What is the use of private constructor in a class

Question

what is the use of private constructor in a class

Alan · Answer

A private constructor prevents a class from being publicly instantiated. In C# 1.0/1.1 you might want to do this if your class consists of nothing else but static members. However following the introduction of 'static classes' this is no longer necessary in C# 2.0. It has never been necessary in VB.Net which has the 'Module' to perform a similar function to the static class. You might also want to use a private constructor if you only want to allow one object of a class to be instantiated (the so called 'singleton' pattern). You can then allow the single object to be created or accessed via a public static method or property of the class. The first time it is called this method/ property would create the singleton by calling the private constructor internally.