How do I turn a folder into a .jar file? I currently have modified a program that is a .jar file. I had unarchived it and turned the .jar file into a folder so that I could edit it. Now all I need to do is change the folder back into a .jar file so that it is not accessible like a folder. How would I do this?
Jar files are almost zip files in most cases, but I would use the jar cf command for best results. 

http://docs.oracle.com/javase/tutorial/deployment/jar/build.html

You could just use OS X compression and then rename the zip file as .jar - but then you might not have a correct manifest file. It's hard to tell without the exact files in hand.