I have searching in search Engine regarding convert dex file to jar file but I got failure to find dex2jar file in code.Google.com
I have getting basic idea from here.>
extract the dex2jar-0.0.9.8.zip and in your terminal go to the dex2jar-0.0.9.8 folder and run the delow command
$d2j-dex2jar.sh -f -o test_apk-debug.jar ./Desktop/YourApk.apk
//now you can see the jar file. if you open the jar you can fine the class files under you package name.