Canvas Example

/*
	Example illustrating the use of canvases.
	
	This applet has two canvases (of two different kinds)
	The basic fuinctionality is implemented here for illustration
	purposes. Experiment with this...to learn more!
*/

import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;

public class CanvasExample extends Applet implements ActionListener {

	// GUI Widgets
	Button goButton;
	leftCanvas L;
	rightCanvas R;
	
	public void init() {
	
		setLayout(new BorderLayout());
		
		goButton = new Button("Do it again!");
		Panel bPanel = new Panel();
		bPanel.add(goButton);
		add("South", bPanel);
		goButton.addActionListener(this);
		
		// add the two canvases
		Panel centerPanel = new Panel();
		centerPanel.setLayout(new GridLayout(1,2));
		
		L = new leftCanvas();
		R = new rightCanvas();
		centerPanel.add(L);
		centerPanel.add(R);
		
		add("Center", centerPanel);
	} // init
	
	public void actionPerformed(ActionEvent e) {
	
		if (e.getSource() == goButton) {
			repaint();		// repaint this applet
			L.repaint();	// also repaint the canvases
			R.repaint();	// repaint canvases
		}
			
	} // actionPerformed

} // CanvasExample

public class leftCanvas extends Canvas {
	// Every left canvas has a random colored oval in it
	// every time it is repainted, it is generated and painted
	
	int h, w;			// the height and width of this canvas
	

	
	public void paint(Graphics win) {
		int ovalDia;
		int r, g, b;
		int x, y;
		
		// set the height and width of this canvas
		// this depends on where it is added, so we'll use
		// getSize to get its dimensions
		h = getSize().height;
		w = getSize().width;
		win.drawRect(0,0, w-1, h-1);	// Draw border
		
		// draw a random colored oval
		ovalDia = (int) (Math.random()*(w/4));
		x = (int) (Math.random()*w);
		y = (int) (Math.random()*h);
		
		r = (int) (Math.random()*256);
		g = (int) (Math.random()*256);
		b = (int) (Math.random()*256);
		
		win.setColor(new Color(r, g, b));
		win.fillOval(x, y, ovalDia, ovalDia);
		
	} // paint

} // leftCanvas

public class rightCanvas extends Canvas {
	// Every left canvas has a random colored box in it
	// every time it is repainted, it is generated and painted
	
	int h, w;			// the height and width of this canvas
	
	public void paint(Graphics win) {
		int boxSize;
		int r, g, b;
		int x, y;
		
		// set the height and width of this canvas
		// this depends on where it is added, so we'll use
		// getSize to get its dimensions
		h = getSize().height;
		w = getSize().width;
		win.drawRect(0,0, w-1, h-1);		// Draw border
		
		// draw a random colored box
		boxSize = (int) (Math.random()*(w/4));
		x = (int) (Math.random()*w);
		y = (int) (Math.random()*h);
		
		r = (int) (Math.random()*256);
		g = (int) (Math.random()*256);
		b = (int) (Math.random()*256);
		
		win.setColor(new Color(r, g, b));
		win.fillRect(x, y, boxSize, boxSize);
		
	} // paint

} // leftCanvas