java 泛型

class Point<T>{
    private T a;
    private T b;
    public Point(T a, T b){
        this.a = a;
        this.b = b;
    }
    public void say(){
        System.out.println("a: " + a + ", b: " + b);
    }
}
public class Test3 {
    public static void main(String[] args) {
        Point<Integer> point1 = new Point<>(1, 2);
        point1.say();
        Point<String> point2 = new Point<>("hello", "world");
        point2.say();
    }
}

interface IPoint<T>{
    void say(T t);
}
class PointImpl1 implements IPoint<String>{
    @Override
    public void say(String s) {
        System.out.println(s);
    }
}

class PointImpl2<T> implements IPoint<T>{
    @Override
    public void say(T t) {
        System.out.println(t);
    }
}
public class Test3 {
    public static void main(String[] args) {
        IPoint p1 = new PointImpl1();
        p1.say("Hello");
        IPoint<Integer> p2 = new PointImpl2<>();
        p2.say(1);
    }
}

public static void main(String[] args) {
        String s = say("hello");
        System.out.println(s);
    }

    // 返回类型由参数决定
    public static <T> T say(T t){
        return t;
    }