Comments on: How and when to use Singleton classes

By: MCPHERSONStaci24

MCPHERSONStaci24 — Wed, 21 Jul 2010 18:53:46 +0000

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By: Alzheimers Disease

Alzheimers Disease — Tue, 15 Jun 2010 10:01:55 +0000

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By: Anonymous

Anonymous — Sat, 22 May 2010 13:47:44 +0000

what will be the scenario when a singleton will not be singleton. OR What are the drawbacks of singleton ?

By: LearningCoder

LearningCoder — Thu, 18 Feb 2010 13:03:54 +0000

For a full fledged implementation clone() should also be overriden and cloneNotSupportedException should be thrown.

By: arun

arun — Wed, 10 Feb 2010 17:13:52 +0000

Thanks.
Really good one .

By: Satish

Satish — Mon, 08 Feb 2010 15:27:10 +0000

@teo If you try to use this(Singleton)in other class how will you get instance of it(new Singleton())? A static method of return type instance should be present.

By: Anonymous

Anonymous — Mon, 17 Aug 2009 13:51:08 +0000

@Jordi In the newer Java compilers a Singleton instance is not initialized until it is first used.

By: Jordi

Jordi — Tue, 17 Mar 2009 23:27:45 +0000

You say that it is better not to use a static class if you need state. Why can’t you just use static variables?

@teo:
1) The instance would need to be public.
2) A small downside of this is that now Singleton is always initialized, even if it isn’t used.

By: teo

teo — Tue, 17 Mar 2009 08:46:12 +0000

The initialization of instance is verbose and not thread-safe.
How about this :

public class Singleton {
private static final Singleton instance = new Singleton();
private Singleton(){}
}

Or even better:

public enum Singleton {
INSTANCE;
}

(see Bloch’s Effective Java, 2nd edition).

By: Carsten Schlipf

Carsten Schlipf — Fri, 20 Feb 2009 20:00:56 +0000

Assuming that you singleton pattern is written in Java, note that the code is not thread-safe as long as you make the getInstance() method synchronized.