How to find out class name

Question

Hi folks,
Can anybody help me, I got stuck on this problem.
I need to find out the className of the class, which is specified
by ordinary filename.
In other words:
User gives me filename (something.class) and I need to find out
classname (I just need to create an instance of this class)
Thanks a lot.
sgtPepper

Answer 1

This will read the class name from a class file.
* @author Ian Schneider
public class JavaClassName {
    public static void main(String[] args) throws Exception {
        DataInputStream din = new DataInputStream(new FileInputStream(args[0]));
        int cafebabe = din.readInt();
        if (cafebabe != 0xcafebabe)
            throw new Exception("Not class file");
        din.skip(4);
        int cnt = din.readShort() - 1;
        Object[] info = new Object[cnt];
        for (int i = 0; i < cnt; i++) {
            int b = din.readByte();
            switch (b) {
                case 1:
                    info[i] = din.readUTF(); break;
                case 3: case 4: case 9: case 10: case 11: case 12:
                    din.skip(4); break;
                case 5: case 6:
                    i++;
                    din.skip(8); break;
                case 7: case 8:
                    info[i] = Short.valueOf(din.readShort()); break;
                default:
                    assert false;
        din.skip(2);
        int off = din.readShort();
        Number ptr = (Number) info[off - 1];
        System.out.println(info[ptr.intValue() - 1]);
        din.close();
}