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

• How JVM invoke this specific behavior

ObjectOutputStream and ObjectInputStream will check your class whether or not it implementes Serializable, Externalizable. If yes it will continue or else will thrown NonSerializableException.

• How to write our own marker interface

Create an interface without any method and that is your marker interface.

Sample

public interface IMarkerEntity {


}

If any class which implement this interface will be taken as database entity by your application.

Sample Code:

public boolean save(Object object) throws InvalidEntityException {
   if(!(object instanceof IMarkerEntity)) {
       throw new InvalidEntityException("Invalid Entity Found, cannot proceed");
   } 
   database.save(object);
}

• Is this possible to have methods in marker interface?

The whole idea of Marker Interface Pattern is to provide a mean to say "yes I am something" and then system will proceed with the default process, like when you mark your class as Serialzable it just tells that this class can be converted to bytes.