CheckBox reader and other bits

Question

Hi
I'm a perl srcipter so I get the basics of programming even if I've got the java terminology wrong. I have a table with 4 rows 5 columns, I want to draw each row as a line on a graph and I want to be able to control which row(s) are displayed with checkboxes. The code below compiles as it stands so hopefully you can see what I'm trying to do. I have the following issues which I've been unable to sort and hope someone will point me the right way.
Reading the checkbox events. My plan was for a boolean array (checkBoxSetting[]) which recorded true/false for each line on the graph then I could print 'if true'. Do I need to somehow call the 'itemStateChanged' method (line 7 from within the arrayExp() method (line 112)? Do I need the block commented out at lines 60-65 and if so what causes the error "addItemListener(java.awt.event.ItemListener) in javax.swing.AbstractButton cannot be applied to (arrayExp)"? Am I any where close to getting this working?
Other problems...
Line 124 I changed from grid layout to box layout so I don't think I sould need this line but if I comment it out I get a very small panel with nothing on it. So what should I put insead?
Line 163 I need to scale the data by dividing the height of the y axis by the highest data value. With the test data that should be 200/400 = 0.5 but whatever I define scale as (double, float, int) I get zero as the result? (thus it's currently over written on line 164)
I find testing as an application easyer so I plan to convert this to an applet once I've got it working. Is that a bad plan, should I just make it into an applet now the worry about functionality later?
Any help on the above problems would be appreciated and if you want to advise on other glaring errors in my structure please do. Thanks Annie
  * 1.1 version.
import java.awt.*;
import java.awt.event.*;
import java.lang.Math;
import java.net.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
public class arrayExp extends Frame
                        implements ActionListener {
     boolean inAnApplet = true;
     JCheckBox ATButton;
     JCheckBox CdButton;
     JCheckBox CuButton;
     JCheckBox PAHButton;
     boolean[] checkBoxSetting = {true,true,true,true};
     public static void main(String[] args) {
          arrayExp window = new arrayExp();
          window.inAnApplet = false;
          window.setTitle("expressions");
          window.pack();
          window.setVisible(true);
     public void actionPerformed(ActionEvent event) {
          //The only action event we get is when the
          //user requests we bring up a FileDialog.
          FileDialog fd = new FileDialog(this, "FileDialog");
          fd.setVisible(true);
     public JPanel CheckBoxPanel() {
          //Create the check boxes.
          ATButton = new JCheckBox("AT");
          ATButton.setMnemonic(KeyEvent.VK_C);
          ATButton.setSelected(true);
          checkBoxSetting[0]=true;
          CdButton = new JCheckBox("Cd");
          CdButton.setMnemonic(KeyEvent.VK_G);
          CdButton.setSelected(true);
          checkBoxSetting[1]=true;
          CuButton = new JCheckBox("Cu");
          CuButton.setMnemonic(KeyEvent.VK_H);
          CuButton.setSelected(true);
          checkBoxSetting[2]=true;
          PAHButton = new JCheckBox("PAH");
          PAHButton.setMnemonic(KeyEvent.VK_T);
          PAHButton.setSelected(true);
          checkBoxSetting[3]=true;
/*          //Register a listener for the check boxes.
          ATButton.addItemListener(this);
          CdButton.addItemListener(this);
          CuButton.addItemListener(this);
          PAHButton.addItemListener(this);
          JPanel p = new JPanel();
          p.setLayout(new GridLayout(4,1));
          p.add(ATButton);
          p.add(CdButton);
          p.add(CuButton);
          p.add(PAHButton);
          return (p);
// add a checkbox listener
     public void itemStateChanged(ItemEvent event) {
          char c = '-';
          Object source = event.getItemSelectable();
          if (source == ATButton) {
               checkBoxSetting[0] = false;
               c = 'T';
               System.out.println("CheckBox "+c);
          else if (source == CdButton) {
               checkBoxSetting[1] = false;
               c = 'd';
               System.out.println("CheckBox "+c);
          else if (source == CuButton) {
               checkBoxSetting[2] = false;
               c = 'u';
               System.out.println("CheckBox "+c);
          else if (source == PAHButton) {
               checkBoxSetting[3] = false;
               c = 'H';
               System.out.println("CheckBox "+c);
          //Now that we know which button was pushed, find out
          //whether it was selected or deselected.
          if (event.getStateChange() == ItemEvent.DESELECTED) {
               System.out.println("CheckBox "+c);
               c = '-';
          repaint();
     public arrayExp() {
          Panel canvasPanel = new Panel();
          JPanel cbp = CheckBoxPanel();
          setLayout(new BorderLayout());
          //layout area as boxes left to right
          canvasPanel.setLayout(new BoxLayout(canvasPanel, BoxLayout.LINE_AXIS));
          //Put a graph (MyCanvas) in the first box.
          canvasPanel.add(new MyCanvas());
          //Put checkboxes in the right box.
          canvasPanel.add(cbp);
          add("East", canvasPanel);  //why do I need this when I changed to a box layout?
          addWindowListener(new WindowAdapter() {
               public void windowClosing(WindowEvent event) {
                    if (inAnApplet) {dispose();}
                    else {System.exit(0);}
}//----------------end class arrayExp
//paint the graph on a canvas.
class MyCanvas extends Canvas {
     public void paint(Graphics g) {
          System.out.println("Paint");
          //tempory array of expression levels for four treatments X 5 exposures
          //to be read from database in future
          int[][] expLevels =      {  {0, 50, 120, 200, 200},
                                             {20, 200, 100, 300, 200},
                                             {100, 100, 100, 400, 200},
                                             {0, 150, 200, 150, 0}  };
          //find max expression to scale y axis
          int max=0;
          for (int i=0; i<4; i++) {
               for (int j=0; j<5; j++){
                    if (expLevels[i][j]>max) {max=expLevels[i][j];}
          //origin (form top left x right, y down)
//      int w = getSize().width;
//      int h = getSize().height;
          int originX=50;
          int step=100;  //distance between exposures on x axis
          int height=200;
          int originY=height+originX;
          double scale=height/max;
          scale=0.5;
          g.drawString("height"+height+"/ max"+max+" = scale"+scale, 0, originY+60);
          //set up an array of 5 colours
          Color[] EColor = new Color[5];
          EColor[0]= new Color(200,0,255); //magenta
          EColor[1]= new Color(0,0,255);      //green
          EColor[2]= new Color(0,255,0);      //blue
          EColor[3]= new Color(230,230,0); //yellow
          //draw axis
          g.setColor(Color.black);
          g.drawLine(originX, originX, originX, originY);
          g.drawLine(originX, originY, originX+(step*4), originY);
          //lable x axis
          g.drawString("LC0", originX, originY+20);
          g.drawString("LC12.5", originX+step, originY+20);
          g.drawString("LC25", originX+(step*2), originY+20);
          g.drawString("LC37.5", originX+(step*3), originY+20);
          g.drawString("LC50", originX+(step*4), originY+20);
          g.drawString("Exposure", originX+(step*2), originY+40);
          //lable y axis
          int xs=originX; int ys=originY; int zs=(int)((max/height)*0.25);
//          g.drawString("x"+xs+" y"+ys+" zs"+zs+" max"+max+" scale"+scale, 0, originY+60);
          g.drawString("0", originX-15, originY);
          g.drawString(""+(int)(max*scale*0.25), originX-20, originY- (int) (max*scale*0.25));//400*.5=200*.25=50
          g.drawString(""+(int)(max*scale*0.50), originX-20, originY- (int) (max*scale*0.5));
          g.drawString(""+(int)(max*scale*0.75), originX-20, originY- (int) (max*scale*0.75));
          g.drawString(""+max, originX-20, originY- (int) (max*scale));
          g.drawString("Expression", originX-100, originY-(int)(height*0.5));
          int x=originX; int y;
          for (int i=0; i<4; i++) {
//               if (checkBoxSetting) {
                    g.setColor(EColor[i]);
                    for (int j=0; j<4; j++){
                         y=j+1;
                         g.drawLine(x,originY-(int)(expLevels[i][j]*scale), x+step, originY-(int)(expLevels[i][y]*scale));
                         x=x+step;
                    x=originX;
     //If we don't specify this, the canvas might not show up at all
     //(depending on the layout manager).
     public Dimension getMinimumSize() {return new Dimension(550,300);}
     //If we don't specify this, the canvas might not show up at all
     //(depending on the layout manager).
     public Dimension getPreferredSize() {return getMinimumSize();}
}//end-------------class MyCanvas

Answer 1

To address some of your questions:
Do I need the block commented out at lines 60-65 and if so what causes the error
"addItemListener(java.awt.event.ItemListener) in javax.swing.AbstractButton cannot be applied
to (arrayExp)"?Uncommenting that block would seem reasonable. However, you then have to make arrayExp implement ItemListener and provide an itemStateChanged(ItemEvent) method.
Note that this advice only applies while you're learning. For production-quality code I wouldn't have a component also be a listener, but I'd use an (anonymous, generally) inner class.
Line 163 I need to scale the data by dividing the height of the y axis by the highest data
value. With the test data that should be 200/400 = 0.5 but whatever I define scale as (double,
float, int) I get zero as the result?The problem is on the right hand side of the = sign. You're dividing an int by an int, and that performs integer division. The tidiest way of fixing this is to cast the expression after the / to double:           double scale=height/(double)max;Whenever division produces suspicious zeroes that's something to check.
if you want to advise on other glaring errors in my structure please do.MyCanvas seems to do an awful lot of work in the paint method. All of the bits which set up data should be pulled out, probably into the constructor. (Some people would disagree with me and have an init() method instead. There are pros and cons).