Getting Array Index Out of Bound Exception and Can't Find the Source

Question

This program compiles just fine. It is one of the tutorial programs from Head First Java and I'm pretty sure I typed it up correctly but I am getting the index out of bounds error. I know what this error means but, for the life of me, I can't see where I am going wrong.

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 High-Hat",
    "Open Hi-Hat", "Acoustic Snare", "Crash Cymbal", "Hand Clap",
    "High Tom", "High Bongo", "Maracas", "Whistle", "Low Conga",
    "Open High 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){
        BeatBox box = new BeatBox();
        box.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(20,20);
        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 * .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;
    }
}

Answer 1

This:

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

You have only 12 elements in instrumentNames , so you can only loop from 0 to 11. When you try to access instrumentNames[12] you get the ArrayIndexOutOfBoundsException .

Use the array length instead:

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

Or the for-each loop:

for (String instrumentName : instrumentNames) {
    nameBox.add(new Label(instrumentName));
}