How instanceof will work on an interface

First of all, we can store instances of classes that implements a particular interface in an interface reference variable like this.

package com.test;

public class Test implements Testable {

    public static void main(String[] args) {

        Testable testable = new Test();

        // OR

        Test test = new Test();

        if (testeable instanceof Testable)
            System.out.println("instanceof succeeded");
        if (test instanceof Testable)
            System.out.println("instanceof succeeded");
    }
}

interface Testable {

}

ie, any runtime instance that implements a particular interface will pass the instanceof test

EDIT

and the output

instanceof succeeded
instanceof succeeded

@RohitJain

You can create instances of interfaces by using anonymous inner classes like this

Runnable runnable = new Runnable() {
    
    public void run() {
        System.out.println("inside run");
    }
};

and you test the instance is of type interface, using instanceof operator like this

System.out.println(runnable instanceof Runnable);

and the result is 'true'

You do an instanceof check of a reference against an instance, and it checks the type of instance that particular reference is pointing to.

Now since you can create a reference of an interface, which points to an instance of implementing class (same concept as, Super class reference pointing to subclass instance). So, you can do an instanceof check on it.

For e.g :-

public interface MyInterface {
}

class ImplClass implements MyInterface {

    public static void main(String[] args) {
        MyInterface obj = new ImplClass();

        System.out.println(obj instanceof ImplClass);   // Will print true.
    }
}

object instanceof object_interface will yield true.