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, ...
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