instanceof operator vs isInstance() method in Java

instanceof operator and isInstance() method both are used for checking the class of the object. But main difference comes when we want to check the class of object dynamically. In this case isInstance() method will work. There is no way we can do this by instanceof operator.

instanceof operator and isInstance() method both return a boolean value. Consider an example:

// Java program to demonstrate working of 
// instanceof operator 
public class Test 
{ 
    public static void main(String[] args) 
    { 
        Integer i = new Integer(5); 
  
        // prints true as i is instance of class 
        // Integer 
        System.out.println(i instanceof Integer); 
    } 
} 

Output:

true

Now if we want to check the class of the object at run time, then we must use isInstance() method.

// Java program to demonstrate working of isInstance() 
// method 
public class Test 
{ 
    // This method tells us whether the object is an 
    // instance of class whose name is passed as a 
    // string 'c'. 
    public static boolean fun(Object obj, String c) 
                      throws ClassNotFoundException 
    { 
        return Class.forName(c).isInstance(obj); 
    } 
  
    // Driver code that calls fun() 
    public static void main(String[] args) 
                      throws ClassNotFoundException 
    { 
        Integer i = new Integer(5); 
  
        // print true as i is instance of class 
        // Integer 
        boolean b = fun(i, "java.lang.Integer"); 
  
        // print false as i is not instance of class 
        // String 
        boolean b1 = fun(i, "java.lang.String"); 
  
        /* print true as i is also instance of class 
           Number as Integer class extends Number 
           class*/
        boolean b2 = fun(i, "java.lang.Number"); 
  
        System.out.println(b); 
        System.out.println(b1); 
        System.out.println(b2); 
    } 
} 

Output:

true
false
true

NOTE: instanceof operator throws compile time error(Incompatible conditional operand types) if we check object with other classes which it doesn’t instantiate.

public class Test 
{ 
    public static void main(String[] args) 
    { 
        Integer i = new Integer(5); 
  
        // Below line causes compile time error:- 
        // Incompatible conditional operand types 
        // Integer and String 
        System.out.println(i instanceof String); 
    } 
} 

Output :

13: error: incompatible types: Integer cannot be converted to String
        System.out.println(i instanceof String);
                           ^

This article is contributed by Gaurav Miglani. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

My Personal Notes

Recommended Posts: