本文研究的主要是java中instanceof与Class的等价性的相关问题,具体如下。
java 中的instanceof 运算符是用来在运行时指出对象是否是特定类的一个实例。instanceof通过返回一个布尔值来指出,这个对象是否是这个特定类或者是它的子类的一个实例。
实例1(instanceof)
接口Person
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public interface Person { public void eat(); } |
实现类People
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public class People implements Person { private int a= 0 ; @Override public void eat() { System.out.println( "======" +a); } } |
子类xiaoming:
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public class xiaoming extends People { private String name; @Override public void eat() { System.out.println( "+++++++++" ); } } |
主函数
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public static void main(String[] args) { People p= new People(); xiaoming x= new xiaoming(); System.out.println(p instanceof Person); System.out.println(p instanceof xiaoming); ----- 2 System.out.println(x instanceof Person); System.out.println(x instanceof People); } |
注意:上面2处的代码在编译时不会报错。
运行结果:
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true false true true |
实例2
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package com.test.class_obj; class Base { } class Derived extends Base { } public class FamilyVsExactType { static void test(Object x) { System.out.println( "Testing x of type " + x.getClass().getSimpleName()); System.out.println( "-----------------------------------------" ); System.out.println( "x instanceof Base " + (x instanceof Base)); System.out.println( "x instanceof Derived " + (x instanceof Derived)); System.out.println( "-----------------------------------------" ); System.out.println( "Base.isInstance(x) " + Base. class .isInstance(x)); System.out.println( "Derived.isInstance(x) " + Derived. class .isInstance(x)); System.out.println( "-----------------------------------------" ); System.out.println( "x.getClass() == Base.class " + (x.getClass() == Base. class )); System.out.println( "x.getClass() == Derived.class " + (x.getClass() == Derived. class )); System.out.println( "x.getClass().equals(Base.class)) " + (x.getClass().equals(Base. class ))); System.out.println( "x.getClass().equals(Derived.class)) " + (x.getClass().equals(Derived. class ))); System.out.println( "*****************************************" ); System.out.println( "*****************************************" ); } public static void main(String[] args) { test( new Base()); test( new Derived()); } } |
输出内容如下:
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Testing x of type Base ----------------------------------------- x instanceof Base true x instanceof Derived false ----------------------------------------- Base.isInstance(x) true Derived.isInstance(x) false ----------------------------------------- x.getClass() == Base. class true x.getClass() == Derived. class false x.getClass().equals(Base. class )) true x.getClass().equals(Derived. class )) false ***************************************** ***************************************** Testing x of type Derived ----------------------------------------- x instanceof Base true x instanceof Derived true ----------------------------------------- Base.isInstance(x) true Derived.isInstance(x) true ----------------------------------------- x.getClass() == Base. class false x.getClass() == Derived. class true x.getClass().equals(Base. class )) false x.getClass().equals(Derived. class )) true ***************************************** ***************************************** Process finished with exit code 0 |
通过以上测试可以得出以下结论:
- instanceof() 和 isInstance() 生成的结果相同
- equals() 和 == 生成的结果相同
- 父类可以是子类的实例,但子类不可以是父类的实例
- Class 对象比较时,不考虑继承
总结
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原文链接:http://blog.csdn.net/heatdeath/article/details/79099861