You shouldn't be opening jar files with an editor. If you need the files inside you can either use the jar program given by the jdk in order to get the file, or something like winrar which will give you access as well.
A text editor will not help you out as a jar is a compressed archive as well as an executable format for java files.
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"To iterate is human, to recurse divine." -L. Peter Deutsch
You can't edit them. As I said all you can do is extract them, and hope that the .java files are in there. If they aren't then you have .class files that you shouldn't be editing anyways.
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"To iterate is human, to recurse divine." -L. Peter Deutsch
.jar files are archive files. What I always do (might not work for you) is rename the jar file to a .zip file and extract it. Might not work for you, but for me it does.