Java 形参和返回值

1 . 类作为形参和返回值: 该类作为对象

//类作为形参: 该类作为对象

public class Cat{
    public void eat(){
    System.out.println("猫吃东西");
    }
}



public class CatOperator{

    public void uesCat(Cat c){

        c.eat();
    }
}

public class CatDome{

    public static void main(String[] args){

        CatOperator co = new CatOperator();
        Cat c = new Cat();
        co.useCat(c);
    }
}

//类名作为返回值

public Cat getCat(){

    Cat c = new Cat();
    return c;
}

2. 抽象类名作为形参和返回值:  该抽象类的子类对象

//抽象类名作为形参: 抽象类的子类对象


public abstract class Animal{

    public abstract void eat();
}

//抽象类父类Animal不能实例化,多态形式传递eat方法
//Cat类
public class Cat extends Animal{
    @Override         //重写Animaleat方法
    System.out.println("猫吃鱼");
}


//AnimalOperator类
public class AnimalOperator{
    public void useAnimal(Animal a){        //创建对象 Animal a = new Animal();
        a.eat();
    }

    public Animal getAnimal(){
        Animal a = new Cat();
        return a;
    }
}


//AnimalDemo类

public class AnimalDemo{

    public static void main(String[] atgs){
        AnimalOperator ao = new AnimalOperator();
        Animal a = new Cat();
        ao.uesCat(a);

        Animal a2 = ao.getAnimal();        //Aniaml a2 = new Cat()
        a2.eat();
    }
}

3. 接口名作为形参和返回值

//

public interface Jumppinp{

    void jump();
}


//接口的操作类
public class JumppingOperator{

    //形参是接口:该接口的实现类对象Jumpping j = new Cat();
    public void useJumpping(Jumpping j){        

        j.jump();
    }
    
    public Jumpping getJumpping(){        //返回型是接口名,返回的是接口的实现类对象
        Jumpping j = new Cat();
        return j;
    }

}


//Cat类(接口不能实例化,创建一个类去实现实例化)
public class Cat extends Jumpping{
    @Override 
    public void jump(){
        System.out.println("猫跳高");
    }
}


//测试类
public class JumppingDemo{

    public static void main(String[] args){
        //创建操作类对象,并调用方法
        JumppingOperator jo = new JumppingOperator();
        Jumpping j = new Cat();
        jo.useJumpping(j);

        Jumpping j2 = jo.getJumpping();    //new Cat()
        j2.jump();
    }
}