what is "receiver-device-id"

while i was reading the documentation in the messaging section i had problem understanding what is it and how to retrieve it

DeliveryOptions deliveryOptions = new DeliveryOptions();
deliveryOptions.addPushSinglecast( receiver-device-id );

thanks .

It is a registration ID of the device which you send message to. The registration ID is received as a result of the registerDevice API call.

Regards,
Mark