多态

父类

public class Uncle {
    private String name;
    private int age;

    public void faHongbao(){
        System.out.println("舅舅发红包");
    }
}

子类一：

public class UncleOne extends Uncle{

    public void faHongbao(){
        System.out.println("大舅不仅发红包，还送烟");
    }

    public void chouyan(){
        System.out.println("大舅喜欢抽烟");
    }

}

子类二：

public class UncleTwo extends Uncle{
    
    public void faHongbao(){
        
        System.out.println("二舅不仅发红包，还送酒");
    }
    
}

启动类

多态

//多态
Uncle uncle1 = new UncleOne();
uncle1.faHongbao();
Uncle uncle2 = new UncleTwo();//向上转型
uncle2.faHongbao();

用父类接受子类的对象，只能调用父类中出现过的方法，子类的扩展的都有方法无法调用

public class Demo {
    public static void main(String[] args) {
        Uncle uncle1 = new UncleOne();
        //uncle1.chouyan();  不能用
        }

向上转型

Uncle uncle2 = new UncleTwo();//向上转型
uncle2.faHongbao();

向下转型

Uncle uncle1 = new UncleOne();
UncleOne u1 = (UncleOne) uncle1;//向下转型
u1.faHongbao();
u1.chouyan();

instanceof

判断对象是否是给定的类的实例

作用：避免类型转换时，出现错误，进而引发程序的崩溃

ublic class Demo01 {
    public static void main(String[] args) {
        Uncle uncle1 = new UncleOne();
        if (uncle1 instanceof UncleTwo){
            UncleTwo u2 = (UncleTwo) uncle1;
            u2.faHongbao();
        }
        if (uncle1 instanceof UncleOne){
            UncleOne u1 =(UncleOne) uncle1;
            u1.faHongbao();
            u1.chouyan();
        }

    }
}