```java
//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 fangHongbao(){
        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  UncleTow extends Uncle {
    public void fangHongbao(){
        System.out.println("二舅不仅发红包，还送酒");
    }
}

多态

public class demo {
    public static void main(String[] args) {
        
        /*  UncleOne uncleOne=new UncleOne();
        uncleOne.faHongbao();
        UncleTow uncleTow=new UncleTow();
        uncleTow.faHongbao();*/
        
        //多态
        Uncle uncle1 = new UncleOne();
        uncle1.faHongbao();

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

//用父类的类名接受子类创建的对象，只能调用父类中出现过的方法

public class demo {
    public static void main(String[] args) {
        Uncle uncle1 = new UncleOne();
        //uncle1,chouyan(); 不能调用
    }
}

        Uncle uncle2 = new UncleTow(); //向上转型
        uncle2.faHongbao();//大舅发红包

    Uncle uncle1 = new UncleOne();
        UncleOne u1 = (UncleOne) uncle1; //向下转型
        u1.fangHongbao();
        u1.chouyan;//可以调用

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

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