SE450: Creational Patterns: Singleton [7/12]

• Name - Singleton
• Intent - Ensure a class has only one instance, and provide global access to it
• Problem -
  • There must be only one instance of a class, and it must be accessible from a known point
  • The sole instance should be accessible by subclassing, and clients should still be able to access the instance without modifying code.
• Solution - Allow only one instance of the object to be created, and provide access to it through a static method.
• Participants and Collaborators
  • Singleton
• Consequences
  • Controlled access to sole instance
  • Reduced name space
  • Permits refinement of operations and representation - the instance may be selected at run time, as an example
  • Permits a variable number of instances
  • More flexible that just using static access (think about method hiding...)
• Implementation
  • Ensuring a unique instance
  • Subclassing the Singleton class
• GoF Reference (127)
• Example files are here