java中instanceof和getClass()的区别

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：

package a_start._11_instanceof;

class Base{
    
}
class Derived extends Base{
    
}

public class TestInstanceof {
    public static void main(String[] args) {
        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().equals(Derived.class);//true
//      bRet = d.getClass() == Base.class;// 出错 Incompatible operand types ,可以强转(Object)就不报错了
        bRet = d.getClass().equals(Base.class);//false
        
        //boolean java.lang.Class.isInstance(Object obj)
        // true if obj is an instance of this class
        System.out.println(Derived.class.isInstance(d));//true
        System.out.println(Base.class.isInstance(d));//true
        
        
        //扩展
        System.out.println(String.class instanceof Class);//true  对象String.class 是 Class的实例
        System.out.println("test" instanceof String);//true
        
        System.out.println("\"test\".getClass().isInstance(Object.class):"+("test".getClass().isInstance(Object.class)));
        System.out.println("\"test\".getClass().isInstance(String.class):"+("test".getClass().isInstance(String.class)));
        System.out.println("String.class.isInstance(Object.class):"+(String.class.isInstance(Object.class)));
        System.out.println("String.class.isInstance(String.class):"+(String.class.isInstance(String.class)));
        System.out.println("\"test\".getClass().getClass().isInstance(Object.class):"
                +("test".getClass().getClass().isInstance(Object.class)));
        System.out.println("\"test\".getClass().getClass().isInstance(String.class):"
                +("test".getClass().getClass().isInstance(String.class)));
        System.out.println("String.class.getClass().isInstance(Object.class):"
                +(String.class.getClass().isInstance(Object.class)));
        System.out.println("String.class.getClass().isInstance(String.class):"
                +(String.class.getClass().isInstance(String.class)));
        
        /*
"test".getClass().isInstance(Object.class):false   // "test".getClass() 等价于 String.class
"test".getClass().isInstance(String.class):false  //表示 对象String.class 是String的实例吗，显然不是 String.class 是Class的实例
String.class.isInstance(Object.class):false
String.class.isInstance(String.class):false
"test".getClass().getClass().isInstance(Object.class):true
"test".getClass().getClass().isInstance(String.class):true
String.class.getClass().isInstance(Object.class):true  //  Class<? extends Class>
String.class.getClass().isInstance(String.class):true  // 表示 String.class 是 Class<? extends String> 实例， 是Class<? extends Class>的子类实例
         */
    }
}

 

 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;
    }
}

 判断是否为空

    private static Boolean IsNullOrEmpty(Object obj) {
        if(null == obj)
            return false;
        if(obj instanceof String) { // 是字符串 ，也可以用 String.class.isInstance(obj)
            return ((String)obj).trim().length() == 0;
        }
        if(obj instanceof Object[]) {//是数组(不包括基本类型数组，像 int[]),  或用 obj.getClass().isArray() 
            return ((Object[])obj).length == 0;
        }
        if(obj instanceof java.util.Collection) { //是集合（包括java.util.List，Set, Queue, 等子类 ）
            return 0 == ((java.util.Collection)obj).size();
        }
        if(obj instanceof java.util.Map) { // 是map
            return 0 == ((java.util.Map)obj).size();
        }
        
        return false;
    }

 

 

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