How to implement a Singleton design pattern in IBM Rational Rhapsody

Answer

Singleton Design Pattern

Requirements

1. The class must contain static instance representing the single instance
2. The class must define a public accessor function to allow client access to the instance.
3. The public accessor must implement "Lazy Initialization"; Only initializing the instance when it is needed.
4. The class must not define public access constructors.

Solution

You can model the implementation by using a self-referencing aggregation association. Note that a composition would be invalid here as a self-referencing composition would create a recursive relationship.

The Counter singleton class is not to instantiated directly. It manages it's own "lazy initialization" via the Counter::instance() method by instantiating the static member.

Internal Counter Variable is updated in the Counter Statechart. To begin execution you therefore, use the following call:

Counter::instance()->startBehavior();


This is called in the Main File.