Question

I know this is a very common question, but I tried googling and got no helpful result.
I’m trying to make a jar out of my “Main.class” file (made in NetBeans, but I’m not trying to make the jar with it)

I ran this command:

D:\NetBeans\trovanum3\build\classes\trovanum3>jar cf trovanum.jar *.class

And a .jar file spawned in that folder. I thought that would’ve worked, but it won’t run.

I tried opening the jar file with an archive opener and inside it are the “Main.class” file and a “META-INF” folder containing a file named “MANIFEST.MF”
The file contains this:

Manifest-Version: 1.0
Created-By: 1.6.0_22 (Sun Microsystems Inc.)

What could be the problem?

Answer 1

You can use the -e option of jar to specify the entry point, i.e. the main class. For example:

D:\NetBeans\trovanum3\build\classes> jar cfe trovanum.jar trovanum3.Main trovanum3\*.class

Saves fiddling with the manifest if that’s all you need in there. Note the working directory is one up from that quoted in your question. Otherwise the Main class is created at the top-level in the jar, rather than in a directory that reflects the package in which it should reside. jar -tvf should then show something like this:

  0 Thu Oct 21 22:34:30 BST 2010 META-INF/
 80 Thu Oct 21 22:34:30 BST 2010 META-INF/MANIFEST.MF
488 Thu Oct 21 22:18:24 BST 2010 trovanum3/Main.class

-e

Sets entrypoint as the application
entry point for stand-alone
applications bundled into executable
jar file. The use of this option
creates or overrides the Main-Class
attribute value in the manifest file.
This option can be used during
creation of jar file or while updating
the jar file. This option specifies
the application entry point without
editing or creating the manifest file.