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about singleton classes uses

4 replies on 1 page. Most recent reply: Jun 3, 2004 12:32 AM by Shashank D. Jha

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sweth_murali

Posts: 3
Nickname: sweth
Registered: May, 2004

about singleton classes uses

Posted: Jun 1, 2004 12:17 AM

can anyone tell in which scenario we are using singleton classes and what is the use of singleton classes.

mausam

Posts: 243
Nickname: mausam
Registered: Sep, 2003

Re: about singleton classes uses

Posted: Jun 2, 2004 3:41 AM

Anywhere, where u dont want multiple instance of ur class (or for that matter u want fixed maximum number of instances) of ur class, u go for Singleton class. properties and variables for such class can be shared only to one client.

Shashank D. Jha

Posts: 68
Nickname: shashankd
Registered: May, 2004

Re: about singleton classes uses

Posted: Jun 2, 2004 8:07 AM

Singleton class ensures that at any instance of time there is only one object of its type exists.

Now the scenarios wherein you would like to use it where by any chance you don want to allow someone to create more then one instance, example

object of "President" of USA. (President is a class)

You will also use this pattern to control some specific behaiour that cannot be circumvented ex.

to ensure that every object within application share common time make Time class as singleton.

Singleton class also enables greated control on the way object may behave.

you may and will find several more reasons wherein you require singleton behaviour of a class.

hope this helps.

regards,
Shashank

Jai

Posts: 5
Nickname: jarulraj
Registered: Apr, 2004

Re: about singleton classes uses

Posted: Jun 3, 2004 12:16 AM

What are the issues in having a singleton in the app server ? Like if two references happen simultaneously ?

Shashank D. Jha

Posts: 68
Nickname: shashankd
Registered: May, 2004

Re: about singleton classes uses

Posted: Jun 3, 2004 12:32 AM

Well, it should not happen, unless singleton is not implemented properly.

Issues that may arise depends on the criticality of behaviour defined for that singleton class. Remr two presidents of USA!!

Or two threads now trying to change the state of data base objects (while data base objects were not thread safe) and were expecting co-operation from singleton class instance that were implementing thread safe feature.

So issues that may and can arise are immense depending on behaviour put within singleton class.

regards,
Shashank

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