Java-instanceof关键字

一、instanceof

　　在编写代码过程中，如果不知道一个对象属于哪一个类，这时instanceof关键字起到决定性作用，他会以boolean（true\false）反馈结果

class A{
    public void fun1(){
        System.out.println("A----->public void fun1");
    }
    public void fun2(){
        this.fun1();
    }
}
class B extends A{
    public void fun1(){  //覆写父类fun1方法
        System.out.println("B-->public void fun1(B)");
    }
    public void fun3(){
        System.out.println("B---->public void fun3(B)");
    }
}
class C extends A{
    public void fun1(){ //覆写父类fun1方法
        System.out.println("C---->public void fun1(C)");
    }
    public void fun5(){
        System.out.println("C------>public void fun5(C)");
    }
}
public class DomeA {
    public static void main(String[] args){

        A a1 = new B(); //通过向上转型实例化A类对象
        System.out.println("A a1 = new B():"+(a1 instanceof A));
        System.out.println("A a1 = new B():"+(a1 instanceof B));

        A a2 = new A();  //通过A类的构造实例化本类对象
        System.out.println("A a2 = new A():"+(a2 instanceof A));
        System.out.println("A a2 = new A():"+(a2 instanceof B));
    }
}
//A a1 = new B():true
//A a1 = new B():true
//A a2 = new A():true
//A a2 = new A():false