BeatBox.java

import java.awt.*;
import javax.swing.*;
import javax.sound.midi.*;
import java.util.*;
import java.awt.event.*;

public class BeatBox {
    JPanel mainPanel;
    ArrayList<JCheckBox> checkboxList;
    Sequencer sequencer;
    Sequence sequence;
    Track track;
    JFrame theFrame;

    String[] instrumentNames = { "Bass Drum", "Closed Hi-Hat", "Open Hi-Hat", "Acoustic Snare", "Crash Cymbal", "Hand Clap", "High Tom", "Hi Bongo", "Maracas", "Whistle", "Low Conga", "Cowbell", "Vibraslap", "Low-mid Tom", "High Agogo", "Open Hi Conga"};
    int[] instruments = {35, 42, 46, 38, 49, 39, 50, 60, 70, 72, 64, 56, 58, 47, 67, 63};

    public static void main(String[] args){
        new BeatBox().buildGUI();
    }

    public void buildGUI() {
        theFrame = new JFrame("Cyber BeatBox");
        theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        BorderLayout layout = new BorderLayout();
        JPanel background = new JPanel(layout);
        background.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));

        checkboxList = new ArrayList<JCheckBox>();
        Box buttonBox = new Box(BoxLayout.Y_AXIS);

        JButton start = new JButton("Start");
        start.addActionListener(new MyStartListener());
        buttonBox.add(start);

        JButton stop = new JButton("Stop");
        stop.addActionListener(new MyStopListener());
        buttonBox.add(stop);

        JButton upTempo = new JButton("Tempo Up");
        upTempo.addActionListener(new MyUpTempoListener());
        buttonBox.add(upTempo);
        
        JButton downTempo = new JButton("Tempo Down");
        downTempo.addActionListener(new MyDownTempoListener());
        buttonBox.add(downTempo);

        Box nameBox = new Box(BoxLayout.Y_AXIS);
        for (int i = 0; i < 16; i++){
            nameBox.add(new Label(instrumentNames[i]));
        }

        background.add(BorderLayout.EAST, buttonBox);
        background.add(BorderLayout.WEST, nameBox);

        theFrame.getContentPane().add(background);

        GridLayout grid = new GridLayout(16, 16);
        grid.setVgap(1);
        grid.setHgap(2);

        mainPanel = new JPanel(grid);

        background.add(BorderLayout.CENTER, mainPanel);

        for (int i = 0; i < 256; i++){
            JCheckBox c = new JCheckBox();
            c.setSelected(false);
            checkboxList.add(c);
            mainPanel.add(c);
        }

        setUpMidi();

        theFrame.setBounds(50, 50, 300, 300);
        theFrame.pack();
        theFrame.setVisible(true);
    }

    public void setUpMidi(){
        try {
            sequencer = MidiSystem.getSequencer();
            sequencer.open();
            sequence = new Sequence(Sequence.PPQ, 4);
            track = sequence.createTrack();
            sequencer.setTempoInBPM(120);
        } catch(Exception e){
            e.printStackTrace();
        }
    
    }

    public void buildTrackAndStart() {
        int[] trackList = null;
        
        sequence.deleteTrack(track);
        track = sequence.createTrack();

        for (int i = 0; i < 16; i++){
            trackList = new int[16];

            int key = instruments[i];

            for (int j=0; j<16; j++){
                JCheckBox jc = (JCheckBox)checkboxList.get(j + (16*i));
                if (jc.isSelected()) {
                    trackList[j] = key;
                }
                else {
                    trackList[j] = 0;
                }
            }
            makeTracks(trackList);
            track.add(makeEvent(176, 1, 127, 0, 16));
        }
        track.add(makeEvent(192, 9, 1, 0, 15));
        try {
            sequencer.setSequence(sequence);
            sequencer.setLoopCount(Sequencer.LOOP_CONTINUOUSLY);
            sequencer.start();
            sequencer.setTempoInBPM(120);
        } catch (Exception e){
            e.printStackTrace();
        }
    }

    public class MyStartListener implements ActionListener {
        public void actionPerformed(ActionEvent a){
            buildTrackAndStart();
        }
    }

    public class MyStopListener implements ActionListener {
        public void actionPerformed(ActionEvent a){
            sequencer.stop();
        }
    }

    public class MyUpTempoListener implements ActionListener {
        public void actionPerformed(ActionEvent a){
            float tempoFactor = sequencer.getTempoFactor();
            sequencer.setTempoFactor((float)(tempoFactor * 1.03));
        }
    }

    public class MyDownTempoListener implements ActionListener {
        public void actionPerformed(ActionEvent a){
            float tempoFactor = sequencer.getTempoFactor();
            sequencer.setTempoFactor((float)(tempoFactor * 0.97));
        }
    } 

    public void makeTracks(int[] list){
        for (int i = 0; i < 16; i++){
            int key = list[i];
            if (key != 0 ){
                track.add(makeEvent(144, 9, key, 100, i));
                track.add(makeEvent(128, 9, key, 100, i+1));
            }
        }
    }

    public MidiEvent makeEvent(int comd, int chan, int one, int two, int tick) {
        MidiEvent event = null;
        try {
            ShortMessage a = new ShortMessage();
            a.setMessage(comd, chan, one, two);
            event = new MidiEvent(a, tick);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return event;
    }
}