Caution
Note
Note
518 Chapter 15 Graphics
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handLength
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(a) |
(b) |
FIGURE 15.22 (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.
The position of the minute hand is determined by the minute and second. The exact minute value combined with seconds is minute + second/60. For example, if the time is 3 minutes and 30 seconds, the total minutes are 3.5. Since there are 60 minutes in one hour, the angle for the minute hand is
(minute + second/60) × (2π/60)
Since one circle is divided into 12 hours, the angle for the hour hand is
(hour + minute/60 + second/(60 × 60)) × (2π/12)
For simplicity in computing the angles of the minute hand and hour hand, you can omit the seconds, because they are negligibly small. Therefore, the endpoints for the second hand, minute hand, and hour hand can be computed as:
xSecond = xCenter + secondHandLength × sin(second × (2π/60)) ySecond = yCenter - secondHandLength × cos(second × (2π/60)) xMinute = xCenter + minuteHandLength × sin(minute × (2π/60)) yMinute = yCenter - minuteHandLength × cos(minute × (2π/60))
xHour = xCenter + hourHandLength × sin((hour + minute/60) × (2π/60)) yHour = yCenter - hourHandLength × cos((hour + minute/60) × (2π/60))
The StillClock class is implemented in Listing 15.10.
LISTING 15.10 StillClock.java
1 import java.awt.*;
2 import javax.swing.*;
3 import java.util.*;
4
5 public class StillClock extends JPanel {
6 private int hour;
7 private int minute;
8 private int second;
9
10/** Construct a default clock with the current time*/
11public StillClock() {
12setCurrentTime();
13}
14
15 /** Construct a clock with specified hour, minute, and second */
15.10 Case Study: The StillClock Class 519
16public StillClock(int hour, int minute, int second) {
17this.hour = hour;
18this.minute = minute;
19this.second = second;
20}
21
22/** Return hour */
23public int getHour() {
24return hour;
25}
26
27/** Set a new hour */
28public void setHour(int hour) {
29this.hour = hour;
30 |
repaint(); |
repaint panel |
31 |
} |
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32 |
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33/** Return minute */
34public int getMinute() {
35return minute;
36}
37
38/** Set a new minute */
39public void setMinute(int minute) {
40this.minute = minute;
41 |
repaint(); |
repaint panel |
42 |
} |
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43 |
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44/** Return second */
45public int getSecond() {
46return second;
47}
48
49/** Set a new second */
50public void setSecond(int second) {
51this.second = second;
52 |
repaint(); |
repaint panel |
53 |
} |
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54 |
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55 |
/** Draw the clock */ |
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56 |
protected void paintComponent(Graphics g) { |
override paintComponent |
57 |
super.paintComponent(g); |
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58 |
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59// Initialize clock parameters
60int clockRadius =
61(int)(Math.min(getWidth(), getHeight()) * 0.8 * 0.5);
62int xCenter = getWidth() / 2;
63int yCenter = getHeight() / 2;
64
65// Draw circle
66g.setColor(Color.BLACK);
67g.drawOval(xCenter - clockRadius, yCenter - clockRadius,
682 * clockRadius, 2 * clockRadius);
69g.drawString("12", xCenter - 5, yCenter - clockRadius + 12);
70g.drawString("9", xCenter - clockRadius + 3, yCenter + 5);
71g.drawString("3", xCenter + clockRadius - 10, yCenter + 3);
72g.drawString("6", xCenter - 3, yCenter + clockRadius - 3);
74// Draw second hand
75int sLength = (int)(clockRadius * 0.8);