Why does the String class not have a parameterless constructor?

Question

int and object have a parameterless constructor. Why not string?

Answer 1

int is a value type, and as such it must have a parameterless constructor. There is no consideration that can be made here.

object has no reason to have anything but a parameterless constructor. There is no data to give it. What parameters would you expect it to take? objects constructed with a parameterless constructor also have a purpose; they are used, for example, as objects to lock on. It is however a class, so it doesn't need to have a public parameterless constructor, however since it has no need for parameters, it's a question of whether you want instance of it to be constructed at all; Microsoft chose to make it concrete, rather than abstract.

string is a class, so it isn't required to have a parameterless constructor. The team building it simply never saw a need to have one. One could sensibly use such a constructor to create an empty string, but they choose to expose string.Empty (as well as an empty string literal) as a way of explicitly creating an empty string. Those options have improved clarity over a parameterless constructor.

Another pretty significant advantage of string.Empty and the empty literal string is that they are capable of re-using the same string instance. Since strings are immutable, the only way to observe the difference between two different references to empty strings is through the use of ReferenceEquals (or a lock on the instance). Because there is virtually never a need to go out of your way to have different references to an empty string, removing the parameterless constructor removes the possibility of an equivalent but poorer performing method of constructing an empty string. In the very unlikely event that it is important to construct a new string instance that is an empty string, an empty char array can be passed to the relevant constructor overload, so removing the parameterless constructor doesn't remove any functionality from the end user; it simply forces you to go out of your way to do something really unusual if you want to do something really unusual, which is the sign of good language design.