Question

Why do we have to override init() method in Servlets while we can do the initialization in the constructor and have web container call the constructor passing ServletConfig reference to servlet while calling constructor?

Ofcourse container has to use reflection for this but container has to use reflection anyway to call a simple no-arg constructor

Answer 1

Since a constructor can not be part of an interface, it can not be “formally” specified within the Servlet API, unlike normal methods. Moreover, since Java has no destructors, a destroy method is needed anyway, so it defining the corresponding init method makes the API more consistent and easier to use.

Using reflection to detect/verify constructor parameters would just unnecessarily complicate things, and I don’t see any added value.