Suitable Design Pattern for a Simple Chat Application

Question

I am designing a simple chat application (just for the kick of it). I have been wondering of a simple design for that chat application. To give you overview.. here are the r

Answer 1

Just looking at the User object, why does equality depend on id and nickname ? That seems a little counter intuitive to me. I would expect if you have an id, then that is the identification of the object, and hence what you'd use in an equality condition.

I see also that you have a setter for the user id. So do you really want to change user id ? I see that you can change the nickname, which makes sense. But I would expect the id to remain constant.

Note also that since you're overriding equals(), you should also override hashCode().

Now, if hashCode() and equals() rely on immutable fields (e.g. the id), then the results of hashCode() won't change, and if you put a User in a hashed collection (e.g. HashMap) then you're not going to lose it later (which is very confusing)!

Finally (!) I would protect the constructor and setters against null nicknames (make them throw IllegalArgumentExceptions) and then code like equals() doesn't have to worry about a null nickname (unless 'null' has a meaning for the nickname). I would do the same for id, since you have this as a Long (object). But couldn't this be a primitive long ?