Singleton design pattern we can implement using Static key 
word that means only one instance.All the instances are 
coming from the same memory location.

We Can Achieve Singleton Design Pattern By restricting Other
Class To Make Object of the class By Using Constructor
instead we can Use A Static Method to get hold of the
Instance of the class , And By making our Constructor
private we can Restrict other classes to make Instance of
the Class , So that All other Classes use the same static
method to make only one  instance of the  class.