Issues when running multiple apps on same JRE?

Question

I've created an application that launches other Java applications, all running on the same JRE. I've noticed that this results in significant memory savings (60% or more). Performance doesn't seem to be measurably affected, but I've never run more than 4 applications at the same time on the same JRE.
Does anyone know of any performance issues in situations like this? JRE limitations? Any information would be appreciated.

Answer 1

"It's just not obvious from the 1.3 API docs that the classLoader is what's responsible for associating a set of classes with a set of threads."
No, that's not what I was implying. The default classloader caches the definition of previously loaded classes (ie, bytecode, static variables). By default, there is no way to unload a class. Static variables will also retain their values -- which could confuse an application that is run multiple times.
This is the suggested implementation defined in the JVM spec:
http://java.sun.com/docs/books/vmspec/html/ConstantPool.doc.html
Basically, if a class has already been loaded, it returns it. You can write your own custom classload to prevent this (as the link you found suggests) or use multiple classloaders.
Imagine what happens when you write an application and then recompile a class WHILE running your application. Will the next instance of that class be updated? The answer depends on whether your classloader will reload the class from disk, or use a cached instance in memory (as the default one does).