Java Reference
In-Depth Information
on a button or typing the E key. As you'll see, the applet overrides methods to
handle mouse events, keyboard events, and action events generated by the
Button
component. In particular, note the
boolean
return values of these event handling
methods. This applet does not define a
paint()
method. For simplicity, it does its
drawing directly in response to the events it receives and does not store the coor-
dinates. This means that it cannot regenerate the user's drawing if it is scrolled off
the screen and then scrolled back on.
Example 15−3: Scribble.java
package com.davidflanagan.examples.applet;
import java.applet.*;
import java.awt.*;
/**
* This applet lets the user scribble with the mouse.
* It demonstrates the Java 1.0 event model.
**/
public class Scribble extends Applet {
private int lastx, lasty;
// Remember last mouse coordinates.
Button erase_button;
// The Erase button.
/** Initialize the erase button, ask for keyboard focus */
public void init() {
erase_button = new Button("Erase");
this.add(erase_button);
this.setBackground(Color.white); // Set background color for scribble
this.requestFocus(); // Ask for keyboard focus so we get key events
}
/** Respond to mouse clicks */
public boolean mouseDown(Event e, int x, int y) {
lastx = x; lasty = y;
// Remember where the click was
return true;
}
/** Respond to mouse drags */
public boolean mouseDrag(Event e, int x, int y) {
Graphics g = getGraphics();
g.drawLine(lastx, lasty, x, y);
// Draw from last position to here
lastx = x; lasty = y;
// And remember new last position
return true;
}
/** Respond to key presses: Erase drawing when user types 'e' */
public boolean keyDown(Event e, int key) {
if ((e.id == Event.KEY_PRESS) && (key == 'e')) {
Graphics g = getGraphics();
g.setColor(this.getBackground());
g.fillRect(0, 0, bounds().width, bounds().height);
return true;
}
else return false;
}
/** Respond to Button clicks: erase drawing when user clicks button */
public boolean action(Event e, Object arg) {
if (e.target == erase_button) {
Graphics g = getGraphics();
