code: public void setDeviceId(String deviceId) throws CouldNotPersistException {
          this.deviceId = deviceId;
          if (deviceId != null && path != null) {
              persistDeviceId();
          }
      }
docs: Sets the current device id that the iobeam client is associated with.
  
  @param deviceId Device id to be associated with the iobeam client.
  @throws CouldNotPersistException Thrown if there are problems saving the device id to disk.