Where and how can you use a private constructor in Java ??

Question

By making private constructor, we can avoid instantiating class from anywhere outside and by making class final, no other class can extend it. Why is it necessary for Util class to have private constructor and final class ?

Answer 1

Source: http://www.javabeat.net/qna/819-where-and-how-can-you-use-a-private-construct/
Private constructor can be used if you do not want any other class to instanstiate the object , the instantiation is done from a static public method, this method is used when dealing with the factory method pattern when the designer wants only one controller (fatory method ) to create the object.