### 多态
父类
```java
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
UncleTwo 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 子类独有的方法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
instanceof
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 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();
}
}
}
