Marker Interface???

[Rohit VG]

What is the use of a marker interrface if it has no contents???
eg. Serializable interface.

[Paul Sturrock]

This gets asked a lot. Search the "Java in General (beginner)" forum, you'll find plenty of answers.

[Ravinder S Edhan]

Hi,

It's not like that 'marker interface' does nothing? If you dig inside this 'Serializable' interface, you will come to know how does this work. There are 'writeObject' and 'readObject' kind of methods hidden behind the scene.

regards

[Paul Sturrock]

Originally posted by Ravinder S Edhan:

If you dig inside this 'Serializable' interface, you will come to know how does this work.

Ehm, no you won't. It is a marker interface, it has no source code that does anything. Below is a truncated version of the source code for Serializable (I've removed the comments to save space):

/*
 * @(#)Serializable.java    1.20 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
 
package java.io;
 
/**
 *  (comments removed)
 */
public interface Serializable {
}

[Ernest Friedman-Hill]

Moving to Java in General (Beginner).

[Stan James]

A marker interface is there just so we can ask an object if it has the marker. In this case a serializer might have a whole collection of objects or one object that has references to a bunch of others. The serializer can ask each object "Do you want to be serialized?" If the marker interface is not present, the serializer skips it.

Do you know how to test if an object implements an interface? See if you can find a Java operator to do the job!