Private Constructor

http://www.javapractices.com/topic/TopicAction.do?Id=40

If the programmer does not provide a constructor for a class, then the system will always provide a default, public no-argument constructor. To disable this default constructor, simply add a private no-argument constructor to the class. This private constructor may be empty.

In these cases, the lack of an accessbile constructor says to the caller : "There are no use cases for this class where you need to build an object. You can only use static items. I am preventing you from even trying to build an object of this class."