Igor Kromin |   Consultant. Coder. Blogger. Tinkerer. Gamer.

It's easy to check the JDK version that a .class file has been compiled with using the javap tool. Simply run something like this...
javap -v MyClass | grep major

That will produce output like this...
major version: 51

Even though I primarily code in Java, I never remember the class version names and their equivalent JDK versions. So instead of looking it up I added this handy function to my Bash ~/.profile file to tell me the JDK version for a .class file...
 Bash ~/.profile function
jversion() {
case $(javap -v $1|grep major|awk '{print $3}') in
echo 'Java 1.2'
echo 'Java 1.3'
echo 'Java 1.4'
echo 'Java 5'
echo 'Java 6'
echo 'Java 7'
echo 'Java 8'
echo 'Java 9'
echo 'Unrecognised Java version'

Using it is simple, simply do this:
jversion MyClass

The output is a little bit more friendly than what javap produces, for example:
Java 8


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