Prentice.Hall.Introduction.to.Java.Programming,.Brief.Version.9th.(2014).[sharethefiles.com]

13.8 Case Study: The MessagePanel Class 495
This is a MessagePanel object
stringWidth()
getHeight() stringAscent()
(xCoordinate, yCoordinate)
xCoordinate = getWidth / 2 - stringWidth / 2;
yCoordinate = getHeight / 2 - stringAscent / 2;
FIGURE 13.17 The program uses the FontMetrics class to measure the string width and
height and displays it at the center of the panel.
The methods getWidth() and getHeight() (lines 36–37) defined in the Component class
return the component’s width and height, respectively.
Since the message is centered, the first character of the string should be positioned at
(xCoordinate, yCoordinate), as shown in Figure 13.17.
13.19 How do you find the leading, ascent, descent, and height of a font?
13.20 How do you find the exact length in pixels of a string in a Graphics object?
13.8 Case Study: The MessagePanel Class
This case study develops a useful class that displays a message in a panel. The class
enables the user to set the location of the message, center the message, and move the
message a specified interval.
The contract of the MessagePanel class is shown in Figure 13.18.
Let us first write a test program in Listing 13.7 that uses the MessagePanel class to display
four message panels, as shown in Figure 13.19.
LISTING 13.7
TestMessagePanel.java
1 import java.awt.*;
2 import javax.swing.*;
3
4 public class TestMessagePanel extends JFrame {
5 public TestMessagePanel() {
6 MessagePanel messagePanel1 = new MessagePanel("Welcome to Java") ;
7 MessagePanel messagePanel2 = new MessagePanel("Java is fun");
8 MessagePanel messagePanel3 = new MessagePanel("Java is cool");
9 MessagePanel messagePanel4 = new MessagePanel("I love Java");
10 messagePanel1.setFont(new Font("SansSerif", Font.ITALIC, 20));
11 messagePanel2.setFont(new Font("Courier", Font.BOLD, 20));
12 messagePanel3.setFont(new Font("Times", Font.ITALIC, 20));
13 messagePanel4.setFont(new Font("Californian FB", Font.PLAIN, 20));
14 messagePanel1.setBackground(Color.RED);
15 messagePanel2.setBackground(Color.CYAN);
16 messagePanel3.setBackground(Color.GREEN);
17 messagePanel4.setBackground(Color.WHITE);
✓Point✓ Check
Key
Point
VideoNote
The MessagePanel class
create message panel
set font
set background