Question

instanceof can be used to test if an object is a direct or descended instance of a given class. instanceof can also be used with interfaces even though interfaces can’t be instantiated like classes. Can anyone explain how instanceof works?

Answer 1

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’