Write a program in Java to demonstrate the use of private constructor and also write a method which will count the number of instances created using default constructor only.

 

AIM: Write a program in Java to demonstrate the use of private constructor and also write a method which will count the number of instances created using default constructor only.

 

CODE:

class Singleton{

   static int count=0;

   //private instance Object of same class

  private static Singleton single_instance = null;

   //private constructor

   private Singleton() {

               count++; 

            }

   // Method that creates and returns same class that is Singleton Object.

   static public Singleton createInstance(){

                        if(single_instance==null){

                                    single_instance = new Singleton();

                        }

   return single_instance;   

   } 

   void display(){

                        System.out.println("Count: "+count);

   }

} 

class SingletonMain{    

                        public static void main(String args[]) { 

                                    Singleton s1 = Singleton.createInstance();

                                    Singleton s2 = Singleton.createInstance();

                                    s1.display();

                                    s2.display();   

                        }  

 }

OUTPUT: