Using Eclipse I'm trying to edit an old java applet all I have is a .jar, but I can see the files not being able to edit.... the source code is incomplete, so I wanted to edit it and fix it... anyone knows what can I do?
P.S. I just want to modify and fix the program in that jar.
Well first of all, applets are considered obsolete. (In case you didn't know). The files you are trying to see/edit are inside the .jar. So, for me, the easiest way to access the content of a .jar is just changing the extension from .jar to .zip, after that you can access as it was a regular folder and modify whatever you want there. After done, just change the extension to .jar ... Since .jar is like a "package", modifying code while still inside the .jar is not possible/recommended.
Edit: After being able to see the files, you might need a decompiler (as it was mentioned by Jason Braucht in his comment). Check this out:
http://www.javadecompilers.com/
it is an online tool and lets you decompile .class files ...