Making a JAR file runnable

Aside from attributes, you can put a few special values in the manifest file. One of these, Main-Class, allows you to specify the class containing the primary main() method for an application contained in the JAR:

 Main-Class: com.oreilly.Game  

If you add this to your JAR file manifest (using the m option described earlier), you can run the application directly from the JAR:

 % java -jar spaceblaster.jar  

More importantly, under Mac OS X, Windows, and other GUI environments, you can simply double-click on the JAR file to launch the application. The interpreter looks for the Main-Class value in the manifest, then loads the designated class as the application’s startup class.