Singleton Design Pattern

Singleton Design Pattern: (Factory Design Pattern here)
What is Singleton Design Pattern?
Singleton Design pattern makes sure that there is only one instance of class is created and restricts developers to create multiple instances of same class.

Why do we need Singleton Design Pattern?
Singleton Design pattern is used when we have to limit the system for only one instance.  This is used when we have to share some resources and to use specific resource the program should cross this point.

Steps for Creating Singleton Class:

  • The instance should be private static final to make it singleton
  • Constructor should be private (to restrict the instantiation of object directly)
  • public static method for callers to get reference

Example:

Difference Between Static and Singleton Class:

Static Singleton
Greater Performance (since static is used at compile time) Less performance when compared to static
Static class is eagerly loaded Singleton class can be lazy loaded


Disadvantages of Singleton Design
Pattern:

  • Singleton classes cannot be sub-classed.
  • Singleton can hide dependencies

Factory Design Pattern here

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