Use of Private Constructor

Three uses of private constructor:

1. to prevent instantiation outside of the object, in the following cases:
• singleton
• factory method
• static-methods-only (utility) class
• constants-only class
2. to prevent sublcassing (extending). If you make only a private constructor, no class can extend your class, because it can't call the super() constructor. This is some kind of a synonym for final
3. overloaded constructors - as a result of overloading methods and constructors, some may be private and some public. Especially in case when there is a non-public class that you use in your constructors, you may create a public constructor that creates an instance of that class and then passes it to a private constructor.

Original Link: http://stackoverflow.com/questions/2816123/can-a-constructor-in-java-be-private