Question

Some coders suggest that the Singleton can be an “Anti-Pattern” – that is to say you can actually detract from software by using it. Evaluate the Singleton pattern and assess how it can detract from your software:

Answer 1

// Java program implementing Singleton class
// with getInstance() method
class Singleton
{
   // static variable single_instance of type Singleton
   private static Singleton single_instance = null;

   // variable of type String
   public String s;

   // private constructor restricted to this class itself
   private Singleton()
   {
       s = "Hello I am a string part of Singleton class";
   }

   // static method to create instance of Singleton class
   public static Singleton getInstance()
   {
       if (single_instance == null)
           single_instance = new Singleton();

       return single_instance;
   }
}

// Driver Class
class Main
{
   public static void main(String args[])
   {
       // instantiating Singleton class with variable x
       Singleton x = Singleton.getInstance();

       // instantiating Singleton class with variable y
       Singleton y = Singleton.getInstance();

       // instantiating Singleton class with variable z
       Singleton z = Singleton.getInstance();

       // changing variable of instance x
       x.s = (x.s).toUpperCase();

       System.out.println("String from x is " + x.s);
       System.out.println("String from y is " + y.s);
       System.out.println("String from z is " + z.s);
       System.out.println("\n");

       // changing variable of instance z
       z.s = (z.s).toLowerCase();

       System.out.println("String from x is " + x.s);
       System.out.println("String from y is " + y.s);
       System.out.println("String from z is " + z.s);
   }
}