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

13.9 Case Study: The StillClock Class 501
5 public DisplayClock() {
6 // Create an analog clock for the current time
7 StillClock clock = new StillClock();
8
9 // Display hour, minute, and second in the message panel
10 MessagePanel messagePanel = new MessagePanel(clock.getHour() +
11 ":" + clock.getMinute() + ":" + clock.getSecond());
12 messagePanel.setCentered(true);
13 messagePanel.setForeground(Color.blue);
14 messagePanel.setFont(new Font("Courier", Font.BOLD, 16));
15
16 // Add the clock and message panel to the frame
17 add(clock);
18 add(messagePanel, BorderLayout.SOUTH);
19 }
20
21 public static void main(String[] args) {
22 DisplayClock frame = new DisplayClock();
23 frame.setTitle("DisplayClock");
24 frame.setSize(300, 350);
25 frame.setLocationRelativeTo(null); // Center the frame
26 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
27 frame.setVisible(true);
28 }
29 }
create a clock
create a message panel
add a clock
add a message panel
(0, 0)
(xEnd, yEnd)
12
handLength
9 3
(xCenter, yCenter)
6
(a)
FIGURE 13.21 (a) The DisplayClock program displays a clock that shows the current
time. (b) The endpoint of a clock hand can be determined, given the spanning angle, the
hand length, and the center point.
(b)
The rest of this section explains how to implement the StillClock class. Since you can use
the class without knowing how it is implemented, you may skip the implementation if you
wish.
To draw a clock, you need to draw a circle and three hands for the second, minute, and
hour. To draw a hand, you need to specify the two ends of the line. As shown in Figure
13.21b, one end is the center of the clock at (xCenter, yCenter); the other end, at
(xEnd, yEnd), is determined by the following formula:
skip implementation?
implementation
xEnd = xCenter + handLength × sin(θ)
yEnd = yCenter - handLength × cos(θ)
Since there are 60 seconds in one minute, the angle for the second hand is
second × (2π/60)