Singleton Pattern

Singleton Design pattern is one of the simplest and most common patterns that exists. It is part of Creational Design Patterns. Its goal is to ensure that only one instance of an object could be created.

There are many examples for cases where you would need an object to be instantiated only once:

• Managers - For example a WindowManager
• Engines - For example Dependency Resolver Engine
• Factories, Loggers, Configurators and etc.

Implementation

The implementation of Singleton is very simple. You need three things:

• Static member of the class
• Private constructor
• Public method to return the instantiated static member

class Singleton
{
	private static Singleton instance;
	private Singleton()
	{
		// Some code
	}

	public static Singleton getInstance()
	{
		if (instance == null)
			instance = new Singleton();

		return instance;
	}
	
	// Methods
}

The usage of this Singleton class is very simple as well.

Singleton instance = Singleton.getInstance();
instance.DoSomethingMethod();