jar files

I made/am making a project, and I made a jar file for it. The program executes perfectly when it is in the directory it was created in. When I move it elsewhere, the application does not appear. How can I fix this?

If you have multiple classes, make sure you pack all the .class files required into the jar file. The alternative is to copy the .class files along with the jar file. There may be other API's that your project is using (such as JExcel, Java3D, Java Sound, etc.) that you'll need to make sure your jar file knows where they are.

All the files are in the JAR, how do I make it know where the API is if it needs it?