Can we put a private constructor in my public class if yes then give the example ?

You want to see private constructors in the C# language and how they can be used to ensure higher-quality code bases on complex projects. Private constructors eliminate the ability of external code in the project to instantiate the class directly, forcing the class to provide a controlled and unified access pattern, as through a singleton.

This C# example program uses a private constructor. Private constructors are needed by singletons.

If you are trying to create the instance of the class Sample

Sample sample = new Sample();  //It throws error.

But if you have static properties then you are eligible to access those properties. Because it can be accessed without creating the instanced.

For more info,

http://msdn.microsoft.com/en-us/library/kcfb85a6(v=vs.80).aspx