JAVA基础-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为抽象类,

3. 抽象类必须被继承, 抽象方法必须被重写

4. 抽象类不能被实例化

5. 抽象方法只需声明, 不需要实现.

如果派生类派生了个抽象子类不想实现抽象方法, 可以将自己设定为abstract,可以不用重写抽象方法, 让继承他的子类再去重写方法.

abstract class Animal {
  private String name;
  Animal(String name) {this.name = name;}
  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("猫叫声......");
  }
}
 
class Dog extends Animal {
  private String furColor;
  Dog(String n,String c) {super(n); furColor = c;}
 
  public void enjoy() {
    System.out.println("狗叫声......");
  }
}
 
class Bird extends Animal {
	 Bird() {
	 	 super("bird");
	 }
	 public void enjoy() {
    System.out.println("鸟叫声......");
  }
}
 
class Lady {
    private String name;
    private Animal pet;
    Lady(String name,Animal pet) {
        this.name = name; this.pet = pet;
    }
    public void myPetEnjoy(){pet.enjoy();}
}
 
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();
    }
}