Run the ClickMe Applets

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Note: The applets on this page require JDK 1.1. If you are using an older browser that does not support 1.1, you won't be able to run the applets. Instead, you need to view this page in a 1.1 browser, such as HotJava, the JDK Applet Viewer (appletviewer), or certain versions of Netscape Navigator and Internet Explorer. For more information about running applets, refer to About Our Examples.

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ClickMe

This is the original applet. Click within the applet's bounds and the applet displays a red spot at the mouse click location.

ClickMeGreen

This applet is a minor modification of the original. Besides the applet name, only the code that draws the spot changed. The following table shows the spot-drawing code from both versions of the applet.

Old Version	New Version
g.setColor(Color.red); if (spot != null) { g.fillOval(spot.x - RADIUS, spot.y - RADIUS, RADIUS * 2, RADIUS * 2); }	g.setColor(Color.green); if (spot != null) { g.fillRect(spot.x - RADIUS, spot.y - RADIUS, RADIUS * 2, RADIUS * 2); }

ClickMePurple

This is another relatively minor modification of the original applet. The differences between the two versions are shown in red:

Old Version

New Version

import java.applet.Applet; import java.awt.*; import java.awt.event.*; public class ClickMe extends Applet implements MouseListener { private Spot spot = null; private static final int RADIUS = 7; public void init() { addMouseListener(this); } public void paint(Graphics g) { // draw black border and white background ... // draw the spot g.setColor(Color.red); if (spot != null) { g.fillOval(spot.x - RADIUS, spot.y - RADIUS, RADIUS * 2, RADIUS * 2); } } public void mousePressed(MouseEvent event) { if (spot == null) { spot = new Spot(RADIUS); } spot.x = event.getX(); spot.y = event.getY(); repaint(); } ... }

import java.applet.Applet; import java.awt.*; import java.awt.event.*; public class ClickMePurple extends Applet implements MouseListener { private Spot spot = null; private Color purple = new Color(0.5f, 0.0f, 0.5f); public void init() { addMouseListener(this); } public void paint(Graphics g) { // draw black border and white background ... // draw the spot g.setColor(purple); if (spot != null) { g.drawString("Mary", spot.x, spot.y); } } public void mousePressed(MouseEvent event) { if (spot == null) { spot = new Spot(0); } spot.x = event.getX(); spot.y = event.getY(); repaint(); } ... }

ClickMeErase

The code for this applet differs from the original in the following ways:

• Adds another Spot object that tracks the spot's previous location.
• Adds an update method, which erases the old spot by drawing a white spot at the spot's previous location.
• Modifies the paint method to draw the white background and black border.
• Modifies the mousePressed method to store the spot's previous position before setting its new position.

ClickMeDrag

We used the solution to the previous exercise, ClickMeErase, as the basis to our solution for this one. These two programs differ in the following ways:

• The applet now implements two interfaces: MouseListener and MouseMotionListener.
• The applet registers itself twice. Once as a mouse listener and once as a mouse motion listener.
• The applet provides two new methods. The first, mouseDragged, has the same implementation as the mousePressed method, it moves the spot and repaints the applet. The second, mouseMoved, has an empty implementation because the applet doesn't care about mouse moved events.