how to check the version of jar file?

I am currently working on a J2ME polish application, just enhancing it. I am finding difficulties to get the exact version of the jar file. Is there any way to find the version of the jar file for the imports done in the class? I mean if you have some thing, import x.y.z; can we know the version of the jar x.y package belongs to?

Decompress the JAR file and look for the manifest file (META-INF\MANIFEST.MF). The manifest file of JAR file might contain a version number (but not always a version is specified).

You need to unzip it and check its META-INF/MANIFEST.MF file, e.g.

unzip -p file.jar | head

or more specific:

unzip -p file.jar META-INF/MANIFEST.MF

Just to expand on the answers above, inside the META-INF/MANIFEST.MF file in the JAR, you will likely see a line: Manifest-Version: 1.0 ← This is NOT the jar versions number!

You need to look for Implementation-Version which, if present, is a free-text string so entirely up to the JAR's author as to what you'll find in there. See also Oracle docs and Package Version specificaion