Re: [Jscheme-user] defining new classes

[Ken A. <kan...@bb...>]

At 10:00 PM 1/6/2003, david may wrote:
>I found this today, and it seems usefull.
>are there any gotchas to this method oc creating 
>new class in jscheme?

In addition to what Tim said, you need to be a little careful when using multiple class loaders.  Loaders have a parent link and when loading a class they are supposed to ask the parent to load the class first, if it can.
If it can't the loader will try loading it.  Unfortunately, a class loaded by the parent of a class loader can't see a class loaded by the class loader.
I use dynamic class loading, for example the following code will add all the jar files in the lib/ directory to the class path:

(load "using/run.scm")
(load "elf/classpath.scm")
(for-each
 (lambda (u) (.addURL (Import.getClassLoader) (url u)))
 (files* (File. "lib") isJarFile))

I even sometimes smash the system class loader.


I think the right solution is to have your main create at class loader and then run your application through it, as Chiba's tutorial shows.
See build/SchemeLite.java for example.

I'm having a problem with the Bean Scripting Framework related to this and may change how JScheme starts.

BTW, i have a class loader that will let you reload a Java class.  This will let you test a Java class through JScheme and let you recompile it without leaving JScheme.


>Sometimes you want to make a  subclass just to 
>override the paint method. 
>
>the jar file is here..
>http://www.csg.is.titech.ac.jp/~chiba/javassist/
>
>------------ a simple test -----------
>(import "javassist.*")
>(define  pool  (javassist.ClassPool.getDefault))
>(define cc (.makeClass  pool "Silly"))
>(define m  (CtNewMethod.make 
>       "public int silly(int dx) { return 2+dx; }" cc))
>(.addMethod cc m)
>
>(define cloader (Loader. pool))
>(define anewclass  (.loadClass  cloader "Silly"))
>(define ss1 (.newInstance anewclass))
>
>(.silly ss 1)
>
>
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