Re: Newbie question - Final classes

[cujo@xxxxxxxxxx]

Fred's right.  As I understand it, the optimization is basically being able
to make the calls inline.  Java uses dynamic lookup for all method calls
(very flexible but somewhat slow).  Final methods don't require dynamic
lookup because there can be no overriding methods.  This is basically the
opposite of C++ which uses static method lookup unless you use the virtual
keyword.

Another reason for the final keyword should become more obvious if you look
at a more complex development scenario.  If you are writing the object
heirarchy yourself, you migh very well want to be able to extend anything
anywhere.  However, if *I* write the object hierarchy that you build on top
of, I might not want you to be able to change the way certain things work
for various reasons (security, object integrity, etc).

Regards,

Richard D. Dettinger
AS/400 Java Data Access Team

"TRUE! nervous, very, very dreadfully nervous I had been and am; but why
WILL you say that I am mad?
The disease had sharpened my senses, not destroyed, not dulled them. "

- Edgar Allan Poe
"The Tell-Tale Heart"




Fred Kulack/Rochester/IBM@IBMUS@midrange.com on 11/06/2000 09:35:15 AM

Please respond to JAVA400-L@midrange.com

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To:   JAVA400-L@midrange.com
cc:
Subject:  Re: Newbie question - Final classes




> Would you really want a programmer to sub-class this class ? probably not
!

Uh...
Its perfectly reasonable to _WANT_ to sub-class string.


HOWEVER....
My understanding of final is...
Using final classes is really related to optimizations.
Similar to final objects, the JVM, various JITs can do some good
optimizations if they know for sure that an instance of String is
really ONLY a string, and not some derived class.

I.e. toString() always calls String.toString() and NEVER
StringSubClass.toString().
Strings are primitive enough types and used frequently enough
that these optimizations are probably important.



"Do you believe that my being stronger or faster has anything
 to do with my muscles in this place?" ... "Free your mind."
Laurence Fishburne as Morpheus in 'The Matrix'.

Fred A. Kulack  -  AS/400e  Java and Java DB2 access, Jdbc, JTA, etc...
IBM in Rochester, MN  (Phone: 507.253.5982   T/L 553-5982)
mailto:kulack@us.ibm.com   Personal: mailto:kulack@bresnanlink.net
AOL Instant Messenger: Home:FKulack  Work:FKulackWrk



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