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("大舅喜欢送烟");
    }
}

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

public class Demo {
    public static void main(String[] args) {
        //多态
        Uncle uncle1=new UncleOne();
        uncle1.faHongbao();
        //向上转型
        Uncle uncle2=new UncleTwo();
        uncle2.faHongbao();
    }
}

用父类接收子类的对象，只能调用父类中出现过的方法，子类的扩展的独有方法无法调用

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

向上转型

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

向下转型

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

instanceof

判断对象是否是指定的类的实例

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 UncleTwo){
            UncleTwo u2=(UncleTwo) uncle1;
            u2.faHongbao();
        }
        if (uncle1 instanceof UncleOne){
            UncleOne u1=(UncleOne) uncle1;
            u1.faHongbao();
            u1.chouyan();
        }
    }
}