Singleton Design Pattern

This is one of the most simple Design Pattern.

Singleton Design pattern restricts the instantiation of a class to only one object.

Real life usage includes creating only one database connection which can be shared by multiple objects. Also, one thing that needs to be considered for such scenario is making the connection thread safe.

Pitfalls

• This pattern is often overused. Because of the simplicity and power of singleton, people tends to make everything singleton when it doesn't necessarily need to be.

• This pattern makes unit testing difficult.

• Not thread-safe, if not implemented correctly.

Contrast to Factory pattern

Singleton	Factory
Returns same instance.	Returns various instances
No interface	Interface driven
One constructor method - no args	Multiple constructors
	Adaptable to environment more easily

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