public class Test {

   public  static  void  main(String [] args){

    Plate<? extends Fruit> p = new Plate<Apple>(new Apple());

       Food food = p.get();

       Fruit fruit = p.get();

     //ERROR

//       p.set(new Fruit());

//       p.set(new Orange());

//       p.set(new Apple());

    //error

    //  Apple apple = p.get();

Plate<? super Fruit> p1 = new Plate<Fruit>(new Fruit());

p1.set(new Apple());

p1.set(new Orange());

p1.set(new Fruit());

Object object = p1.get();

   }

}

class Plate<T>{

    private T item;

    public Plate(T t){

        item = t;

    }

    public T get() {

        return item;

    }

    public void set(T item) {

        this.item = item;

    }

}

//父类

class Food {

    void eatFood(){

        System.out.println("eatFood");

    }

}

//子类1

class Fruit extends Food{

    void eatFruit(){

        System.out.println("eatFruit");

    }

}

class Meat extends Food{

    void eatMeat(){

        System.out.println("eatMeat");

    }

}

//子类2

class Apple extends Fruit{

    void eatApple(){

        System.out.println("eatApple");

    }

}

class Orange extends Fruit{

    void eatOrange(){

        System.out.println("eatOrange");

    }

}

class Pork extends Meat{

    void eatPork(){

        System.out.println("eatPork");

    }

}

class Beaf extends Meat{

    void eatBeaf(){

        System.out.println("eatBeaf");

    }

}