Class File Information

[Saurav Chetia]

If I have a java class file and I want to know about it's version(major and minor) how to obtain those values ?
I used com.ibm.toad.cfparse package. Using the ClassFile class I tried to get the major and minor versions but I get the default values of MajorVersion : 45 , and MinorVersion : 3.
I used the ClassFile constructor with InputStream argument.
Can someone tell me what am I am I missing here ?
Or else please suggest some other technique to get those information.
Thanks

[Michael Morris]

Hi Saurav,
See if this doesn't work:

import java.io.*;
public class ClassFileHeader {
    public static void main(String[] args) throws IOException {
        if (args.length != 1) {
            System.out.println("Usage: java ClassFileHeader file.class");
            System.exit(1);
        }
        FileInputStream in = new FileInputStream(args[0]);
        int[] magic = new int[4];
        int[] minor = new int[2];
        int[] major = new int[2];
        /*
         * The first four bytes are the magic number which should be CAFEBABE
         * for a class file.
         */
        magic[0] = in.read();
        magic[1] = in.read();
        magic[2] = in.read();
        magic[3] = in.read();
        int magicNumber = magic[0] << 24 | magic[1] << 16 |
                          magic[2] <<  8 | magic[3];
        /*
         * The next two bytes are the minor version.
         */
        minor[0] = in.read();
        minor[1] = in.read();
        int minorVersion = minor[0] << 8 | minor[1];
        /*
         * The next two bytes are the major version.
         */
        major[0] =  in.read();
        major[1] =  in.read();
        int majorVersion = major[0] << 8 | major[1];
        in.close();
        StringBuffer sb = new StringBuffer();
        sb.append("Magic: ");
        sb.append(Integer.toHexString(magicNumber).toUpperCase());
        sb.append(" Version: ");
        sb.append(majorVersion);
        sb.append(".");
        sb.append(minorVersion);
        System.out.println(sb.toString());
    }
}

Michael Morris

[Saurav Chetia]

Thanks Michael!
That was a simple method to obtain information from a class file.
I just had doubt related with JVM implementation of JDK versions and the Class file format supported. Got the information from the Sun's JVM Specification.
Thanks again
-Saurav