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 {

    public void faHongbao(){
        System.out.println("大舅不仅发红包，还送烟");

    }

    public void chouyan(){
        System.out.println("大舅喜欢抽烟");
    }


}

子类二：

public class UncleTwo {
    public void faHongbao(){
        System.out.println("二舅不仅发红包，还送酒");

    }
}

多态

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

    }


}

用父类接受子类的对象，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 class Demo {
    public static void main(String[] args){
        Uncle uncle1= new UncleOne();
        //uncle1.chouyan(); 不能调用

向上转型

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

向下转型

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

instanceof

判断对象是否给定的类的实例

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