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Marker Interface???

Rohit VG
Greenhorn

Joined: Oct 26, 2005
Posts: 2
What is the use of a marker interrface if it has no contents???
eg. Serializable interface.
Paul Sturrock
Bartender

Joined: Apr 14, 2004
Posts: 10336

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


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Ravinder S Edhan
Ranch Hand

Joined: Dec 15, 2003
Posts: 57
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
Bartender

Joined: Apr 14, 2004
Posts: 10336

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):
Ernest Friedman-Hill
author and iconoclast
Marshal

Joined: Jul 08, 2003
Posts: 24184
    
  34

Moving to Java in General (Beginner).


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Stan James
(instanceof Sidekick)
Ranch Hand

Joined: Jan 29, 2003
Posts: 8791
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!


A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi
 
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