static byte[] DEX_FILE_MAGIC = { 0x64, 0x65, 0x78, 0x0a, 0x30, 0x33, 0x35, 0x00 };

  static boolean isDex(byte[] dexData) {
    if (dexData.length < DEX_FILE_MAGIC.length) return false;
    for (int i = 0; i < DEX_FILE_MAGIC.length; i++)
      if (dexData[i] != DEX_FILE_MAGIC[i])
        return false;
    return true;
  }