多态

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("大舅发红包");
    }
    public void songyan(){
        System.out.println("大舅喜欢送烟");
    }
}

子类二：

public class UncleTwo extends Uncle{

    public void fahongbao(){
        System.out.println("二舅发红包");
    }
}

多态

UncleOne dajiu=new UncleOne();
dajiu.fahongbao();//大舅发红包
Uncle uncleTwo=new UncleTwo();
uncleTwo.fahongbao();//二舅发红包

向上转型

Uncle dajiu1=new UncleOne();
dajiu1.fahongbao();//大舅发红包

向下转型

Uncle dajiu1=new UncleOne();
dajiu1.fahongbao();
//dajiu1.songyan(); //会报错 子类独有的方在发生向上转型的时候无法在父类中使用
UncleOne temp=(UncleOne)dajiu1;//向下转型
        temp.songyan();//可以调用子类独有的方法

instancesof

判断对象是否是指定的类型的实例

避免发生错误的类型转换
public class Demo01 {

public static void main(String[] args) {

    Uncle uncle1=new UncleOne();
    Uncle uncle2=new UncleTwo();
    if(uncle1 instanceof UncleOne){
        UncleOne u1=(UncleOne) uncle1;
        u1.fahongbao();
    }
    if (uncle2 instanceof UncleTwo){

        UncleTwo u2=(UncleTwo) uncle2;
        u2.fahongbao();
    }
}