Singleton
pattern is a popular design pattern which proposes that only one instance of a class will be created by JVM.Repeated calls always return the same instance.When programmers need to be concerned about meaningful use of resource then use this pattern.For example ,if programmers create a new connection object every time it requires , then clearly it is a wastage of resource.In this case we can create a singleton connection class and that single connection object will be used throughout the application.
If you need connection object just use it like this....
Another example where singleton is used frequently is in hibernate when you instanciate SessionFactory.Because SessionFactory is very resource intensive.So instanciate it only once.
I hope this will help you.For more info go to this link
Singleton Pattern