To my knowledge a *.jar file uses the same compressing technique as a *.zip file. They are (more or less) interchangable.
The jar program includes a meta-inf directory (with...), which a 'zipper' doesn't.
Using a zipper you need to use the feature to include path information (for packages).
So for java-programs I use jar and very often make the jar file with extension *.zip to look automatically with those nice zip-programs to the content.
(I love this smiley)
Peter