Introducing the Singleton Pattern

According to the Gang of Four, the Singleton's intent is to

Ensure a class only has one instance, and provide a global point of access to it.^[2]

^[2] Gamma, E., Helm, R., Johnson, R., Vlissides, J., Design Patterns: Elements of Reusable Object-Oriented Software, Reading, Mass.: Addison-Wesley, 1995, p. 127.

The Singleton pattern works by having a special method that is used to instantiate the desired object.

• When this method is called, it checks to see if the object has already been instantiated. If it has, the method simply returns a reference to the object. If not, the method instantiates it and returns a reference to the new instance.

• To ensure that this is the only way to instantiate an object of this type, I define the constructor of this class to be protected or private.