java中instanceof和getClass()的区别

Posted 2020-12-18

htj10

tags:

对象 instanceof 类名，表示 对象是类名的实例，或者是其子类的实例，返回 true，否则返回 false。
对象.getClass() == 类名.class ，表示 只有对象是该类的实例，才返回 true

 

class A { }

class B extends A { }

Object o1 = new A();
Object o2 = new B();

o1 instanceof A => true
o1 instanceof B => false
o2 instanceof A => true // <================ HERE
o2 instanceof B => true

o1.getClass().equals(A.class) => true
o1.getClass().equals(B.class) => false
o2.getClass().equals(A.class) => false // <===============HERE
o2.getClass().equals(B.class) => true  

getClass() will be useful when you want to make sure your instance is NOT a subclass of the class you are comparing with.

例子：

class Base{
    
}
class Derived extends Base{
    
}

public class Hello {
    public static void main(String[] args) throws ParseException {
        Derived d = new Derived();
        boolean bRet;
        bRet = d instanceof Derived;//true
        bRet = d instanceof Base;//true
        bRet = d.getClass() == Derived.class;//true
//      bRet = d.getClass() == Base.class;// 出错
        bRet = d.getClass().equals(Base.class);//false
    }
}

 使用，重写equals

class Person{
    private String id;
    private String name;
    //重写equals()方法，提供自定义的相等标准
    public boolean equals(Object obj){
        if(this == obj)//若为同一个对象
            return true;
        //只有当obj是Person对象
        if(null != obj && obj.getClass() == Person.class){
            Person p = (Person)obj;
            if(id.equals(obj).getId() && ...){
                return true;
            }
        }
        return false;
    }
}

 

另外：[Java] Java instanceof 和 Class.isInstance()区别与应用