midioutdevice.java

java编程的一些Applets例子。值得深入研究一下。

/*	MidiOutDevice.java

	A Java class to handle MIDI output.
*/

package midi;

/**
    MIDI Out interface.
    Defines a consumer of MIDI messages.
 */
interface MidiOut {

	/** Consume a standard short (i.e., non-SysEx) MIDI message */
    public abstract void Out(int message) throws MidiException;
	
	/** Consume a long (i.e., SysEx) MIDI message */
	public abstract void SysExOut(byte buf[], int buflen) throws MidiException;
}



/**
	Handle MIDI output.
*/
public class MidiOutDevice extends MidiDevice implements MidiOut {

    static boolean interfaceLoaded = false;
    static {
        /* try to load the DLL containing the MIDI interface */
        try {
            System.loadLibrary("javamidi");
            interfaceLoaded = true;
        } catch (UnsatisfiedLinkError e) {
            String errmsg = "javamidi.dll not found";
            System.err.println(errmsg);
        }
    }

	/** return the number of installed devices */	
	public static int GetNumDevices() {
		if (interfaceLoaded) {
		    return MidiOutGetNumDevs();
	    } else {
            return -1;
        }
	}

	/*------------- Native Methods -------------*/
	
	/** query the system regarding the number of MIDI output devices */	
	protected static native int MidiOutGetNumDevs();

	/* The following native methods return MMSYSERR_* or MIDIERR_* return codes */
	
	/** open the device; if successful, the instance variable deviceHandle will contain
	    a valid handle */	
	protected native int MidiOutOpen();

	/** reset the device to its default state */
	protected native int MidiOutReset();

	/** close the device */
	protected native int MidiOutClose();

	/** send a non-sysex MIDI message to the device */
	protected native int MidiOutShortMsg(int message);

	/*--------- End of Native Methods ----------*/

	/** Default constructor: open device 0 */
	public MidiOutDevice() throws MidiException {
		this(0);
	}

	/** General constructor: open a particular device */
	public MidiOutDevice(int id) throws MidiException {
		super(id);
	}

	/** Open the device for midi out. */
	public void Open() throws MidiException {
		// only try to open if it is not already open	
 		if (deviceHandle != 0) {
			return;
		}

		// if an attempt to open more than then max number of devices
		// return bad ID error
		if ((MidiOutGetNumDevs() <= deviceId) && (deviceId != MIDI_MAPPER)) {
			throw new MidiBadDeviceException();
    	}
    
		// attempt to open the device
		int rc = MidiOutOpen();

		// if there is an error opening midi out, throw an exception
		if (rc != MMSYSERR_NOERROR) {
			// eventually switch on error code
			throw new MidiException(rc);
		}
	}


	/**
	 * Reset the MIDI out device.  This would also be the logical place to turn
	 * notes off if we add note tracking.
	 */
    public void Reset() {
	    if (interfaceLoaded) {
		    MidiOutReset();
        }
    }


	/**
	 * Close the midi device.
	 */
	public synchronized void Close() throws MidiException {

		if (deviceHandle == 0) {	// not open; nothing to do
			return;
		}
	
		// reset and close midi out
	    Reset();
		int rc = MidiOutClose();

		if (rc == MMSYSERR_NOERROR) {
			deviceHandle = 0;
		} else {
			throw new MidiException(rc);
		}
	}

	/**
	 * Output a midi event
	 */
	
	public synchronized void Out(int message) throws MidiException  {

		if (deviceHandle == 0) {
			throw new MidiDeviceNotOpenException();
		}

		if ((message & 0xF0) == MidiSysEx) {
			throw new MidiException("SysEx messages not supported in this version");
		}

		int rc = MidiOutShortMsg(message);

		if (rc != MMSYSERR_NOERROR) {
			throw new MidiException(rc);
		}
	}

	/** Output a SysEx message */
	public void SysExOut(byte buf[], int buflen) throws MidiException {
		throw new MidiException("SysExOut not implemented yet");
	}
}