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
}
}