Midi example from Head First Java

Hi everyone,
I am reading a book called "Head First Java" by Kathy Sierra and Bert Bates. One example piece of code uses a MIDI sequencer to generate a sound.
Unfortunately it doesn't work for me, even if I tried it both on Ubuntu and Windows. When I run it I only hear either a short piano note or a kind of knock.
Changing the arguments should give a different instrument and note, but it always plays the same sound when I execute it.
I don't know anything about sound and MIDI devices, so I don't know how to fix the problem.

I give the code below.
After compiling it I execute the command with different arguments:
java MiniMusicCmdLine 102 30
java MiniMusicCmdLine 80 20
java MiniMusicCmdLine 40 70

They're supposed to produce notes of different pitch, but I always hear the same short knock or sometime a piano note (but always of the same pitch).

I welcome any help at the beginner level.

----------------------

import javax.sound.midi.*;

public class MiniMiniMusicCmdLine {

public static void main(String[] args) {
MiniMiniMusicCmdLine mini = new MiniMiniMusicCmdLine();
if (args.length < 2) {
System.out.println("Don't forget the instrument and note args");
} else {
int instrument = Integer.parseInt(args[0]);
int note = Integer.parseInt(args[1]);
mini.play(instrument,note);
}
} // close main

public void play(int instrument, int note) {
try {
Sequencer player = MidiSystem.getSequencer();
player.open();
Sequence seq = new Sequence(Sequence.PPQ, 4);
Track track = seq.createTrack();

MidiEvent event = null;

ShortMessage first = new ShortMessage();
first.setMessage(192, 1, instrument, 0);
MidiEvent changeInstrument = new MidiEvent(first, 1);
track.add(changeInstrument);

ShortMessage a = new ShortMessage();
a.setMessage(144, 1, note, 100);
MidiEvent noteOn = new MidiEvent(a, 1);
track.add(noteOn);

ShortMessage b = new ShortMessage();
a.setMessage(128, 1, note, 100);
MidiEvent noteOff = new MidiEvent(b, 16);
track.add(noteOff);

player.setSequence(seq);
player.start();
} catch (Exception ex) {ex.printStackTrace();}
} // close play

} // close class

I just copied this into Eclipse and ran it.. I get the same little "knock".

Unfortunately, I don't know very much about the sound API, but I have helped others here before with similar issues.

Do a search here for midi or sound and take a look at some of the examples and fixes.

Pat.

Welcome to the Ranch

I cannot comment because I haven’t got my copy of the book here, but it is worth comparing it very carefully to what is in the book.

Hi both,
Thank you for your reply. The advice to check carefully the code from the book was right: I made a mistake in copying it! In fact line 36 should be "b.setMessage ..." instead of "a.setMessage ...". Now it works fine.
Thank you,
Eubulide

Well done finding that error