抽象类

用abstract关键字来修饰一个类时，这个类叫做抽象类；用abstract来修饰一个方法时，这个方法叫抽象方法。

含有抽象方法的类必须被声明为抽象类，抽象类必须被继承，抽象方法必须被重写。

抽象类不能被实例化。

抽象方法只需声明，而不需要实现。

例如下

public class Test {
    public static void main(String args[]) {
        
        Cat c = new Cat("catname","blue");
        Dog d = new Dog("dogname","black");
        Bird b = new Bird();
        
        Lady l1 = new Lady("l1",c);
        Lady l2 = new Lady("l2",d);
        Lady l3 = new Lady("l3",b);
        
        
        l1.myPetEnjoy();
        l2.myPetEnjoy();
        l3.myPetEnjoy();
        
    }
}


//定义抽象类
abstract class Animal {
    private String name;
    Animal(String name) {
        this.name = name;
    }
    
    /*public void enjoy() {
        System.out.println("动物叫声........");
    }*/
    public abstract void enjoy();
}

class Cat extends Animal {
    private String eyesColor;
    Cat(String n,String c) {super(n); eyesColor = c;}
    public void enjoy() {
        System.out.println("喵喵喵............");
    }
    
}

class Dog extends Animal {
    private String furColor;
    Dog(String n,String c) {super(n); furColor = c; }
    public void enjoy() {
        System.out.println("汪汪汪............");
    }
}

class Bird extends Animal {
    Bird() {
        super("bird");
    }
    public void enjoy() {
        System.out.println("叽叽喳喳..........");
    }
}


class Lady {
    private String name;
    private Animal pet;   //定义Animal类型的pet
    Lady(String name,Animal pet) {
        this.name = name; this.pet = pet;
    }
    public void myPetEnjoy() {pet.enjoy();}

}