public class ValidateTest
{

    public static void main(String[] args)
    {
        ValidateTest t = new ValidateTest();
        String s = "abcdefghijklmnopqrstuvwxyz12345678987654321";
        byte[] buf = t.getBuffer(s);
        byte[] res = new byte[4];
        t.getChkSum(buf.length, buf, res);
    }

    byte[] getBuffer(String s)
    {
        byte[] buf = s.getBytes();
        int len = buf.length;

        int temp = 0;
        if (len % 4 != 0)
        {
            temp = 4 - len % 4;
        }
        byte[] buf1 = new byte[len + temp];

        System.arraycopy(buf, 0, buf1, 0, len);
        return buf1;
    }

    void getChkSum(int len, byte[] buf, byte[] res)
    {
        for (int i = 0; i < len; i += 4)
        {
            res[0] ^= buf[0 + i];
            res[1] ^= buf[1 + i];
            res[2] ^= buf[2 + i];
            res[3] ^= buf[3 + i];
        }
        res[0] = (byte) ~res[0];
        res[1] = (byte) ~res[1];
        res[2] = (byte) ~res[2];
        res[3] = (byte) ~res[3];
    }
}