Private constructor

Question

Hi What is private constructor in vb.net ? When we use it ?

Vulpes · Answer

As the name suggests a private constructor is a constructor which is declared as 'private' and so is only accessible from within the class itself. It is used in the following scenarios: 1. If you want to prevent a class from being instantiated (because it only contains shared members) you can introduce a private constructor which does nothing. You need to include such a constructor otherwise the system will by default provide a default public constructor which you don't want. However rather than using a class with a private constructor in this scenario you can use a module to achieve much the same result. 2. If you want to control the number of instances being created you can only allow instantiation via a shared 'Create' method which calls a private constructor internally. This approach is used for creating singletons. 3. If you're using the factory method pattern (see http://en.wikipedia.org/wiki/Factory_method_pattern ) you can force clients to use the shared factory methods by only having a private constructor.