instanceof关键字

instanceof关键字是一个双目运算符，用来判断一个对象是否是该类的实例

boolean result = obj instanceof Class

 

1、obj必须为引用类型，不能为基本类型

int i = 0;

System.out.println(i.instanceof(Integer));//return false

System.out.println(i.instanceof(Object));//return false

2、obj为null则返回false

System.out.println(null.instanceof(Object));//return false

3、obj为class类的实例对象

Integer i = new Integer();

System.out.println(i.instanceof(Integer));//return true

4、obj为接口的实现类

ArrayList arrayList = new ArrayList();

System.out.println(arrayList.instanceof(List));//return true

List list = new ArrayList();

System.out.println(list.instanceof(ArrayList));//return true

5、obj为类的直接或间接子类

class Person{

}

class Man extends Person{

}

Person person1  = new Person();

Person person2 = new Man();

Man man = new Man();

System.out.println(person1.instanceof(Man));//return false

System.out.println(person2.instanceof(Man));//return true

System.out.println(man.instanceof(Man));//return true