Singleton Object Creation

Steps to Create          

      Default constructor is made private [It prevents the direct instantiation of the object by others (Other Classes).

      A static modifier is applied to the instance method that returns the single object [can be accessed without creating an object]


      synchronization is only needed during initialization on singleton instance[To prevent creating another instance of Singleton]
 

Example

package com.javalearning.crazy;

public class SingletonObject {

      private static SingletonObject singletonObj = null;

      private SingletonObject()

      {   

      }

      public static synchronized SingletonObject getInstance() {

            if (singletonObj == null) {

                  singletonObj = new SingletonObject();

            }

            return singletonObj;

      }

      public static void main(String[] args) {

            SingletonObject singletonObj = null, singletonObj1 =null;

            singletonObj = SingletonObject.getInstance();

            singletonObj1 = SingletonObject.getInstance();

            System.out.println(singletonObj+"="+singletonObj1);       

      }

}

Benefits

Singletons can be used to create a Connection Pool.


lazy loading - instance is created only when client calls getInstance() [method is loaded before instance created]

Drawbacks

Need to be cautious in multi threaded environment.

We can still be able to create a copy of the Object by cloning