Real'sHowTo AddThis Feed Button
Custom Search

Check the class versionTag(s): Environment

The first 4 bytes are a magic number, 0xCAFEBABe, to identify a valid class file then the next 2 bytes identify the class format version (major and minor).

Possible major/minor 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

public class ClassVersionChecker {
    public static void main(String[] args) throws IOException {
        for (int i = 0; i < args.length; i++)

    private static void checkClassVersion(String filename)
        throws IOException
        DataInputStream in = new DataInputStream
         (new FileInputStream(filename));

        int magic = in.readInt();
        if(magic != 0xcafebabe) {
          System.out.println(filename + " is not a valid class!");;
        int minor = in.readUnsignedShort();
        int major = in.readUnsignedShort();
        System.out.println(filename + ": " + major + " . " + minor);
> java ClassVersionChecker ClassVersionChecker.class
ClassVersionChecker.class: 49 . 0

from The Java Virtual Machine Specification

The magic item supplies the magic number identifying the class file format; it has the value 0xCAFEBABE.

minor_version, major_version
The values of the minor_version and major_version items are the minor and major version numbers of this class file.Together, a major and a minor version number determine the version of the class file format. If a class file has major version number M and minor version number m, we denote the version of its class file format as M.m. Thus, class file format versions may be ordered lexicographically, for example, 1.5 < 2.0 < 2.1.

A Java virtual machine implementation can support a class file format of version v if and only if v lies in some contiguous range Mi.0 v Mj.m. Only Sun can specify what range of versions a Java virtual machine implementation conforming to a certain release level of the Java platform may support.

blog comments powered by Disqus

If you find this article useful, consider making a small donation
to show your support for this Web site and its content.

Written and compiled by Réal Gagnon ©1998-2014
[ home ]