Head First Java - Beat Box - Instruments Invisible

[Aaron Eaton]

Hey all,

I'm using the Head First Java book and I'm understanding this language for the first time. I've run into the first problem that the errata or my own elbow-grease haven't been able to resolve.

Chapter 13 - Code Kitchen creates a "Beat Box"

I have a background JPanel with an East and West component. The nameBox on the West side is being drawn, but then disappears when the checkboxes are generated. If I resize the window (using the mouse) I can see the names appearing as the panel is re-drawn, but they disappear again once the checkboxes are placed.

Any ideas?

-Aaron.

code:

import java.awt.*;
import javax.swing.*;
import javax.sound.midi.*;
import java.util.*;
import java.awt.event.*;
 
public class BeatBox implements MetaEventListener {
  
    JPanel mainPanel;
    ArrayList checkboxList;
    int bpm=120;
    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 Congo", "Cowbell", "Vibraslap",
            "Lowmid 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");
            BorderLayout layout=new BorderLayout();
            JPanel background= new JPanel(layout);
            background.setBorder(BorderFactory.createEmptyBorder(10,10,10,10));
            
            checkboxList = new ArrayList();
            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]));
            
        } //close for loop
        
         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);
             
          } //end loop
             
         setUpMidi();
         
         theFrame.setBounds(50,50,300,300);
         theFrame.pack();
         theFrame.setVisible(true);
    } // closes method
      
    public void setUpMidi() {
        try {
            sequencer=MidiSystem.getSequencer();
            sequencer.open();
            sequencer.addMetaEventListener(this);
            sequence=new Sequence(Sequence.PPQ,4);
            track= sequence.createTrack();
            sequencer.setTempoInBPM(bpm);
            
        } catch(Exception e) {e.printStackTrace();}
    } // closes method
    
    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;
                    }
              } //closes inner for loop 
            
            makeTracks(trackList);
            
        } // closes outer for loop
        
        track.add(makeEvent(192,9,1,0,15));
        
        try { 
            
            sequencer.setSequence(sequence);
            sequencer.start();
            sequencer.setTempoInBPM(bpm);
        }  catch (Exception e) {e.printStackTrace();}
        
    } // closes buildTrackAndStart method
    
    public class MyStartListener implements ActionListener {
        public void actionPerformed(ActionEvent a) {
   
            buildTrackAndStart();
        }
    } // closes inner class
    
     public class MyStopListener implements ActionListener {
        public void actionPerformed(ActionEvent b) {
            sequencer.stop();
        }
    } // closes inner class
     
      public class MyUpTempoListener implements ActionListener {
        public void actionPerformed(ActionEvent c) {
            bpm+=3;
        }
    } // closes inner class
      
        public class MyDownTempoListener implements ActionListener {
        public void actionPerformed(ActionEvent d) {
            bpm-=3;
        }
    } // closes inner class
        
        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;
        }
        
        public void meta(MetaMessage message) {
            if (message.getType()==47) {
                sequencer.start();
                sequencer.setTempoInBPM(bpm);
            }
        }
} //closes class

[Campbell Ritchie]

Welcome to the Ranch.
I copied and pasted your posting, and didn't get your problem. Now, I can't get any music out of it, but that is presumably because I don't have the requisite midi resources.
CR