Class.forName reasonably efficient

[Roedy Green]

I did some timing of class.forName. It turns out it is reasonably
quick

Class.forName eagerly loads the class if it not already loaded. Inside
the JVM there is a HashMap of all the classes that have been
previously loaded. So Class. forName takes under a millisecond if the
class you have want is already loaded, If not, it might take 15
milliseconds or so to load it. You pay this time penalty only the
first time you use the class. Class. forName is still slower than hard
coding the name of the class into your code. With hard coding, you
avoid repeated HashMap lookups.

 

[mgungora]

Does Class.forName re-load a class if the timestamp on it is newer?
Probably not... Is there a way to force it to do a re-load?

 

[Roedy Green]

Does Class.forName re-load a class if the timestamp on it is newer?
Probably not... Is there a way to force it to do a re-load?

nope. It won't even look. Once you load a class it stays loaded. the
only way to do that is with a ClassLoader. Then to the jvm the new
class is a brand new class.

At some point I should write a demo to replace a class on the fly and
upgrade old to new objects.

 

[opalpa]

In most applications Roedy is completely correct -- a custom class
loader needs be created. The exception I know of is that some servlet
servers have reloading as a configuration option. One example is
com.iplanet.ias.classloader.IasWebClassLoader

Opalinski
(e-mail address removed)
http://www.geocities.com/opalpaweb/

 

[Dave Glasser]

In most applications Roedy is completely correct -- a custom class
loader needs be created. The exception I know of is that some servlet
servers have reloading as a configuration option. One example is
com.iplanet.ias.classloader.IasWebClassLoader

And it would use a custom classloader. Or more specifically, one other
than the system classloader.


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