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Java学习 - 黑马(第二部分) - 随堂笔记 - 06_形参和返回值

君心浅语 2022-04-16 阅读 46

Java学习 - 黑马(第二部分) - 随堂笔记 - 06_形参和返回值

形参和返回值

1.1 类名作为形参和返回值

  • 方法的形参是类名,其实需要的是该类的对象
  • 方法的返回值是类名,其实返回的是该类的对象
package com.itheima_01;

public class Cat {
    public void eat(){
        System.out.println("猫吃鱼");
    }
}
package com.itheima_01;

public class CatOperator {
    public void useCat(Cat c){
        c.eat();
    }

    public Cat getCat(){
        Cat c = new Cat();
        return c;
    }
}
package com.itheima_01;

public class CatDemo {
    public static void main(String[] args) {
        //创建操作类对象,并调用方法
        CatOperator co = new CatOperator();
        Cat c = new Cat();
        co.useCat(c);

        Cat c2 = co.getCat();
        c2.eat();
    }
}

1.2 抽象类名作为形参和返回值

  • 方法的形参是抽象类名,其实需要的是抽象类的子类对象
  • 方法的返回值是抽象类名,其实返回的是该抽象类的子类对象
package com.itheima_02;

public abstract class Animal {
    public abstract void eat();
}
package com.itheima_02;

public class Cat extends Animal{
    @Override
    public void eat() {
        System.out.println("猫吃鱼");
    }
}
package com.itheima_02;

public class AnimalOperator {
    public void useAnimal(Animal a){//Animal a = new Cat;
        a.eat();
    }
    public Animal getAnimal(){
        Animal a = new Cat();
        return a;
    }
}
package com.itheima_02;

public class AnimalDemo {
    public static void main(String[] args) {
        //创建操作类对象,并调用方法
        AnimalOperator ao = new AnimalOperator();
        Animal a = new Cat();
        ao.useAnimal(a);

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

1.3 接口作为形参和返回值

  • 方法的形参是接口名,其实需要的是该接口的实现类对象
  • 方法的返回值是接口名,其实返回的是该接口的实现类对象
package com.itheima_03;

public interface Jumpping {
    void jump();
}
package com.itheima_03;

public class Cat implements Jumpping{
    @Override
    public void jump() {
        System.out.println("猫可以跳高了" );
    }
}
package com.itheima_03;

public class JumppingOperator {
    public void useJumpping(Jumpping j){//Jumpping j = new Cat();
        j.jump();
    }
    public Jumpping getJumpping(){
        Jumpping j = new Cat();
        return j;
    }
}
package com.itheima_03;

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();
    }
}
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