SingleTon

Singleton:

Ensure a class has only one instance, and provide a global point of access to it.

    public class Singleton
    {
        private static Singleton uniqueInstance;
        //other useful instance variables here

        private Singleton()
        {

        }

        public static Singleton getInstance()
        {
            if (uniqueInstance == null)
            {
                uniqueInstance = new Singleton();
            }
            return uniqueInstance;
        }
        //other useful methods here
    }




Where it can be used?
Printer 
For logging
Holding Registry entry in single object.