[Jython-dev] jreload--it IS possible to reload a class in the same classloader

[Updike, C. <Cla...@jh...>]

regarding http://www.jython.org/docs/jreload.html and the statement:

"Why there is no support for reloading a single class? Java classes are
loaded through class-loaders, actually there is no support in java to
redefine an already loaded class through its class-loader."

I don't mean to split hairs here, but it IS actually possible to redefine an
already-loaded class in the same classloader as long as you use Class
methods to load it.  i.e. 
use:

Class redefineable = Class.forName("MyRedefinealbeClass");
redefineable.newInstance();

// Assume the previous version of MyRedefineableClass.class was modified
// Reload the new one...
redefineable  = null;
System.gc();
Class redefineable = Class.forName("MyRedefineableClass");
redefineable.newInstance();

Instead of:

MyUNRedefinableClass unRedefineable = new MyUNRedefineableClass();
murdc = null;

// does NOT pick up any changes to MyRedefineableClass.class
unRedefineable = new MyUNRedefineableClass(); 


This functionality is described in the following article,
http://www.sys-con.com/java/articleprint.cfm?id=307 

I don't know if this adds any new possibilities for jreload or not (or if
I'm wrong), but thought it worth pointing out anyway.  Note that the article
makes a call to System.gc() to "force" the classloader to dump the current
version but I don't believe System.gc() guarantees that this will happen.

-Clark