java中的instanceof用法详解

  instanceof是Java的一个二元操作符(运算符),也是Java的保留关键字。它的作用是判断其左边对象是否为其右边类的实例,返回的是boolean类型的数据。用它来判断某个对象是否是某个Class类的实例。

用法:

  boolean result = object instanceof class

参数:

  result :boolean类型。

  object :必选项。任意对象表达式。

  class:必选项。任意已定义的对象类。

说明:

  如果该object 是该class的一个实例,那么返回true。如果该object 不是该class的一个实例,或者object是null,则返回false。

例子:

  package com.instanceoftest;
  interface A { } 
  class B implements A { } //B是A的实现
  class C extends B { } //C继承B
  class D { }
  class instanceoftest {
    public static void main(String[] args) {
      A a = null;
      B b = null;
      boolean res;
      System.out.println("instanceoftest test case 1: ------------------");
      res = a instanceof A;
      System.out.println("a instanceof A: " + res); // a instanceof A:false
      res = b instanceof B;
      System.out.println("b instanceof B: " + res); // b instanceof B: false
 
      System.out.println("\ninstanceoftest test case 2: ------------------");
      a = new B();
      b = new B();
      res = a instanceof A;
      System.out.println("a instanceof A: " + res); // a instanceof A:true
      res = a instanceof B;
      System.out.println("a instanceof B: " + res); // a instanceof B:true
      res = b instanceof A;
      System.out.println("b instanceof A: " + res); // b instanceof A:true
      res = b instanceof B;
      System.out.println("b instanceof B: " + res); // b instanceof B:true
 
      System.out.println("\ninstanceoftest test case 3: ------------------");
      B b2 = new C();
      res = b2 instanceof A;
      System.out.println("b2 instanceof A: " + res); // b2 instanceof A:true
      res = b2 instanceof B;
      System.out.println("b2 instanceof B: " + res); // b2 instanceof A:true
      res = b2 instanceof C;
      System.out.println("b2 instanceof C: " + res); // b2 instanceof A:true
 
      
      System.out.println("\ninstanceoftest test case 4: ------------------");
      D d = new D();
      res = d instanceof A;
      System.out.println("d instanceof A: " + res); // d instanceof A:false
      res = d instanceof B;
      System.out.println("d instanceof B: " + res); // d instanceof B:false
      res = d instanceof C;
      System.out.println("d instanceof C: " + res); // d instanceof C:false
      res = d instanceof D;
      System.out.println("d instanceof D: " + res); // d instanceof D:true
    }
  }
 

 

posted @ 2017-06-28 16:33  史迪仔。  阅读(30253)  评论(0编辑  收藏