Re: Newbie question - Final classes

>>Please excuse these basic questions but I'm still grappling java after
far
>>too many years in RPG. The question is: Why would you not want a class to
be
>>sub-classed. Can anyone give me a simple example? Or am I
misunderstanding
>>the use of final.

>Alistair
>     as an example, the String class is defined as final...
>Would you really want a programmer to sub-class this class ? probably not
!

>Mike

String is a great example of one of the reasons for final classes.  Because
the String class is final, the compiler can make some assumptions about it,
and that leads to some significant performance benefits.  If String was not
a final class, then the compiler could not make any assumptions, since
subclasses could conceivably change the behavior of even the simplest
methods (such as... equals()!).  But IMHO there's another reason you might
want to make a class final: security.  For example, if one of your classes
deals with security, it wouldn't be difficult for a programmer to subclass
it and override some of the secure routines.  Of course, using final is not
the end-all and be-all for security; a user could conceivably put a
non-secure version of the same class in their own jar file earlier in the
classpath; that's one more argument for having your own class loader (there
are other reasons, but security in particular is a very good one).

Joe

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