hmm, simplest way to launch a Java program from another Java program is to load the classes onto the active classpath, load the main class into a classloader, and then execute the main() method on that class.
No need to use ProcessBuilder to create a new JVM, just make sure you have the jar on your classpath and call SomeClass.main(new String) or something like that :)
Yes. That was the other solution I had in mind too, especially if he wants to interact with the classes in the jar directly.
ProcessBuilder would be more appropriate if the jar is just a "black box" application that happens to be in java, and especially if you want to pipe its sysin or sysout.