Singleton Pattern

• Resource: http://www.patterndepot.com/put/8/Singleton.PDF
• The singleton pattern allows you to insure that a class can only be instantiated one time.
• What you need to do:
• Declare the constructor private.  Thus, the class cannot be instantiated by anyone but itself, since only it has  access to the constructor.
• A static attribute of the same type as the class, that holds the single object of the class.
• Provide a static method that returns the single instance of the class. Why a static method?  Thus, it will need to have a return type of the class itself.  It should first check the static attribute (above) to see if the object has been instantiated - it is likely that it will not be the first time it is called.
• If it has been instantiated, simply return that object from the static attribute.
• If not, instantiate an object, save it to the static variable listed above, and return it.
• This is most commonly used with single instances, but you can maintain a small number of instances the same way.
• Example.

Created by:  Brandan Jones December 17, 2001