Singleton Pattern Implementation

Singleton Pattern.md

Singleton Pattern

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Singleton Pattern is one of the mostly known and used design pattern among all the GOF design patterns.

Principles of a Singleton Object:

• There exists one and only one instance of this object
• The state of the object is shared across all the threads in the VM
• In most cases data synchronization is done, unless there it is not needed (Not a Must)

In this Gist i would like to share the best possible way of creating a Singleton Object.

public class SampleObject {
    
    private static class SampleObjectSingleton{
        private static final SampleObject instance = new SampleObject();
        public static SampleObject getInstance(){
            return instance;
        }    
    }
    
    /* Private Constructor is a must for any Singleton Object */
    private SampleObject(){}
    
    /* A method to get access to the instance of this Singleton object */
    public static SampleObject getInstance(){
      return SampleObjectSingleton.getInstance();
    }
    
    // More Business methods
}

Benefits of the above format

• The object instance is created only once, as it is created as a static final reference of inner class.
• The object will not be created unless, a getInstance() method on SampleObject is called
• Loading the class will not create an instance, as the inner class will not be instantiated until its used.

I have also discussed several other ways of creating the Singleton objects along with the advantages and disadvantages in my [blog post] (http://www.novicehacks.info/2014/02/singleton-pattern.html) on singleton pattern.

Hope this helps. -- Sharath