java之抽象类

1、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，该方法叫做抽象方法。

2、含有抽象方法的类必须被声明抽象类，抽象类必须被继承，抽象方法必须被重写。

3、抽象类不能被实例化。

4、抽象方法只需声明，而不需实现。

public class TestPolymorphic{
    public static void main(String args[]){
    
        //Animal animal = new Animal("animal");            抽象类不能被实例化
        Cat cat = new Cat("cat","blue");
        Dog dog = new Dog("dog","black");
        
        //Lily l1 = new Lily("l1",animal);
        Lily l2 = new Lily("l2",dog);
        
        //l1.myAnimalEnjoy();
        l2.myAnimalEnjoy();
    }
}
class Lily{
    private String name;
    private Animal animal;
    public Lily(String name, Animal animal){
        this.name = name;
        this.animal = animal;
    }
    public void myAnimalEnjoy(){
        animal.enjoy();
    }
}
abstract class Animal{                    //声明抽象类
    private String name;
    public Animal(String name){
        this.name = name;
    }
    /*public void enjoy(){
        System.out.println("叫声~~~");
    }*/
    public abstract void enjoy();        //声明抽象方法
}
class Dog extends Animal{
    
    private String forlorColor;
    public Dog(String name,String forlorColor){
        super(name);
        this.forlorColor = forlorColor;
    }
    public void enjoy(){
        System.out.println("dog叫声~~~");
    }
}
class Cat extends Animal{
    
    private String eyesColor;
    public Cat(String name,String eyesColor){
        super(name);
        this.eyesColor = eyesColor;
    }
    public void enjoy(){
        System.out.println("cat叫声~~~");
    }
}

运行结果：

总结：抽象类一般是用在多态。