A class which must create only one object (ie. One instance) irrespective of any number of object creations based on that class.
Steps to develop single ton class:-
1.Create a Private construcor, so that outside class can not access this constructor. And declare a private static reference of same class
2.Write a public Factory method which creates an object. Assign this object to private static Reference and return the object
private static SingleTon st=null;
public static SingleTon stfactory()
if(st==null) st=new SingleTon();
For complete Example of Singleton design pattern click here