how to find the java class version

step1: Go to the command prompt.

Step2: type the command
           javap -verbose classname(class name for want to inspect)
          EX: javap -verbose UserAction

In the above image shows the version of JVM as 51 which is JDK 1.7.

Here is the List of JVM versions value:

major  minor  Java platform version 

----------------------------------
45       3           1.0
45       3           1.1
46       0           1.2
47       0           1.3
48       0           1.4
49       0           1.5
50       0           1.6

51       0           1.7