A MidiDevice can be a transmitter or a receiver of MIDI events, or both. Therefore, it can provide Transmitter or Receiver instances (or both). Typically, MIDI IN ports provide transmitters, MIDI OUT ports and synthesizers provide receivers. A Sequencer typically provides transmitters for playback and receivers for recording.

A MidiDevice can be opened and closed explicitly as well as implicitly. Explicit opening is accomplished by calling open(), explicit closing is done by calling close() on the MidiDevice instance. If an application opens a MidiDevice explicitly, it has to close it explicitly to free system resources and enable the application to exit cleanly. Implicit opening is done by calling MidiSystem.getReceiver() and MidiSystem.getTransmitter(). The MidiDevice used by MidiSystem.getReceiver and MidiSystem.getTransmitter is implementation-dependent unless the properties javax.sound.midi.Receiver and javax.sound.midi.Transmitter are used (see the description of properties to select default providers in MidiSystem). A MidiDevice that was opened implicitly, is closed implicitly by closing the Receiver or Transmitter that resulted in opening it. If more than one implicitly opening Receiver or Transmitter were obtained by the application, the device is closed after the last Receiver or Transmitter has been closed. On the other hand, calling getReceiver or getTransmitter on the device instance directly does not open the device implicitly. Closing these Transmitters and Receivers does not close the device implicitly. To use a device with Receivers or Transmitters obtained this way, the device has to be opened and closed explicitly.

If implicit and explicit opening and closing are mixed on the same MidiDevice instance, the following rules apply:

• After an explicit open (either before or after implicit opens), the device will not be closed by implicit closing. The only way to close an explicitly opened device is an explicit close.
• An explicit close always closes the device, even if it also has been opened implicitly. A subsequent implicit close has no further effect.

 MidiDevice device = ...;
 if (!(device instanceof Sequencer) && !(device instanceof Synthesizer)) {
   // we're now sure that device represents a MIDI port
   // ...
 }
 

A MidiDevice includes a MidiDevice.Info object to provide manufacturer information and so on.