1. Java Generics? ?? ??

Java Generics? ???? ?? ????? ???? ???, ????? ? ???? ??? ? ????. ?? ??? ??? ?? ???? ????? ??? ??? ??? ???? ??? ??? ? ??? ?????.

1.1 ????? ??????

???? ???? ??? ??? ?? ?? ???? ???? ???, ????? ?? ???? ??? ? ??? Java 5? ??? ?????. ?? ??? ?? ?? ???? ????? ?? ???? ??? ? ?? ??? ? ???? ???? ? ??? ???.

?:

public class Box<T> {
    private T value;

    public void setValue(T value) {
        this.value = value;
    }

    public T getValue() {
        return value;
    }
}

? ??? T? Box? ????? ??? ? ?? ??? ???? ??? ? ?? ?? ???????.

1.2 ? Generic? ??????

???? ?? ?? ??? ?????.

• ?? ???: ??? ??? ?? ???? ???? ???? ?? ??? ??? ??? ????.
• ?? ????: ??? ??? ??? ??? ? ?? ?? ???? ???? ?? ? ????.
• ??? ??: ???? ???? ?? ???? ???? ???? ??? ? ???? ?? ?? ???? ?????.

?:

??? ??:

List list = new ArrayList();
list.add("Hello");
String s = (String) list.get(0); // Casting needed

??? ??:

List<String> list = new ArrayList<>();
list.add("Hello");
String s = list.get(0); // No casting needed

2. ????? ??? ??

?? ???? ???? ???? ?? ???? ???? ?? ??? ? ????. ??? ???? ???? ????? ???? ??? ??? ????.

2.1 ?? ??? ?

?? ??? ? ?? ???? ?? ??? ?? ??? ???.

public class Pair<K, V> {
    private K key;
    private V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    public K getKey() {
        return key;
    }

    public V getValue() {
        return value;
    }
}

? ??? K? V? pair? ????? ??? ? ??? ? ?? ?? ???????.

?? ?:

Pair<String, Integer> pair = new Pair<>("Age", 30);
System.out.println("Key: " + pair.getKey() + ", Value: " + pair.getValue());

2.2 ??? ?? ????

??? ?? ???? ???? ?? ??? ? ?? ??? ???? ?? ?? ????. ??? ?? ????? ???? ???? ??? ??? ??? ? ????.

?:

public class NumberUtils {
    public static <T extends Number> void printNumber(T number) {
        System.out.println("Number: " + number);
    }
}

??? T? Integer, Double ?? ?? Number? ?? ???? ?????.

?? ?:

NumberUtils.printNumber(10); // Valid
NumberUtils.printNumber(10.5); // Valid

3. ???? ???

???? ????? ???? ????. ???? ??? ??? ???? ??? ?? ???? ??? ?? ????.

3.1 ???? ??? ?

??? ? ?? ? ? ???? ???? ??????.

public class Util {
    public static <T extends Comparable<T>> T max(T a, T b) {
        return a.compareTo(b) > 0 ? a : b;
    }
}

? ???? T? T? ??? ? ??? Comparable? ???? ?? ?? ???????.

?? ?:

public class Box<T> {
    private T value;

    public void setValue(T value) {
        this.value = value;
    }

    public T getValue() {
        return value;
    }
}

3.2 ???? ?????

?????? ???? ???? ??? ??? ?? ???? ??? ? ????. ?? ??, ? ?? T? T? ???? ? ? ?? ??? ????, ? super T? T? ?? ??? ? ? ?? ??? ?????.

?:

List list = new ArrayList();
list.add("Hello");
String s = (String) list.get(0); // Casting needed

?? ?:

List<String> list = new ArrayList<>();
list.add("Hello");
String s = list.get(0); // No casting needed

4. ??

Java Generics? ????? ??? ???? ???? ?? ??? ? ????. ???, ??? ? ??????? ???? ???? ??? ???? ?? ???? ??? ??? ??? ??? ? ????. ??? ??? ?? ??? ??? ?? ??? ??? ?????!

?? ? ?? ???? ?????. Java Generics ?????: ?? ??? ??? ?? ???

? ??? Java Generics ?????: ?? ??? ??? ?? ???? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!