcards\u003Cbr\u003E\u003Cp\u003EThe unbounded wildcard represents any data type, similar to the \u003C T \u003E syntax. \u003Cbr\u003Epublic static void printList(List\u003C?\u003E list) {\u003Cbr\u003E for(Object x : list) {\u003Cbr\u003E System.out.println(x.toString());\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E...\u003Cbr\u003EArrayList\u003CString\u003E keywords = new ArrayList\u003CString\u003E();\u003Cbr\u003Ekyewords.add(“generic”);\u003Cbr\u003EprintList(keywords);\u003Cbr\u003EUse the ? in situations where you do not need a formal parameter type like \u003C T \u003E\u003Cbr\u003E\u003Cp\u003EData type is not required here\u003Cbr\u003E","\u003Cp\u003EBe careful\u003Cbr\u003E\u003Cp\u003EHolder\u003C?\u003E h = new Holder\u003CString\u003E();\u003Cbr\u003Eh.add(new Object()); \u002F\u002F compile time error\u003Cbr\u003Eh.add(new String()); \u002F\u002F compile time error\u003Cbr\u003E\u002F\u002F one exception!\u003Cbr\u003Eh.add(null); \u002F\u002F null is member of every type\u003Cbr\u003E\u003Cbr\u003EWorking with unbounded wildcards we can only read data, not assign!\u003Cbr\u003E\u003Cbr\u003E","\u003Cp\u003EUpper - Bound Wildcards\u003Cbr\u003E\u003Cp\u003EBounded wildcards put some restrictions on unknown type:\u003Cbr\u003Epublic static void printList(List\u003C? extends Number\u003E list){\u003Cbr\u003E for(Number x : list) {\u003Cbr\u003E System.out.println(x.doubleValue());\u003Cbr\u003E }\u003Cbr\u003E list.add(new Integer(3)); \u002F\u002F compile error\u003Cbr\u003E}\u003Cbr\u003E\u003Cp\u003ENow we know that object is instance of Number\u003Cbr\u003E\u003Cp\u003EBut we still don’t know exact type, so can’t modify list\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? extends Animal\u003E animal) {\u003Cbr\u003E animal.get().check(); \u002F\u002F OK\u003Cbr\u003E animal.set(new Cat()); \u002F\u002F Error: we don’t know exact parameter type of animal\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003ELower Bounded Wildcards\u003Cbr\u003E\u003Cp\u003Ea lower bounded wildcard restricts the unknown type to be a specific type or a super type of that type\u003Cbr\u003EHolder\u003C? super Integer\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(new Integer(1));\u003Cbr\u003EInteger i1 = h.get(); \u002F\u002F compilation error\u003Cbr\u003E\t\t\t\u002F\u002F get returns Object\u003Cbr\u003EInteger i2 = (Integer)h.get(); \u002F\u002F OK\u003Cbr\u003ELower bounded wildcards allow to modify but not read!!\u003Cbr\u003E","\u003Cp\u003EExample\u003Cbr\u003E\u003Cp\u003Epublic static void addNumbers(List\u003C? super Integer\u003E list) {\u003Cbr\u003E for (int i = 1; i \u003C= 10; i++) {\u003Cbr\u003E list.add(i);\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003EList\u003CInteger\u003E i = new ArrayList\u003CInteger\u003E();\u003Cbr\u003EList\u003CNumber\u003E n = new ArrayList\u003CNumber\u003E();\u003Cbr\u003EList\u003CObject\u003E o = new ArrayList\u003CObject\u003E();\u003Cbr\u003E\t\t\u003Cbr\u003EaddNumbers(i);\u003Cbr\u003EaddNumbers(n);\u003Cbr\u003EaddNumbers(o);\u003Cbr\u003EThis works fine\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? super Dog\u003E dog) {\u003Cbr\u003E animal.get().check(); \u002F\u002F Error!\u003Cbr\u003E \u002F\u002F get() returns Object ref\u003Cbr\u003E animal.set(new Dog()); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CAnimal\u003E animal = new Holder\u003CAnimal\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat= new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(animal); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002FError: Cat isn’t super of Dog\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EWhat's the difference?\u003Cbr\u003Evoid check(Holder\u003C?\u003E holder) { }\u003Cbr\u003Evoid check(Holder\u003CObject\u003E holder) { }\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003CObject\u003E obj) {\u003Cbr\u003E obj.set(new Dog());\u003Cbr\u003E obj.set(new Cat());\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CObject\u003E obj = new Holder\u003CObject\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(obj); \u002F\u002F Only Holder\u003CObject\u003E goes here!\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003C?\u003E obj) {\u003Cbr\u003E obj.set(new Dog()); \u002F\u002F Error\u003Cbr\u003E \u002F\u002F Compiler isn't sure that it's really Dog Holder\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CInteger\u003E integer = new Holder\u003CInteger\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(dog); \u002F\u002F OK\u003Cbr\u003E main.check(integer); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E",I,I,"\u003Cp\u003ENaming Conventions for Generics\u003Cbr\u003E\u003Cp\u003EE for an element\u003Cbr\u003EK for a map key\u003Cbr\u003EV for a map value\u003Cbr\u003EN for a number\u003Cbr\u003ET for a generic data type\u003Cbr\u003EUse S , U , V , and so on for multiple types in the same class.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E1) Generics let you enforce compile-time type safety.\u003Cbr\u003EHolder\u003CString\u003E h1 = new Holder\u003CString\u003E();\u003Cbr\u003EHolder h2 = new Holder();\u003Cbr\u003EString s = h1.get(); \u002F\u002F no cast needed\u003Cbr\u003EString s = (String) h2.get(); \u002F\u002F cast required\u003Cbr\u003E2) Generic type information does not exist at runtime — it is for compile-time safety only.\u003Cbr\u003E3) Polymorphic assignment don't apply to the generic type\u003Cbr\u003EHolder\u003CAnimal\u003E h1 = new Holder\u003CDog\u003E(); \u002F\u002F Error\u003Cbr\u003E4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:\u003Cbr\u003Evoid foo(List\u003CDog\u003E d) {} \u002F\u002F can take only \u003CDog\u003E\u003Cbr\u003Evoid foo(List\u003C? extends Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CCollie\u003E\u003Cbr\u003Evoid foo(List\u003C? super Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CAnimal\u003E\u003Cbr\u003E5) When using a wildcard, List\u003C? extends Dog\u003E, the collection can be accessed but not modified.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E6) The generics type identifier can be used in class, method, and variable declarations:\u003Cbr\u003E class Foo\u003Ct\u003E { } \u002F\u002F a class\u003Cbr\u003E T anInstance; \u002F\u002F an instance variable\u003Cbr\u003E Foo(T aRef) {} \u002F\u002F a constructor argument\u003Cbr\u003E void bar(T aRef) {} \u002F\u002F a method argument\u003Cbr\u003E T baz() {} \u002F\u002F a return type\u003Cbr\u003E7) You can use more than one parameterized type in a declaration:\u003Cbr\u003E public class UseTwo\u003CT, X\u003E { }\u003Cbr\u003E8) You can declare a generic method using a type not defined in the class:\u003Cbr\u003E public \u003CT\u003E T returnMe(T t) { return t; }\u003Cbr\u003EReading in Russian\u003Cbr\u003Ehttp:\u002F\u002Fwww.rsdn.ru\u002Farticle\u002Fjava\u002Fgenericsinjava.xml\u003Cbr\u003E"],href:"\u002Finformatika\u002Fgenerics-lecture-73",href_category:"\u002Finformatika",date:1628090801,related:[{id:404222,name:"Научно-техническая информация",href:"\u002Finformatika\u002Fnauchno-tehnicheskaya-informatsiya-1",jpg:"jpg\u002F404222"},{id:478755,name:"Презентация к аттестации учителя информатики",href:"\u002Finformatika\u002Fprezentatsiya-k-attestatsii-uchitelya-informatiki",jpg:"jpg\u002F478755"},{id:4499,name:"Основные компоненты ПК",href:"\u002Finformatika\u002Fosnovnye-komponenty-pk",jpg:"jpg\u002F4499"},{id:184558,name:"Арифметические основы организации ЭВМ",href:"\u002Finformatika\u002Farifmeticheskie-osnovy-organizatsii-evm",jpg:"jpg\u002F184558"},{id:373746,name:"Вёрстка и дизайн газетной статьи",href:"\u002Finformatika\u002Fvyorstka-i-dizayn-gazetnoy-stati",jpg:"jpg\u002F373746"},{id:577279,name:"Алгоритм действий родителей для прохождения регистрации их детей младше\u002Fстарше 14 лет во ФГИС Моя школа",href:"\u002Finformatika\u002Falgoritm-deystviy-roditeley-dlya-prohozhdeniya-registratsii",jpg:"jpg\u002F577279"},{id:12068,name:"Керування правами доступу",href:"\u002Finformatika\u002Fkeruvannya-pravami-dostupu",jpg:"jpg\u002F12068"},{id:403270,name:"Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)",href:"\u002Finformatika\u002Fponyatie-algoritma-svoystva-vidy-tipy-formy",jpg:"jpg\u002F403270"},{id:234266,name:"Взаимодействие клиента и сервера",href:"\u002Finformatika\u002Fvzaimodeystvie-klienta-i-servera",jpg:"jpg\u002F234266"},{id:266792,name:"Как с нуля запустить Онлайн-школу",href:"\u002Finformatika\u002Fkak-s-nulya-zapustit-onlayn-shkolu",jpg:"jpg\u002F266792"},{id:104353,name:"Программа Project Expert",href:"\u002Finformatika\u002Fprogramma-project-expert",jpg:"jpg\u002F104353"},{id:3725,name:"What is cryptocurrency",href:"\u002Finformatika\u002Fwhat-is-cryptocurrency",jpg:"jpg\u002F3725"},{id:1966,name:"История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД",href:"\u002Finformatika\u002Fistoriya-razvitiya-i-pokoleniya-subd-klassifikatsiya",jpg:"jpg\u002F1966"},{id:253599,name:"WORD-тын графикалык мумкіндіктері",href:"\u002Finformatika\u002Fword-tyn-grafikalyk-mumkndkter",jpg:"jpg\u002F253599"},{id:215026,name:"Компьютер как универсальное устройство обработки информации",href:"\u002Finformatika\u002Fkompyuter-kak-universalnoe-ustroystvo-obrabotki-informatsii",jpg:"jpg\u002F215026"},{id:200593,name:"Линейное программирование",href:"\u002Finformatika\u002Flineynoe-programmirovanie-2",jpg:"jpg\u002F200593"},{id:429765,name:"ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области",href:"\u002Finformatika\u002Fou-novoseletskaya-shkola-navigator-dopolnitelnogo-obrazovaniya",jpg:"jpg\u002F429765"},{id:383037,name:"Социальная память. Функция социальной памяти",href:"\u002Finformatika\u002Fsotsialnaya-pamyat-funktsiya-sotsialnoy-pamyati",jpg:"jpg\u002F383037"},{id:160929,name:"Різновиди діаграм та їх форматування",href:"\u002Finformatika\u002Frznovidi-dagram-ta-h-formatuvannya",jpg:"jpg\u002F160929"},{id:266355,name:"Лекция 2. Файлы (текстовые). Массивы",href:"\u002Finformatika\u002Flektsiya-2-fayly-tekstovye-massivy",jpg:"jpg\u002F266355"},{id:610347,name:"3D моделирование в программе Tinkercad",href:"\u002Finformatika\u002F3d-modelirovanie-v-programme-tinkercad",jpg:"jpg\u002F610347"},{id:393791,name:"Load testing with Visual Studio Enterprise 2015",href:"\u002Finformatika\u002Fload-testing-with-visual-studio-enterprise",jpg:"jpg\u002F393791"},{id:114799,name:"Информация, ее свойства. Информация и управление",href:"\u002Finformatika\u002Finformatsiya-ee-svoystva-informatsiya-i-upravlenie",jpg:"jpg\u002F114799"},{id:435506,name:"Информационные технологии в ДОУ",href:"\u002Finformatika\u002Finformatsionnye-tehnologii-v-dou",jpg:"jpg\u002F435506"},{id:439332,name:"Security. The goal",href:"\u002Finformatika\u002Fsecurity-the-goal",jpg:"jpg\u002F439332"},{id:15166,name:"Интернет желісіне жалпы сипаттама",href:"\u002Finformatika\u002Finternet-zhelsne-zhalpy-sipattama",jpg:"jpg\u002F15166"},{id:326320,name:"Особенности работы с информацией в различных типах источников. Лекция 3",href:"\u002Finformatika\u002Fosobennosti-raboty-s-informatsiey-v-razlichnyh",jpg:"jpg\u002F326320"},{id:503963,name:"Презентация к уроку информатики в 5 классе по теме Метод координат",href:"\u002Finformatika\u002Fprezentatsiya-k-uroku-informatiki-v-5-6",jpg:"jpg\u002F503963"}],navigation:{next:"\u002Fliteratura\u002Ftragediya-gyote-faust-2",next_name:"Трагедия Гёте Фауст",prev:"\u002Finformatika\u002Finternet-technologies-2",prev_name:"Internet technologies"}}},categories:{result:[{id:J,ordering:b,name:"Без категории",pseudoname:"uncategorized"},{id:H,ordering:b,name:"Бизнес",pseudoname:"biznes"},{id:146,ordering:b,name:"Образование",pseudoname:"obrazovanie"},{id:149,ordering:b,name:"Финансы",pseudoname:"finansy"},{id:150,ordering:b,name:"Государство",pseudoname:"gosudarstvo"},{id:152,ordering:b,name:"Спорт",pseudoname:"sport"},{id:154,ordering:b,name:"Армия",pseudoname:"armiya"},{id:156,ordering:b,name:"Культурология",pseudoname:"kulturologiya"},{id:157,ordering:b,name:"Еда и кулинария",pseudoname:"eda-i-kulinariya"},{id:158,ordering:b,name:"Лингвистика",pseudoname:"lingvistika"},{id:163,ordering:b,name:"Черчение",pseudoname:"cherchenie"},{id:164,ordering:b,name:"Физкультура",pseudoname:"fizkultura"},{id:165,ordering:b,name:"ИЗО",pseudoname:"izo"},{id:166,ordering:b,name:"Психология",pseudoname:"psihologiya"},{id:116,ordering:J,name:"Английский язык",pseudoname:"angliyskiy-yazyk"},{id:108,ordering:2,name:"Астрономия",pseudoname:"astronomiya"},{id:104,ordering:3,name:"Алгебра",pseudoname:"algebra"},{id:106,ordering:4,name:"Биология",pseudoname:"biologiya"},{id:142,ordering:5,name:"География",pseudoname:"geografiya"},{id:141,ordering:6,name:"Геометрия",pseudoname:"geometria"},{id:123,ordering:7,name:"Детские презентации",pseudoname:"detskie-prezentatsii"},{id:107,ordering:8,name:G,pseudoname:"informatika"},{id:109,ordering:9,name:"История",pseudoname:"istoriya"},{id:139,ordering:10,name:"Литература",pseudoname:"literatura"},{id:119,ordering:11,name:"Маркетинг",pseudoname:"marketing"},{id:114,ordering:12,name:"Математика",pseudoname:"matematika"},{id:138,ordering:h,name:"Медицина",pseudoname:"medetsina"},{id:118,ordering:14,name:"Менеджмент",pseudoname:"menedzhment"},{id:137,ordering:15,name:"Музыка",pseudoname:"muzyka"},{id:136,ordering:16,name:"МХК",pseudoname:"mhk"},{id:130,ordering:17,name:"Немецкий язык",pseudoname:"nemetskiy-yazyk"},{id:105,ordering:18,name:"ОБЖ",pseudoname:"obzh"},{id:133,ordering:19,name:"Обществознание ",pseudoname:"obshchestvoznanie"},{id:132,ordering:20,name:"Окружающий мир ",pseudoname:"okruzhayushchiy-mir"},{id:131,ordering:21,name:"Педагогика ",pseudoname:"pedagogika"},{id:129,ordering:22,name:"Русский язык",pseudoname:"russkiy-yazyk"},{id:128,ordering:24,name:"Технология",pseudoname:"tehnologiya"},{id:127,ordering:25,name:"Физика",pseudoname:"fizika"},{id:126,ordering:26,name:"Философия",pseudoname:"filosofiya"},{id:125,ordering:27,name:"Химия",pseudoname:"himiya"},{id:124,ordering:29,name:"Экология",pseudoname:"ekologiya"},{id:121,ordering:30,name:"Экономика",pseudoname:"ekonomika"},{id:120,ordering:31,name:"Юриспруденция",pseudoname:"yurisprudentsiya"}]}},state:{},_errors:{},serverRendered:e,config:{public:{SITE_NAME:K,SITE_HOST:"mypreza.com",SITE_LANG:L,API_BASE_URL:"https:\u002F\u002Fmypreza.com\u002Fapi\u002F",pwaManifest:{name:K,short_name:a,description:a,lang:L,start_url:"\u002F?standalone=true",display:"standalone",background_color:j,theme_color:"#000000",icons:[{src:"\u002F_nuxt\u002Ficons\u002F64x64.f2a6e93d.png",type:d,sizes:M,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F64x64.maskable.f2a6e93d.png",type:d,sizes:M,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F120x120.f2a6e93d.png",type:d,sizes:N,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F120x120.maskable.f2a6e93d.png",type:d,sizes:N,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F144x144.f2a6e93d.png",type:d,sizes:O,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F144x144.maskable.f2a6e93d.png",type:d,sizes:O,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F152x152.f2a6e93d.png",type:d,sizes:P,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F152x152.maskable.f2a6e93d.png",type:d,sizes:P,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F192x192.f2a6e93d.png",type:d,sizes:Q,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F192x192.maskable.f2a6e93d.png",type:d,sizes:Q,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F384x384.f2a6e93d.png",type:d,sizes:R,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F384x384.maskable.f2a6e93d.png",type:d,sizes:R,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F512x512.f2a6e93d.png",type:d,sizes:S,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F512x512.maskable.f2a6e93d.png",type:d,sizes:S,purpose:g}]},yandexMetrika:{id:"85004146",metrikaUrl:"https:\u002F\u002Fmc.yandex.ru\u002Fmetrika\u002Ftag.js",accurateTrackBounce:e,childIframe:c,clickmap:c,defer:c,useRuntimeConfig:e,trackHash:c,trackLinks:e,type:b,webvisor:c,triggerEvent:c,consoleLog:e,partytown:c,isDev:c}},app:{baseURL:"\u002F",buildAssetsDir:"\u002F_nuxt\u002F",cdnURL:a}},pinia:{app:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F,token:a}}}}("",0,false,"image\u002Fpng",true,"any","maskable",13,"#d53032","#ffffff","Generics. (Lecture 7.3)","Учебные презентации","Презентации в PowerPoint на разные темы","Презентации, проекты, доклады в PowerPoint на разные темы для учебы","Презентация, на тему, урок, класс, PowerPoint, скачати презентацію, фон, шаблон, доклад, проект.","images\u002Fdata\u002Flogo.png",185,40,720,480,"6LeioWIpAAAAAGqMN4KqMVIkekcMW7fBKHjXCd-a","2503267","[e-mail]","h3a","text","none","h3","category","both",80,800,"\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fes5-shims\u002F0.0.2\u002Fes5-shims.min.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fshare2\u002Fshare.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cdiv class=\"ya-share2\" data-services=\"collections,gplus,vkontakte,facebook,odnoklassniki,gplus,twitter,moimir\" data-counter=\"\"\u003E\u003C\u002Fdiv\u003E","Информатика",144,"\u003Cp\u003EWhich will compile?\u003Cbr\u003E1) List\u003C?\u003E list = new ArrayList\u003CDog\u003E();\u003Cbr\u003E2) List\u003C? extends Animal\u003E aList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E3) List\u003C?\u003E foo = new ArrayList\u003C? extends Animal\u003E();\u003Cbr\u003E4) List\u003C? extends Dog\u003E cList = new ArrayList\u003CInteger\u003E();\u003Cbr\u003E5) List\u003C? super Dog\u003E bList = new ArrayList\u003CAnimal\u003E();\u003Cbr\u003E6) List\u003C? super Animal\u003E dList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E",1,"Mypreza","ru","64x64","120x120","144x144","152x152","192x192","384x384","512x512")) obj.set(new Cat());
}
public static void main(String[] args) {
Holder
obj = new Holder
();
Main main = new Main();
main.check(obj); // Only Holder
goes here!
}
}
Слайд 37
There IS a huge difference!
class Main {
void check(Holder
obj) {
obj.set(new Dog());
// Error
// Compiler isn't sure that it's really Dog Holder
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
integer = new Holder
();
Main main = new Main();
main.check(dog); // OK
main.check(integer); // OK
}
}
Слайд 38
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 39
Which will compile?
1) List
list = new ArrayList
();
2) List
aList =
new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();
Слайд 40
Naming Conventions for Generics
E for an element
K for a map key
V for a
map value
N for a number
T for a generic data type
Use S , U , V , and so on for multiple types in the same class.
Слайд 41
Summary
1) Generics let you enforce compile-time type safety.
Holder
h1 = new Holder
();
Holder h2 =
new Holder();
String s = h1.get(); // no cast needed
String s = (String) h2.get(); // cast required
2) Generic type information does not exist at runtime — it is for compile-time safety only.
3) Polymorphic assignment don't apply to the generic type
Holder
h1 = new Holder
(); // Error
4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:
void foo(List
d) {} // can take only
void foo(List
) {} // take a
or
void foo(List
) {} // take a
or
5) When using a wildcard, List
, the collection can be accessed but not modified.
Имя файла: Generics.-(Lecture-7.3).pptx
Количество просмотров: 144
Количество скачиваний: 0
Скачать
- Предыдущая
Internet technologies
Следующая -
Трагедия Гёте Фауст
Похожие презентации
Научно-техническая информация
Презентация к аттестации учителя информатики
Основные компоненты ПК
Арифметические основы организации ЭВМ
Вёрстка и дизайн газетной статьи
Алгоритм действий родителей для прохождения регистрации их детей младше/старше 14 лет во ФГИС Моя школа
Керування правами доступу
Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)
Взаимодействие клиента и сервера
Как с нуля запустить Онлайн-школу
Программа Project Expert
What is cryptocurrency
История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД
WORD-тын графикалык мумкіндіктері
Компьютер как универсальное устройство обработки информации
Линейное программирование
ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области
Социальная память. Функция социальной памяти
Різновиди діаграм та їх форматування
Лекция 2. Файлы (текстовые). Массивы
3D моделирование в программе Tinkercad
Load testing with Visual Studio Enterprise 2015
Информация, ее свойства. Информация и управление
Информационные технологии в ДОУ
Security. The goal
Интернет желісіне жалпы сипаттама
Особенности работы с информацией в различных типах источников. Лекция 3
Презентация к уроку информатики в 5 классе по теме Метод координат
Обратная связь
Email:
Нажмите что бы посмотреть
window.__NUXT__=(function(a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S){return {data:{meta:{result:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F}},item:{result:{id:139284,name:k,category:G,count:42,jpg:"jpg\u002F139284",hits:H,download:b,h1:"Generics. (Lecture 7.3) презентация",meta:{h1:k,title:k,description:"Generics. (Lecture 7.3) презентация на тему, доклад, Информатика",keywords:"Generics. (Lecture 7.3), презентация, доклад, проект, скачать, на тему, PowerPoint, урок, класс, школа, Информатика",download_link:a},text:"Вы можете изучить и скачать доклад-презентацию на тему Презентация на тему Generics. (Lecture 7.3) из раздела Информатика. Презентация на заданную тему содержит 42 слайдов. Для просмотра воспользуйтесь проигрывателем, если материал оказался полезным для Вас - поделитесь им с друзьями с помощью социальных кнопок и добавьте наш сайт презентаций в закладки!",seo_text:"\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E \u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E",file:"Generics.-(Lecture-7.3).pptx",texts:["\u003Cp\u003EGenerics\u003Cbr\u003E","\u003Cp\u003EWhat if you could say that your code works with \"some unspecified type,\" rather than a specific interface or class?\u003Cbr\u003E","\u003Cp\u003EGenerics implement the concept of parameterized types, which allow multiple types. \u003Cbr\u003E","\u003Cp\u003EA class that holds a single object\u003Cbr\u003Eclass Automobile {}\u003Cbr\u003Epublic class Holder1 {\u003Cbr\u003E private Automobile a;\u003Cbr\u003E public Holder1(Automobile a) {\u003Cbr\u003E this.a = a;\u003Cbr\u003E }\u003Cbr\u003E Automobile get() { return a; }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EA class that holds an Object\u003Cbr\u003Epublic class Holder2 { \r\n private Object a; \r\n public Holder2(Object a) { this.a = a; } \r\n\r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder2 h2 = new Holder2(new Automobile()); \r\n Automobile a = (Automobile) h2.get(); \r\n h2.set(\"Not an Automobile\"); \r\n String s = (String) h2.get(); \r\n h2.set(1); \u002F\u002F Autoboxes to Integer \r\n Integer x = (Integer) h2.get(); \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003ESimple generic class\u003Cbr\u003E\r\npublic class Holder3\u003CT\u003E { \u003Cbr\u003E private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n\r\n public static void main(String[] args) { \r\n Holder3\u003CAutomobile\u003E h3 =\r\n new Holder3\u003CAutomobile\u003E(new Automobile()); \r\n Automobile a = h3.get(); \u002F\u002F No cast needed \r\n \u002F\u002F h3.set(\"Not an Automobile\"); \u002F\u002F Error \r\n \u002F\u002F h3.set(1); \u002F\u002F Error \r\n } \r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Types and Methods\u003Cbr\u003E\u003Cp\u003EThere can be:\u003Cbr\u003EGeneric classes\u003Cbr\u003EGeneric interfaces\u003Cbr\u003EGeneric methods\u003Cbr\u003EBounded generic types\u003Cbr\u003EGeneric wildcards\u003Cbr\u003E","\u003Cp\u003EThe core idea of Java generics: You tell it what type you want to use, and it takes care of the details.\u003Cbr\u003E","\u003Cp\u003EType erasure\u003Cbr\u003E\u003Cp\u003EJava generics are implemented using type erasure. This means that any specific type information is erased when you compile your code.\u003Cbr\u003E","\u003Cp\u003EHow type erasure works?\u003Cbr\u003E\u003Cp\u003Epublic class Holder3\u003CT\u003E { \r\n private T a; \r\n\r\n public Holder3(T a) { this.a = a; } \r\n public void set(T a) { this.a = a; } \r\n public T get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3\u003CLong\u003E h3 =\u003Cbr\u003E new Holder3\u003CLong\u003E(1L);\u003Cbr\u003ELong n = h3.get();\u003Cbr\u003E\u003Cp\u003Epublic class Holder3 { \r\n private Object a; \r\n\r\n public Holder3(Object a) { this.a = a; } \r\n public void set(Object a) { this.a = a; } \r\n public Object get() { return a; } \r\n}\u003Cbr\u003E…\u003Cbr\u003EHolder3 h3 = new Holder3(1L);\u003Cbr\u003ELong n = (Long) h3.get();\u003Cbr\u003E","\u003Cp\u003ECompensating for erasure\r\n\r\npublic class Erased\u003CT\u003E {\r\n private final int SIZE = 100;\r\n\r\n public static void f(Object arg) {\r\n if(arg instanceof T) {} \u002F\u002F Error\r\n T var = new T(); \u002F\u002F Error\r\n T[] array = new T[SIZE]; \u002F\u002F Error\r\n T[] array = (T[])new Object[SIZE]; \u002F\u002F Unchecked \t\t\t\t\t\t\twarning\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric class with two types\r\n\r\npublic class TwoTuple\u003CA, B\u003E { \r\n public final A first; \r\n public final B second; \r\n\r\n public TwoTuple(A a, B b) { first = a; second = b; } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \")\"; \r\n } \r\n} \u003Cbr\u003E","\u003Cp\u003EYou cannot use primitives as type parameters!\r\n\r\nTwoTuple\u003CString, Integer\u003E ttsi = new TwoTuple\u003CString, Integer\u003E(\"hi\", 47);\r\n\r\nbut not\r\n\r\nTwoTuple\u003Cdouble, int\u003E ttdi = new TwoTuple\u003Cdouble, int\u003E(47.0, 47);\u003Cbr\u003E","\u003Cp\u003EInheritance with generic classes\r\n\r\npublic class ThreeTuple\u003CA, B, C\u003E extends TwoTuple\u003CA, B\u003E { \r\n public final C third; \r\n\r\n public ThreeTuple(A a, B b, C c) { \r\n super(a, b); \r\n third = c; \r\n } \r\n\r\n public String toString() { \r\n return \"(\" + first + \", \" + second + \", \" +\r\n third +\")\"; \r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric interface\u003Cbr\u003E\r\npublic interface Generator\u003CT\u003E { T next(); }\r\n\r\npublic class Fibonacci implements Generator\u003CInteger\u003E {\r\n private int count = 0;\r\n public Integer next() { return fib(count++); }\u003Cbr\u003E \u003Cbr\u003E ...\u003Cbr\u003E\r\n public static void main(String[] args) {\r\n Fibonacci gen = new Fibonacci();\r\n for(int i = 0; i \u003C 18; i++)\r\n System.out.print(gen.next() + \" \");\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EGeneric Methods\r\n\r\npublic class GenericMethods {\r\n public \u003CT\u003E void f(T x) {\r\n System.out.println(x.getClass().getName());\r\n }\r\n public static void main(String[] args) {\r\n GenericMethods gm = new GenericMethods();\r\n gm.f(\"\");\r\n gm.f(1);\r\n gm.f(1.0);\r\n gm.f('c');\r\n gm.f(new String[] {“H”, “W”});\r\n }\r\n}\u003Cbr\u003E","\u003Cp\u003EThe Syntax for Invoking a Generic Method\u003Cbr\u003EGenerics have an optional syntax for specifying the type for a generic method. You can place the data type of the generic in angle brackets, \u003C \u003E , after the dot operator and before the method call.\u003Cbr\u003E\r\n gm.\u003CString\u003Ef(“a string object”);\r\n gm.\u003CInteger\u003Ef(1);\r\n gm.\u003CDouble\u003Ef(1.0);\r\n gm.\u003CChar\u003Ef('c');\u003Cbr\u003E gm.\u003CString[]\u003Ef(new String[] {“H”, “W”});\u003Cbr\u003EThe syntax makes the code more readable and also gives you control over the generic type in situations where the type might not be obvious.\u003Cbr\u003E","\u003Cp\u003ELeveraging type argument inference \r\n\r\npublic class Tuple {\r\n public static \u003CA,B\u003E TwoTuple\u003CA,B\u003E tuple(A a, B b) {\r\n return new TwoTuple\u003CA,B\u003E(a, b);\r\n }\r\n public static \u003CA,B,C\u003E ThreeTuple\u003CA,B,C\u003E tuple(A a,B b,C c) {\r\n return new ThreeTuple\u003CA,B,C\u003E(a, b, c);\r\n }\r\n}\r\n...\r\nTwoTuple\u003CString, Integer\u003E ttsi = Tuple.tuple(“hi”, 47);\r\nThreeTuple\u003CString,Integer,Double\u003E ttsid=Tuple.tuple(“hi”,47,47.0);\u003Cbr\u003E","\u003Cp\u003EAnonymous inner classes\r\n\r\npublic interface Generator\u003CT\u003E { T next(); } \r\n\r\nclass Customer { \r\n private Customer() {} \r\n\r\n public static Generator\u003CCustomer\u003E generator() { \r\n return new Generator\u003CCustomer\u003E() { \r\n public Customer next() { return new Customer(); } \r\n }; \r\n } \r\n} \r\n...\r\nCustomer customer1 = Customer.generator().next();\r\nCustomer customer2 = Customer.generator().next();\u003Cbr\u003E","\u003Cp\u003EBounded Generic Types\u003Cbr\u003EBecause erasure removes type information, the only methods you can call for an unbounded generic parameter are those available for Object. Bounds allow you to place constraints on the parameter types. Important effect is that you can call methods that are in your bound types.\u003Cbr\u003Einterface HasColor {\u003Cbr\u003E Color getColor();\u003Cbr\u003E}\u003Cbr\u003Eclass Colored\u003CT extends HasColor\u003E {\r\n T item;\u003Cbr\u003E public Colored(T item) { this.item = item; }\u003Cbr\u003E public T getItem() { return item; }\r\n\u003Cbr\u003E \u002F\u002F The bound allows you to call a method:\r\n public Color color() { return item.getColor(); }\r\n}\u003Cbr\u003E","\u003Cp\u003ECompound bounds\u003Cbr\u003Eclass Dimension { public int x, y, z; } \u003Cbr\u003E\u002F\u002F Multiple bounds: \r\nclass ColoredDimension\u003CT extends Dimension & HasColor\u003E { \r\n T item; \r\n ColoredDimension(T item) { this.item = item; } \r\n T getItem() { return item; } \r\n Color color() { return item.getColor(); } \r\n int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EBounds and Inheritance\u003Cbr\u003E\r\nclass HoldItem\u003CT\u003E {\r\n T item;\r\n HoldItem(T item) { this.item = item; }\r\n T getItem() { return item; }\r\n}\u003Cbr\u003E\r\nclass Colored2\u003CT extends HasColor\u003E extends HoldItem\u003CT\u003E { \r\n \u002F\u002F some code here...\u003Cbr\u003E Color color() { return item.getColor(); } \r\n}\u003Cbr\u003E\r\nclass ColoredDimension2\u003CT extends Dimension & HasColor\u003E\r\n extends Colored2\u003CT\u003E {\r\n \u002F\u002F some code here...\u003Cbr\u003E int getX() { return item.x; } \r\n int getY() { return item.y; } \r\n int getZ() { return item.z; } \r\n}\u003Cbr\u003E","\u003Cp\u003EPolymorphism and Generics\u003Cbr\u003E\r\nclass Holder\u003CT\u003E {\r\n T item;\r\n void set(T item) { this.item = item; }\r\n T get() { return item; }\r\n}\r\nabstract class Parent { }\u003Cbr\u003Eclass Child extends Parent { }\u003Cbr\u003Eclass AnotherChild extends Parent { }\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CChild\u003E h1 = new Holder\u003CChild\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h2 = new Holder\u003CParent\u003E(); \u002F\u002F OK\u003Cbr\u003EHolder\u003CParent\u003E h3 = new Holder\u003CChild\u003E(); \u002F\u002F Error\u003Cbr\u003E\u002F\u002F because one could do this:\u003Cbr\u003E\u002F\u002F h3.set(new AnotherChild());\u003Cbr\u003E","\u003Cp\u003EWhy Polymorphism doesn’t work\u003Cbr\u003E\u003Cp\u003Eclass Holder\u003CT\u003E {\r\n T[] items;\u003Cbr\u003E int num = 0;\r\n void add(T item) { this.items[num++] = item;}\r\n T[] get() { return items; }\r\n}\u003Cbr\u003E...\u003Cbr\u003EHolder\u003CInteger\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003EHolder\u003CNumber\u003E reg = h;\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003EInteger i3 = h.get()[2]\u003Cbr\u003ESo Double is a Number but Holder\u003CDouble\u003E is not Holder\u003CNumber\u003E \u003Cbr\u003E\u003Cp\u003EClass case exception Double != Integer\u003Cbr\u003E\u003Cp\u003Eh -\u003E {Integer, Integer, Double}\u003Cbr\u003E\u003Cp\u003EIf polymorphism was allowed this would be legal\u003Cbr\u003E\u003Cp\u003EThis is also legal since Double is a Number\u003Cbr\u003E","\u003Cp\u003EBut you can do this:\u003Cbr\u003E\u003Cp\u003EThis is how you can put different object types in parameterized Holder object:\u003Cbr\u003EHolder\u003CNumber\u003E h = new Holder\u003CNumber\u003E();\u003Cbr\u003Eh.add(1);\u003Cbr\u003Eh.add(2);\u003Cbr\u003Eh.add(new Double(1.25));\u003Cbr\u003ENumber i3 = h.get()[2]\u003Cbr\u003E\u003Cp\u003EBoth Integer and Double are the Numbers\u003Cbr\u003E","\u003Cp\u003EMore Example\u003Cbr\u003Eabstract class Animal { public abstract void check(); }\u003Cbr\u003Eclass Dog extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Dog\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass Cat extends Animal {\u003Cbr\u003E public void check() { S.o.p(\"Cat\"); }\u003Cbr\u003E}\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003CAnimal\u003E animal) {\u003Cbr\u003E animal.get().check();\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F Error\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F Error\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EGeneric Wildcards (?)\u003Cbr\u003E\u003Cp\u003EThe wildcard provides a polymorphic - like behavior for declaring generics.\u003Cbr\u003E\u003C?\u003E , an unbounded wildcard\u003Cbr\u003E\u003C? extends type\u003E , a wildcard with an upper bound\u003Cbr\u003E\u003C? super type\u003E , a wildcard with a lower bound\u003Cbr\u003E","\u003Cp\u003EUnbounded Wildcards\u003Cbr\u003E\u003Cp\u003EThe unbounded wildcard represents any data type, similar to the \u003C T \u003E syntax. \u003Cbr\u003Epublic static void printList(List\u003C?\u003E list) {\u003Cbr\u003E for(Object x : list) {\u003Cbr\u003E System.out.println(x.toString());\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E...\u003Cbr\u003EArrayList\u003CString\u003E keywords = new ArrayList\u003CString\u003E();\u003Cbr\u003Ekyewords.add(“generic”);\u003Cbr\u003EprintList(keywords);\u003Cbr\u003EUse the ? in situations where you do not need a formal parameter type like \u003C T \u003E\u003Cbr\u003E\u003Cp\u003EData type is not required here\u003Cbr\u003E","\u003Cp\u003EBe careful\u003Cbr\u003E\u003Cp\u003EHolder\u003C?\u003E h = new Holder\u003CString\u003E();\u003Cbr\u003Eh.add(new Object()); \u002F\u002F compile time error\u003Cbr\u003Eh.add(new String()); \u002F\u002F compile time error\u003Cbr\u003E\u002F\u002F one exception!\u003Cbr\u003Eh.add(null); \u002F\u002F null is member of every type\u003Cbr\u003E\u003Cbr\u003EWorking with unbounded wildcards we can only read data, not assign!\u003Cbr\u003E\u003Cbr\u003E","\u003Cp\u003EUpper - Bound Wildcards\u003Cbr\u003E\u003Cp\u003EBounded wildcards put some restrictions on unknown type:\u003Cbr\u003Epublic static void printList(List\u003C? extends Number\u003E list){\u003Cbr\u003E for(Number x : list) {\u003Cbr\u003E System.out.println(x.doubleValue());\u003Cbr\u003E }\u003Cbr\u003E list.add(new Integer(3)); \u002F\u002F compile error\u003Cbr\u003E}\u003Cbr\u003E\u003Cp\u003ENow we know that object is instance of Number\u003Cbr\u003E\u003Cp\u003EBut we still don’t know exact type, so can’t modify list\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? extends Animal\u003E animal) {\u003Cbr\u003E animal.get().check(); \u002F\u002F OK\u003Cbr\u003E animal.set(new Cat()); \u002F\u002F Error: we don’t know exact parameter type of animal\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat = new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003ELower Bounded Wildcards\u003Cbr\u003E\u003Cp\u003Ea lower bounded wildcard restricts the unknown type to be a specific type or a super type of that type\u003Cbr\u003EHolder\u003C? super Integer\u003E h = new Holder\u003CInteger\u003E();\u003Cbr\u003Eh.add(new Integer(1));\u003Cbr\u003EInteger i1 = h.get(); \u002F\u002F compilation error\u003Cbr\u003E\t\t\t\u002F\u002F get returns Object\u003Cbr\u003EInteger i2 = (Integer)h.get(); \u002F\u002F OK\u003Cbr\u003ELower bounded wildcards allow to modify but not read!!\u003Cbr\u003E","\u003Cp\u003EExample\u003Cbr\u003E\u003Cp\u003Epublic static void addNumbers(List\u003C? super Integer\u003E list) {\u003Cbr\u003E for (int i = 1; i \u003C= 10; i++) {\u003Cbr\u003E list.add(i);\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003EList\u003CInteger\u003E i = new ArrayList\u003CInteger\u003E();\u003Cbr\u003EList\u003CNumber\u003E n = new ArrayList\u003CNumber\u003E();\u003Cbr\u003EList\u003CObject\u003E o = new ArrayList\u003CObject\u003E();\u003Cbr\u003E\t\t\u003Cbr\u003EaddNumbers(i);\u003Cbr\u003EaddNumbers(n);\u003Cbr\u003EaddNumbers(o);\u003Cbr\u003EThis works fine\u003Cbr\u003E","\u003Cp\u003EMore example\u003Cbr\u003Eclass AnimalDoctor {\u003Cbr\u003E void checkAnimal(Holder\u003C? super Dog\u003E dog) {\u003Cbr\u003E animal.get().check(); \u002F\u002F Error!\u003Cbr\u003E \u002F\u002F get() returns Object ref\u003Cbr\u003E animal.set(new Dog()); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CAnimal\u003E animal = new Holder\u003CAnimal\u003E();\u003Cbr\u003E Holder\u003CCat\u003E cat= new Holder\u003CCat\u003E();\u003Cbr\u003E AnimalDoctor doctor = new AnimalDoctor();\u003Cbr\u003E doctor.checkAnimal(dog); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(animal); \u002F\u002F OK\u003Cbr\u003E doctor.checkAnimal(cat); \u002F\u002FError: Cat isn’t super of Dog\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EWhat's the difference?\u003Cbr\u003Evoid check(Holder\u003C?\u003E holder) { }\u003Cbr\u003Evoid check(Holder\u003CObject\u003E holder) { }\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003CObject\u003E obj) {\u003Cbr\u003E obj.set(new Dog());\u003Cbr\u003E obj.set(new Cat());\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CObject\u003E obj = new Holder\u003CObject\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(obj); \u002F\u002F Only Holder\u003CObject\u003E goes here!\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E","\u003Cp\u003EThere IS a huge difference!\u003Cbr\u003Eclass Main {\u003Cbr\u003E void check(Holder\u003C?\u003E obj) {\u003Cbr\u003E obj.set(new Dog()); \u002F\u002F Error\u003Cbr\u003E \u002F\u002F Compiler isn't sure that it's really Dog Holder\u003Cbr\u003E }\u003Cbr\u003E public static void main(String[] args) {\u003Cbr\u003E Holder\u003CDog\u003E dog = new Holder\u003CDog\u003E();\u003Cbr\u003E Holder\u003CInteger\u003E integer = new Holder\u003CInteger\u003E();\u003Cbr\u003E Main main = new Main();\u003Cbr\u003E main.check(dog); \u002F\u002F OK\u003Cbr\u003E main.check(integer); \u002F\u002F OK\u003Cbr\u003E }\u003Cbr\u003E}\u003Cbr\u003E",I,I,"\u003Cp\u003ENaming Conventions for Generics\u003Cbr\u003E\u003Cp\u003EE for an element\u003Cbr\u003EK for a map key\u003Cbr\u003EV for a map value\u003Cbr\u003EN for a number\u003Cbr\u003ET for a generic data type\u003Cbr\u003EUse S , U , V , and so on for multiple types in the same class.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E1) Generics let you enforce compile-time type safety.\u003Cbr\u003EHolder\u003CString\u003E h1 = new Holder\u003CString\u003E();\u003Cbr\u003EHolder h2 = new Holder();\u003Cbr\u003EString s = h1.get(); \u002F\u002F no cast needed\u003Cbr\u003EString s = (String) h2.get(); \u002F\u002F cast required\u003Cbr\u003E2) Generic type information does not exist at runtime — it is for compile-time safety only.\u003Cbr\u003E3) Polymorphic assignment don't apply to the generic type\u003Cbr\u003EHolder\u003CAnimal\u003E h1 = new Holder\u003CDog\u003E(); \u002F\u002F Error\u003Cbr\u003E4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:\u003Cbr\u003Evoid foo(List\u003CDog\u003E d) {} \u002F\u002F can take only \u003CDog\u003E\u003Cbr\u003Evoid foo(List\u003C? extends Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CCollie\u003E\u003Cbr\u003Evoid foo(List\u003C? super Dog\u003E) {} \u002F\u002F take a \u003CDog\u003E or \u003CAnimal\u003E\u003Cbr\u003E5) When using a wildcard, List\u003C? extends Dog\u003E, the collection can be accessed but not modified.\u003Cbr\u003E","\u003Cp\u003ESummary\u003Cbr\u003E6) The generics type identifier can be used in class, method, and variable declarations:\u003Cbr\u003E class Foo\u003Ct\u003E { } \u002F\u002F a class\u003Cbr\u003E T anInstance; \u002F\u002F an instance variable\u003Cbr\u003E Foo(T aRef) {} \u002F\u002F a constructor argument\u003Cbr\u003E void bar(T aRef) {} \u002F\u002F a method argument\u003Cbr\u003E T baz() {} \u002F\u002F a return type\u003Cbr\u003E7) You can use more than one parameterized type in a declaration:\u003Cbr\u003E public class UseTwo\u003CT, X\u003E { }\u003Cbr\u003E8) You can declare a generic method using a type not defined in the class:\u003Cbr\u003E public \u003CT\u003E T returnMe(T t) { return t; }\u003Cbr\u003EReading in Russian\u003Cbr\u003Ehttp:\u002F\u002Fwww.rsdn.ru\u002Farticle\u002Fjava\u002Fgenericsinjava.xml\u003Cbr\u003E"],href:"\u002Finformatika\u002Fgenerics-lecture-73",href_category:"\u002Finformatika",date:1628090801,related:[{id:404222,name:"Научно-техническая информация",href:"\u002Finformatika\u002Fnauchno-tehnicheskaya-informatsiya-1",jpg:"jpg\u002F404222"},{id:478755,name:"Презентация к аттестации учителя информатики",href:"\u002Finformatika\u002Fprezentatsiya-k-attestatsii-uchitelya-informatiki",jpg:"jpg\u002F478755"},{id:4499,name:"Основные компоненты ПК",href:"\u002Finformatika\u002Fosnovnye-komponenty-pk",jpg:"jpg\u002F4499"},{id:184558,name:"Арифметические основы организации ЭВМ",href:"\u002Finformatika\u002Farifmeticheskie-osnovy-organizatsii-evm",jpg:"jpg\u002F184558"},{id:373746,name:"Вёрстка и дизайн газетной статьи",href:"\u002Finformatika\u002Fvyorstka-i-dizayn-gazetnoy-stati",jpg:"jpg\u002F373746"},{id:577279,name:"Алгоритм действий родителей для прохождения регистрации их детей младше\u002Fстарше 14 лет во ФГИС Моя школа",href:"\u002Finformatika\u002Falgoritm-deystviy-roditeley-dlya-prohozhdeniya-registratsii",jpg:"jpg\u002F577279"},{id:12068,name:"Керування правами доступу",href:"\u002Finformatika\u002Fkeruvannya-pravami-dostupu",jpg:"jpg\u002F12068"},{id:403270,name:"Понятие алгоритма, свойства, виды (типы). Формы записи. Исходные и выходные данные алгоритмов, примеры (Лекция 3)",href:"\u002Finformatika\u002Fponyatie-algoritma-svoystva-vidy-tipy-formy",jpg:"jpg\u002F403270"},{id:234266,name:"Взаимодействие клиента и сервера",href:"\u002Finformatika\u002Fvzaimodeystvie-klienta-i-servera",jpg:"jpg\u002F234266"},{id:266792,name:"Как с нуля запустить Онлайн-школу",href:"\u002Finformatika\u002Fkak-s-nulya-zapustit-onlayn-shkolu",jpg:"jpg\u002F266792"},{id:104353,name:"Программа Project Expert",href:"\u002Finformatika\u002Fprogramma-project-expert",jpg:"jpg\u002F104353"},{id:3725,name:"What is cryptocurrency",href:"\u002Finformatika\u002Fwhat-is-cryptocurrency",jpg:"jpg\u002F3725"},{id:1966,name:"История развития и поколения СУБД. Классификация СУБД. Архитектура СУБД. Основные компоненты СУБД",href:"\u002Finformatika\u002Fistoriya-razvitiya-i-pokoleniya-subd-klassifikatsiya",jpg:"jpg\u002F1966"},{id:253599,name:"WORD-тын графикалык мумкіндіктері",href:"\u002Finformatika\u002Fword-tyn-grafikalyk-mumkndkter",jpg:"jpg\u002F253599"},{id:215026,name:"Компьютер как универсальное устройство обработки информации",href:"\u002Finformatika\u002Fkompyuter-kak-universalnoe-ustroystvo-obrabotki-informatsii",jpg:"jpg\u002F215026"},{id:200593,name:"Линейное программирование",href:"\u002Finformatika\u002Flineynoe-programmirovanie-2",jpg:"jpg\u002F200593"},{id:429765,name:"ОУ Новоселецкая школа. Навигатор дополнительного образования Омской области",href:"\u002Finformatika\u002Fou-novoseletskaya-shkola-navigator-dopolnitelnogo-obrazovaniya",jpg:"jpg\u002F429765"},{id:383037,name:"Социальная память. Функция социальной памяти",href:"\u002Finformatika\u002Fsotsialnaya-pamyat-funktsiya-sotsialnoy-pamyati",jpg:"jpg\u002F383037"},{id:160929,name:"Різновиди діаграм та їх форматування",href:"\u002Finformatika\u002Frznovidi-dagram-ta-h-formatuvannya",jpg:"jpg\u002F160929"},{id:266355,name:"Лекция 2. Файлы (текстовые). Массивы",href:"\u002Finformatika\u002Flektsiya-2-fayly-tekstovye-massivy",jpg:"jpg\u002F266355"},{id:610347,name:"3D моделирование в программе Tinkercad",href:"\u002Finformatika\u002F3d-modelirovanie-v-programme-tinkercad",jpg:"jpg\u002F610347"},{id:393791,name:"Load testing with Visual Studio Enterprise 2015",href:"\u002Finformatika\u002Fload-testing-with-visual-studio-enterprise",jpg:"jpg\u002F393791"},{id:114799,name:"Информация, ее свойства. Информация и управление",href:"\u002Finformatika\u002Finformatsiya-ee-svoystva-informatsiya-i-upravlenie",jpg:"jpg\u002F114799"},{id:435506,name:"Информационные технологии в ДОУ",href:"\u002Finformatika\u002Finformatsionnye-tehnologii-v-dou",jpg:"jpg\u002F435506"},{id:439332,name:"Security. The goal",href:"\u002Finformatika\u002Fsecurity-the-goal",jpg:"jpg\u002F439332"},{id:15166,name:"Интернет желісіне жалпы сипаттама",href:"\u002Finformatika\u002Finternet-zhelsne-zhalpy-sipattama",jpg:"jpg\u002F15166"},{id:326320,name:"Особенности работы с информацией в различных типах источников. Лекция 3",href:"\u002Finformatika\u002Fosobennosti-raboty-s-informatsiey-v-razlichnyh",jpg:"jpg\u002F326320"},{id:503963,name:"Презентация к уроку информатики в 5 классе по теме Метод координат",href:"\u002Finformatika\u002Fprezentatsiya-k-uroku-informatiki-v-5-6",jpg:"jpg\u002F503963"}],navigation:{next:"\u002Fliteratura\u002Ftragediya-gyote-faust-2",next_name:"Трагедия Гёте Фауст",prev:"\u002Finformatika\u002Finternet-technologies-2",prev_name:"Internet technologies"}}},categories:{result:[{id:J,ordering:b,name:"Без категории",pseudoname:"uncategorized"},{id:H,ordering:b,name:"Бизнес",pseudoname:"biznes"},{id:146,ordering:b,name:"Образование",pseudoname:"obrazovanie"},{id:149,ordering:b,name:"Финансы",pseudoname:"finansy"},{id:150,ordering:b,name:"Государство",pseudoname:"gosudarstvo"},{id:152,ordering:b,name:"Спорт",pseudoname:"sport"},{id:154,ordering:b,name:"Армия",pseudoname:"armiya"},{id:156,ordering:b,name:"Культурология",pseudoname:"kulturologiya"},{id:157,ordering:b,name:"Еда и кулинария",pseudoname:"eda-i-kulinariya"},{id:158,ordering:b,name:"Лингвистика",pseudoname:"lingvistika"},{id:163,ordering:b,name:"Черчение",pseudoname:"cherchenie"},{id:164,ordering:b,name:"Физкультура",pseudoname:"fizkultura"},{id:165,ordering:b,name:"ИЗО",pseudoname:"izo"},{id:166,ordering:b,name:"Психология",pseudoname:"psihologiya"},{id:116,ordering:J,name:"Английский язык",pseudoname:"angliyskiy-yazyk"},{id:108,ordering:2,name:"Астрономия",pseudoname:"astronomiya"},{id:104,ordering:3,name:"Алгебра",pseudoname:"algebra"},{id:106,ordering:4,name:"Биология",pseudoname:"biologiya"},{id:142,ordering:5,name:"География",pseudoname:"geografiya"},{id:141,ordering:6,name:"Геометрия",pseudoname:"geometria"},{id:123,ordering:7,name:"Детские презентации",pseudoname:"detskie-prezentatsii"},{id:107,ordering:8,name:G,pseudoname:"informatika"},{id:109,ordering:9,name:"История",pseudoname:"istoriya"},{id:139,ordering:10,name:"Литература",pseudoname:"literatura"},{id:119,ordering:11,name:"Маркетинг",pseudoname:"marketing"},{id:114,ordering:12,name:"Математика",pseudoname:"matematika"},{id:138,ordering:h,name:"Медицина",pseudoname:"medetsina"},{id:118,ordering:14,name:"Менеджмент",pseudoname:"menedzhment"},{id:137,ordering:15,name:"Музыка",pseudoname:"muzyka"},{id:136,ordering:16,name:"МХК",pseudoname:"mhk"},{id:130,ordering:17,name:"Немецкий язык",pseudoname:"nemetskiy-yazyk"},{id:105,ordering:18,name:"ОБЖ",pseudoname:"obzh"},{id:133,ordering:19,name:"Обществознание ",pseudoname:"obshchestvoznanie"},{id:132,ordering:20,name:"Окружающий мир ",pseudoname:"okruzhayushchiy-mir"},{id:131,ordering:21,name:"Педагогика ",pseudoname:"pedagogika"},{id:129,ordering:22,name:"Русский язык",pseudoname:"russkiy-yazyk"},{id:128,ordering:24,name:"Технология",pseudoname:"tehnologiya"},{id:127,ordering:25,name:"Физика",pseudoname:"fizika"},{id:126,ordering:26,name:"Философия",pseudoname:"filosofiya"},{id:125,ordering:27,name:"Химия",pseudoname:"himiya"},{id:124,ordering:29,name:"Экология",pseudoname:"ekologiya"},{id:121,ordering:30,name:"Экономика",pseudoname:"ekonomika"},{id:120,ordering:31,name:"Юриспруденция",pseudoname:"yurisprudentsiya"}]}},state:{},_errors:{},serverRendered:e,config:{public:{SITE_NAME:K,SITE_HOST:"mypreza.com",SITE_LANG:L,API_BASE_URL:"https:\u002F\u002Fmypreza.com\u002Fapi\u002F",pwaManifest:{name:K,short_name:a,description:a,lang:L,start_url:"\u002F?standalone=true",display:"standalone",background_color:j,theme_color:"#000000",icons:[{src:"\u002F_nuxt\u002Ficons\u002F64x64.f2a6e93d.png",type:d,sizes:M,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F64x64.maskable.f2a6e93d.png",type:d,sizes:M,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F120x120.f2a6e93d.png",type:d,sizes:N,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F120x120.maskable.f2a6e93d.png",type:d,sizes:N,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F144x144.f2a6e93d.png",type:d,sizes:O,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F144x144.maskable.f2a6e93d.png",type:d,sizes:O,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F152x152.f2a6e93d.png",type:d,sizes:P,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F152x152.maskable.f2a6e93d.png",type:d,sizes:P,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F192x192.f2a6e93d.png",type:d,sizes:Q,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F192x192.maskable.f2a6e93d.png",type:d,sizes:Q,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F384x384.f2a6e93d.png",type:d,sizes:R,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F384x384.maskable.f2a6e93d.png",type:d,sizes:R,purpose:g},{src:"\u002F_nuxt\u002Ficons\u002F512x512.f2a6e93d.png",type:d,sizes:S,purpose:f},{src:"\u002F_nuxt\u002Ficons\u002F512x512.maskable.f2a6e93d.png",type:d,sizes:S,purpose:g}]},yandexMetrika:{id:"85004146",metrikaUrl:"https:\u002F\u002Fmc.yandex.ru\u002Fmetrika\u002Ftag.js",accurateTrackBounce:e,childIframe:c,clickmap:c,defer:c,useRuntimeConfig:e,trackHash:c,trackLinks:e,type:b,webvisor:c,triggerEvent:c,consoleLog:e,partytown:c,isDev:c}},app:{baseURL:"\u002F",buildAssetsDir:"\u002F_nuxt\u002F",cdnURL:a}},pinia:{app:{meta:{h1:l,main_text:a,main_title:m,main_description:n,main_keywords:o,main_image:a},app:{logo_image:p,logo_image_width:q,logo_image_height:r,logo_text:a,image_width_full:s,image_width_min:t,recaptcha_key:u,yandex_search:v,ya_context:c,banner_1:a,banner_2:a,banner_3:a,banner_4:a,banner_5:a,banner_6:a,banner_7:a,banner_8:a,banner_9:a,banner_10:a,email:w,footer_before:a,footer:a,dark_theme:c,strategy:{image_alt_words:h,item_slide_header:x,item_images:y,item_images_tag:z,item_words_h3:c,item_words_tag:A,item_words_1:h,routing:B,item_slide_skipping:C,item_download_timeout:D,item_slider_width:E,item_show_pdf:e,item_show_contents:e,item_show_filename:e},colors:{header_text:j,header_bg:i,accent:i}},social:F,token:a}}}}("",0,false,"image\u002Fpng",true,"any","maskable",13,"#d53032","#ffffff","Generics. (Lecture 7.3)","Учебные презентации","Презентации в PowerPoint на разные темы","Презентации, проекты, доклады в PowerPoint на разные темы для учебы","Презентация, на тему, урок, класс, PowerPoint, скачати презентацію, фон, шаблон, доклад, проект.","images\u002Fdata\u002Flogo.png",185,40,720,480,"6LeioWIpAAAAAGqMN4KqMVIkekcMW7fBKHjXCd-a","2503267","[e-mail]","h3a","text","none","h3","category","both",80,800,"\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fes5-shims\u002F0.0.2\u002Fes5-shims.min.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cscript src=\"\u002F\u002Fyastatic.net\u002Fshare2\u002Fshare.js\"\u003E\u003C\u002Fscript\u003E\r\n\u003Cdiv class=\"ya-share2\" data-services=\"collections,gplus,vkontakte,facebook,odnoklassniki,gplus,twitter,moimir\" data-counter=\"\"\u003E\u003C\u002Fdiv\u003E","Информатика",144,"\u003Cp\u003EWhich will compile?\u003Cbr\u003E1) List\u003C?\u003E list = new ArrayList\u003CDog\u003E();\u003Cbr\u003E2) List\u003C? extends Animal\u003E aList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E3) List\u003C?\u003E foo = new ArrayList\u003C? extends Animal\u003E();\u003Cbr\u003E4) List\u003C? extends Dog\u003E cList = new ArrayList\u003CInteger\u003E();\u003Cbr\u003E5) List\u003C? super Dog\u003E bList = new ArrayList\u003CAnimal\u003E();\u003Cbr\u003E6) List\u003C? super Animal\u003E dList = new ArrayList\u003CDog\u003E();\u003Cbr\u003E",1,"Mypreza","ru","64x64","120x120","144x144","152x152","192x192","384x384","512x512"))

There IS a huge difference!
class Main {
void check(Holder
obj) {
obj.set(new Dog()); // Error
// Compiler isn't sure that it's really Dog Holder
}
public static void main(String[] args) {
Holder
dog = new Holder
();
Holder
integer = new Holder
();
Main main = new Main();
main.check(dog); // OK
main.check(integer); // OK
}
}

Which will compile?
1) List
list = new ArrayList
();
2) List
aList = new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();

Which will compile?
1) List
list = new ArrayList
();
2) List
aList = new ArrayList
();
3) List
foo = new ArrayList
();
4) List
cList = new ArrayList
();
5) List
bList = new ArrayList
();
6) List
dList = new ArrayList
();

Naming Conventions for Generics
E for an element
K for a map key
V for a map value
N for a number
T for a generic data type
Use S , U , V , and so on for multiple types in the same class.

Summary
1) Generics let you enforce compile-time type safety.
Holder
h1 = new Holder
();
Holder h2 = new Holder();
String s = h1.get(); // no cast needed
String s = (String) h2.get(); // cast required
2) Generic type information does not exist at runtime — it is for compile-time safety only.
3) Polymorphic assignment don't apply to the generic type
Holder
h1 = new Holder
(); // Error
4) Wildcard syntax allows a generic method, accept subtypes (or supertypes) of the declared type of the method argument:
void foo(List
d) {} // can take only
void foo(List
) {} // take a
or
void foo(List
) {} // take a
or
5) When using a wildcard, List
, the collection can be accessed but not modified.