Determining Version of JVM used to build class file

The details are given in Thiam Teck’s Blog.

Basically, the command

javap -verbose ClassName

is given and the extensive dump is mined for the major version and minor version of java used. The cited blog gives a table of major/minor pairs that go from 1.0 through 1.6.

Another way (if you have binary dump program) is to look at the first 8 bytes of the .class file as discussed in Real’s How To. For my example file, the first bytes are:

CA FE BA BE 00 03 00 2D

The first four bytes CA FE BA BE are a signature for a .CLASS file, while the next two bytes are the minor version (3) and the major version (2D or 45 base 10). The cited article (and the JVM documentation) will match this up to JVM 1.1 for the example file. Version 1.5 of the JVM runs this class file with no problem.  Real’s How To also gives a sample program for those who have a binary editor.

Update February 2020

Changed my web site server link.