I don&#39;t understand what a bluetooth UUID denotes. Do UUIDs denote protocols (e.g. [RFCOMM][1])? If so, why do the `createRfcommSocketToServiceRecord()` methods require UUIDs, when they specify rfcomm right in their names? Why does the BluetoothChat sample code have a seemingly arbitrary, hardcoded UUID?

My question arises because, as per [this question][2], I&#39;m getting a null pointer exception when devices running 4.0.4 try to connect (to an external, non-android device) using reflection. However, the solution to that question doesn&#39;t work for me. `UUID muuid = device.getUuids()[0].getUuid();` raises an exception. 

**Edit**: I&#39;ve solved that problem by hardcoding the UUID for Serial port service as per [this answer][3] (using `UUID.fromString(&quot;00001101-0000-1000-8000-00805f9b34fb&quot;);`).

I&#39;m further puzzled by why I need to supply a UUID to create an unsecured rfcomm socket using `createInsecureRfcommSocketToServiceRecord(),` but not using the reflection method. 

Can anyone straighten me out?


  [1]: http://www.bluecove.org/bluecove/apidocs/javax/bluetooth/UUID.html
  [2]: https://stackoverflow.com/questions/12485785/nullptr-exception-on-socket-connect-galaxy-tab-2-running-android-4-04
  [3]: https://stackoverflow.com/a/11622794/1286571

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Android: How do bluetooth UUIDs work?