It seems to me that you would just use a classLoader to load the class
and execute the main method.

You can, but they wont be entirely independent.

 o Create a new ClassLoader with the URLs of the program code. null as
the parent class loader will stop the libraries you are using interfere
with the libraries it is using.

   ClassLoader loader = URLClassLoader.newInstance(new URL[] { url },
null);

http://download.java.net/jdk6/docs/api/java/net/URLClassLoader.html#newInstance(
java.net.URL[],
java.lang.ClassLoader)

 o Find you the applications main class (I guess you could look up
Main-Class in its manifest).

   Class<?> mainClass = Class.forName(mainName, false, loader);

http://download.java.net/jdk6/docs/api/java/lang/Class.html#forName(java.lang.String,
boolean, java.lang.ClassLoader)

 o Find the main method.

   Method mainMethod = mainClass.getMethod("main", String[].class);

http://download.java.net/jdk6/docs/api/java/lang/Class.html#getMethod(java.lang.
String,
java.lang.Class...)

 o Invoke main method. Note how varargs doesn't work too well.

   mainMethod.invoke(null, new Object[] { new String[] { /* args */ }});

http://download.java.net/jdk6/docs/api/java/lang/reflect/Method.html#invoke(java
.lang.Object,
java.lang.Object...)

(Disclaimer: I've not tested or even compiled this code. However, I have
written similar stuff before).

You will be sharing the JVM, but for AWT/Swing applications you wont be
able to do the separate AppContext thing. You can create a new
ThreadGroup for the application if you so wish.

It's not *that* bad is it?

Tom Hawtin