APPLETS AND MULTIMEDIA - Introduction to Java Programming - page 683

18.14

What is wrong if the DisplayMessage applet is revised as follows?

public class DisplayMessage extends JApplet {
/** Initialize the applet */
public DisplayMessage() {
// Get parameter values from the HTML file
String message = getParameter( "MESSAGE" );
int x =
Integer.parseInt(getParameter( "X" ));
int y =
Integer.parseInt(getParameter( "Y" ));

public class DisplayMessage extends JApplet {
private String message;
private int x;
private int y;

@Override /** Initialize the applet */
public void init() {
// Get parameter values from the HTML file
message = getParameter( "MESSAGE" );
x = Integer.parseInt(getParameter( "X" ));
y = Integer.parseInt(getParameter( "Y" )); // Create a message panel

MessagePanel messagePanel =
new MessagePanel(message);
messagePanel.setXCoordinate(x);
messagePanel.setYCoordinate(y);

}

public DisplayMessage() {
// Create a message panel
MessagePanel messagePanel =
new MessagePanel(message);
messagePanel.setXCoordinate(x);
messagePanel.setYCoordinate(y);

// Add the message panel to the applet
add(messagePanel);

}

}

// Add the message panel to the applet
add(messagePanel);

}

}

(a) Revision 1

(b) Revision 2

18.8 Case Study: Bouncing Ball
This section presents an applet that displays a ball bouncing in a panel.

Key
Point

The applet uses two buttons to suspend and resume the bouncing movement, and uses a scroll
bar to control the bouncing speed, as shown in Figure 18.8.

F IGURE 18.8

The ball's movement is controlled by the Suspend and Resume buttons and the

scroll bar.

Here are the major steps to write this program:

1. Define a subclass of JPanel named Ball to display a ball bouncing, as shown in
Listing 18.7.

2. Define a subclass of JPanel named BallControl to set the ball speed with a scroll
bar, and two control buttons Suspend and Resume , as shown in Listing 18.8.

3. Define an applet named BounceBallApp to contain an instance of BallControl and
enable the applet to run as a standalone application, as shown in Listing 18.9.

The relationship among these classes is shown in Figure 18.9.