Design Pattern - Singleton

Singleton

Definition 

Singleton pattern is a software design pattern that restricts the instantiation of a class to one single instance. This is useful when exactly one object is needed to coordinate actions across the system. 

Common usage of Singleton pattern 

  • Single database object shared by different parts of the program 
  • Logging object. 
  • Replacement of global variables, since Singleton instances doesn't pollute namespace and has lazy initialization attribute. 

Singleton with code 

  1. We will define a single Singleton instance that will be instantiated statically. 
  2. We will prevent Singleton instance from being created by default constructor by private access modifier. That way, there is no way to create singleton instance using new keyword. 
  3. There must be a way to retrieve Singleton instance. We will create a static method getInstance(), that will enable us to retrieve the same Singleton instance whenever we request them. 

REFERENCE 

https://en.wikipedia.org/wiki/Singleton_pattern

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