多態(tài)

父類

public class Uncle {
    private String name;
    private int age;
    public void faHongbao() {
        System.out.println("舅舅發(fā)紅包");
    }
}

子類一：

public class UncleOne extends Uncle{

    public void faHongbao() {
        System.out.println("大舅發(fā)紅包");
    }
    public void songYan() {
        System.out.println("大舅喜歡送煙");
    }

}

子類二：

public class UncleTwo extends Uncle{
    public void faHongbao() {
        System.out.println("二舅發(fā)紅包");
    }
}

多態(tài)

        UncleOne dajiu = new UncleOne();
        dajiu.faHongbao();  // 大舅發(fā)紅包
        UncleTwo uncleTwo = new UncleTwo();
        uncleTwo.faHongbao();  // 二舅發(fā)紅包

向上轉型

        Uncle dajiu1 = new UncleOne();
        dajiu1.faHongbao();  // 大舅發(fā)紅包

向下轉型

        Uncle dajiu1 = new UncleOne();
        dajiu1.faHongbao();
      //dajiu1.songYan();   // 會報錯 子類獨有的方法在發(fā)生向上轉型的時候無法在父類中使用
        UncleOne temp = (UncleOne) dajiu1;  // 向下轉型
        temp.songYan();  // 可以調用子類獨有的方法

instanceof

判斷對象是否是指定的類型的實例

避免發(fā)生錯誤的類型轉換

public class Demo02 {
    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();
        }
    }
}