public class MACAddress {

   private static final int MAC_LEN = 6;

   private byte[] data;

   public MACAddress(String addr) {
      this(parseMAC(addr));
   }

   public MACAddress(byte[] addr) {
      if (addr.length != MAC_LEN)
         throw new IllegalArgumentException(
            "MAC address has wrong number of bytes: " + addr.length);
      this.data = new byte[MAC_LEN];
      System.arraycopy(addr, 0, data, 0, MAC_LEN);
   }

   public byte[] getAddress() {
      byte[] ret = new byte[MAC_LEN];
      System.arraycopy(data, 0, ret, 0, MAC_LEN);
      return ret;
   }

   /**
    * Parses a MAC address on the format 'XX:XX:XX:XX:XX:XX'.
    */
   private static byte[] parseMAC(String mac) {
      String[] bytes = mac.split(":");
      if (bytes.length != MAC_LEN)
         throw new IllegalArgumentException("Bad MAC address: '" + mac + "'");

      byte[] data = new byte[MAC_LEN];
      for (int i = 0; i < bytes.length; i++) {
         int b = Integer.parseInt(bytes[i], 16);
         if (b < 0 || b > 255)
            throw new IllegalArgumentException("Bad MAC address: '" 
                                               + mac + "'");
         data[i] = (byte)b;
      }

      return data;
   }

   private static StringBuffer appendHexByte(StringBuffer sb, byte b) {
      sb.append(Character.forDigit((b >> 4) & 0x0f, 16));
      sb.append(Character.forDigit(b & 0x0f, 16));
      return sb;
   }

   public String toString() {
      StringBuffer sb = new StringBuffer();
      for (int i = 0; i < MAC_LEN; i++) {
         appendHexByte(sb, data[i]);
         if (i < MAC_LEN-1)
            sb.append(':');
      }
      return sb.toString();
   }

}