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Replies:  3

Singleton Design Pattern


I have a question about the Singleton design pattern.

Is Singleton pattern about maintaining one instance of a class or is it about maintaining one state of a class. What I can think of is this: if it's about creating one instance of a class then static classes are not a way of implementing Singleton design pattern. But if it's about maintaining one state of a class then there is nothing like monostate pattern.

Please advice.
Ram Pandey, May 16, 2010
Reply 1

Go through this link, you will have better understanding of singleton pattern
Bhupendra Sinha, May 21, 2010
Reply 2
Some differences between Singletons and Static classes are...

* Singletons can implement interfaces

* You cannot pass a static class as a parameter to a method, this can be done with a Singleton

* A Singleton is a normal class that is instantiated just once, a static class is never instantiated

As a side note, I usually tend not to use either of these. Instead I use my DI container (Ninject, StructureMap, ...) to supply me with a singleton of the required type when needed.
Robert Blixt, May 17, 2010
Reply 3
Singleton Pattern is a creational pattern and is all about making sure we have only one instance (maximum) of a class at any given point in time.

It just needs a private constructor so that none of the external instances can directly create an instance of the singleton class under consideration. This Singleton class needs to expose one public method eg: GetInstance, which intenally calls the private constuctor only if there is no preexisting instance of the class. Lock statements can be used in the implementation to avoid any hassles of multi-threaded access to the Singleton.

Sreenivas Manyam Rajaram, May 16, 2010
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