immutable class should be final?

Question

It says in this article that:

Making a class final because it is immutable is a good reason to do so.

I\'m a bit puzzled by thi

Answer 1

Its a good idea to make a class immutable for performance reasons too. Take Integer.valueOf for example. When you call this static method it does not have to return a new Integer instance. It can return a previously created instance safe in the knowledge that when it passed you a reference to that instance last time you didn't modify it (I guess this is also good reasoning from a security reason perspective too).

I agree with the standpoint taken in Effective Java on these matters -that you should either design your classes for extensibility or make them non-extensible. If its your intention to make something extensible perhaps consider an interface or abstract class.

Also, you don't have to make the class final. You can make the constructors private.