singleton is a design pattern that focus on object creation. When a class is implemented using singleton, one and only one such instance can be created in a JVM. Usual implementation will be: 1. making constructor private 2. use a public static "getInstance" method to get an instance object 3. use either lazy instantiation or instantiate it statically 4. if lazy instatiation is used, must synchronized "getInstance" method. 5. the singleton object is private static instace field In some cases you may prefer a abstract class with all static methods.