Re: Help with Java school program

Question

Hi, I've been trying to figure out how to make my DoubleCanvas java program to work. What I'm supposed to do is have a left canvas and a right canvas. In the middle of the applet is a button panel that can select to either draw on the left, right, or both canvases. We have a main DoubleCanvas applet class, then each canvas is drawn from a MyCanvas class. My problem is I don't know how to switch from one canvas to the other canvas from the MyCanvas class.
Any help would be much appreciated. Thanks. :)

Answer 1

Hi, sorry. I didn't want to clutter the page with stuff that might be wrong. This is my DoubleCanvas applet class in the works. I'm not sure I did the listeners correct. And I haven't gotten to add the Checkbox event stuff in the MyCanvas class in yet, because I don't know how to make the checkboxes activate a particular canvas. If you feel I should post the MyCanvas class please let me know, it's somewhat long.
DoubleCanvas class
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.lang.*;
import java.math.*;
public class DoubleCanvas extends Applet
// ---- class and instance objects ----
private Panel button_panel;
private MyCanvas drawing_canvas1, drawing_canvas2;
private CheckboxGroup canvas;
private Checkbox left, right, both;
private Choice color_choices;
private Button undo_but, redo_but, erase_but;
public void init()
color_choices = new Choice();
color_choices.add("white");
color_choices.add("yellow");
color_choices.add("gray");
color_choices.add("magenta");
erase_but = new Button("erase");
undo_but = new Button("undo");
redo_but = new Button("redo");
canvas = new CheckboxGroup();
left = new Checkbox ( "<-", true, canvas );
right = new Checkbox ( "->", false, canvas );
both = new Checkbox ( "<->", false, canvas );
button_panel = new Panel();
drawing_canvas1 = new MyCanvas();
drawing_canvas2 = new MyCanvas();
drawing_canvas1.setBackground(Color.black);
drawing_canvas2.setBackground(Color.black);
setLayout( new GridLayout(1,3) );
button_panel.setLayout( new GridLayout(7,1) );
button_panel.add( left );
button_panel.add( right );
button_panel.add( both );
button_panel.add( color_choices );
button_panel.add( erase_but );
button_panel.add( undo_but );
button_panel.add( redo_but );
add( drawing_canvas1 );
add( button_panel );
add( drawing_canvas2 );
left.addItemListener( drawing_canvas1 );
right.addItemListener( drawing_canvas1 );
both.addItemListener( drawing_canvas1 );
color_choices.addItemListener( drawing_canvas1 );
erase_but.addActionListener( drawing_canvas1);
undo_but.addActionListener( drawing_canvas1 );
redo_but.addActionListener( drawing_canvas1 );
public void paint( Graphics g ) {