How to write our own marker interface in Java?

Question

I know marker interface in java. It is used to define a specific behaviour about a class. For example, Serializable interface has the specific ability to store an object into by

Answer 1

Marker interface has no method. Java has built-in marker interface like Serializable, Clonable & EventListner etc that are understand by JVM.

We can create our own marker interface, but it has nothing to do with JVM, we can add some checks with instanceOf.

1. Create the empty interface

   interface Marker{    }
   

2. Write a class and implements the interface

   class A implements Marker {
       //do some task
   }
   

3. Main class to check the marker interface instanceof

   class Main {
       public static void main(String[] args) {
           A ob = new A(){
           if (ob instanceof A) {
               // do some task
           }
       }
   }