What is the difference between dictionary(Of String, String) and IDictionary(Of String, String)

Question

Can I do anything more or less with IDictionary? How do these two collections differ?

Answer 1

IDictionary is only an interface - a contract which describes what an implementing class must do. Dictionary is a concrete class that implements that interface and hence must provide the methods described in the IDictionary interface.

If you want to create a dictionary you must create a concrete class (i.e. Dictionary), but if all you want to do with that dictionary is methods exposed by the IDictionary interface you can pass the concreate class round as an interface - which reduces the coupling between methods.