how and in which situation we can use Singletone design pattern?

This links demonstrates a real world example of Singleton pattern
http://www.dofactory.com/Patterns/PatternSingleton.aspx[^]
http://softwarekaffee.blogspot.in/2012/02/real-world-example-of-singleton-design.html[^]

Hope this helps

Purpose :
Singletone is generally use for object optimization purpose. A project to develop a software where number of object is an important issue and the software weight is an important issue we use Single tone.
How :
Step 1: Create a class
Example:

class SingletoneExample
{
}

Step 2: Set the constructor as private.
Example:

class SingletoneExample
{
   private SingletoneExample()
  {
  }
}

Step 3: Create class type reference variable.
Example :

class SingletoneExample
{
   private SingletoneExample instance;
   private SingletoneExample()
  {
  }
}

Step 4: Create a method. Set the method type as Class Type.create a object with the reference of class type varible and return it.

class SingletoneExample
{
   private SingletoneExample instance;
   private SingletoneExample()
  {
  }
  public static SingletoneExample getInstance()
  {
    instance=new SingletoneExample();
    return instance;
  }
}

Step 5: From other class you call the singletoneExample class behaviour.
Step 6: The singletoneExample class becomes singletone.