If you often launch JAR (or JAD) files, and you need to executer these files in various environments, then Hitonic JAR-Starter is what you are looking for.
Quick example, you have some Java environments on your PC: Java 2SE JDK 1.4.0, Java 2SE JDK 1.5.0, Sun WTK 1.0.4, Sun SDK 3.0, Nokia S60 3rd FP2 SDK. What happens if you click on a JAR-file?
That's right. You launch the file in the last installed environment.
Hitonic JAR-Starter allows you select the environment on the fly.
Hitonic JAR-Starter launches JAR and JAD files in various J2SE (JDK/JRE) and J2ME (emulators) environments.