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
public interface Person {
public void eat();
}
实现类People
public class People implements Person {
private int a=0;
@Override
public void eat() {
System.out.println("======"+a);
}
}
子类xiaoming：
public class xiaoming extends People {
private String name;
@Override
public void eat() {
System.out.println("+++++++++");
}
}
主函数
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：
true false true true
实例2
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：
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：
总结
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