题外话：正好赶上OperatingSystem的作业要做一个模拟线程/进程调度的问题，决定用JAVA实现才发现这些内容和之前学过的GUI制作是两码事儿- -b
通过学习java.swing库的ActionListener接口我们初步了解了一些关于java框体程序的各个部件JFrame,JPanel,JComponent和控件之间是如何联系通讯的，然而这次我们要从另一个视角来看java程序框体。
从一个框体实现“表”的代码我们来初步看一下java是如何在JFrame平台上制作出自己想要的图案的吧！
（实现效果图）
有几个可能会比较陌生的类先筛选出来：
（1）GeneralPath：是java.awt.geom.Path2D的一个子类，path的设定过程主要用两个函数moveTo（double x，double y）和linkTo（double x，double y），当然如果需要实现path的动态绘制的话需要的方法远不止这两个，可以自行去javadoc查阅。
（2）Ellipse2D:是java.awt.geom下的一个类，可以用来绘制理论上的椭圆构造参数为（double x，double y，double width，double height）意义不多赘述。
（3）AffineTransform：这个是整个代码中最有分量的一个类，这个类的引用的获取方法是用静态方法AffineTransform.getInstance（double theta，double x，double y）这里的x和y指的是锚点也就是整个旋转过程参照的旋转中心，theta是要用弧度制表示的旋转角度。具体使用方法下文中会详细总结。
（4）Timer类是在我接触到的新的控件，和JButton或者JLabel等等不同的是这个空间不要手动加上ActionListener的接口来进行事件驱动。使用方法在代码中有详述。
1 import java.awt.*;View Code
2 import java.awt.event.*;
3 import java.awt.geom.*;
4 import java.util.Calendar;
5 import javax.swing.*;
6
7 public class Main extends JPanel implements ActionListener
8 {
9 // Create a shape for the face of the clock
10 protected static Ellipse2D face = new Ellipse2D.Float(3, 3, 94, 94);
11
12 // Create a path that represents a tick mark
13 protected static GeneralPath tick = new GeneralPath();
14 static
15 {
16 tick.moveTo(100, 100);
17 tick.moveTo(49, 0);
18 tick.lineTo(51, 0);
19 tick.lineTo(51, 6);
20 tick.lineTo(49, 6);
21 tick.lineTo(49, 0);
22
23 }
24
25 // Create a cool hour hand
26 protected static GeneralPath hourHand = new GeneralPath();
27 static
28 {
29 hourHand.moveTo(50, 15);
30 hourHand.lineTo(53, 50);
31 hourHand.lineTo(50, 53);
32 hourHand.lineTo(47, 50);
33 hourHand.lineTo(50, 15);
34 }
35
36 // Create a cool minute hand
37 protected static GeneralPath minuteHand = new GeneralPath();
38 static
39 {
40 minuteHand.moveTo(50, 2);
41 minuteHand.lineTo(53, 50);
42 minuteHand.lineTo(50, 58);
43 minuteHand.lineTo(47, 50);
44 minuteHand.lineTo(50, 2);
45 }
46
47 // And a cool second hand
48 protected static GeneralPath secondHand = new GeneralPath();
49 static
50 {
51 secondHand.moveTo(49, 5);
52 secondHand.lineTo(51, 5);
53 secondHand.lineTo(51, 62);
54 secondHand.lineTo(49, 62);
55 secondHand.lineTo(49, 5);
56 }
57
58 // Create some colors for the pieces of the clock
59 protected static Color faceColor = new Color(220, 220, 220);
60 protected static Color hourColor = Color.red.darker();
61 protected static Color minuteColor = Color.blue.darker();
62 protected static Color secondColor = new Color(180, 180, 0);
63 protected static Color pinColor = Color.gray.brighter();
64
65 // Create circles for the pivot and center pin
66 protected Ellipse2D pivot = new Ellipse2D.Float(47, 47, 6, 6);
67 protected Ellipse2D centerPin = new Ellipse2D.Float(49, 49, 2, 2);
68
69
70 // Create three transforms that center around the pivot point
71 protected AffineTransform hourTransform =
72 AffineTransform.getRotateInstance(0, 50, 50);
73 protected AffineTransform minuteTransform =
74 AffineTransform.getRotateInstance(0, 50, 50);
75 protected AffineTransform secondTransform =
76 AffineTransform.getRotateInstance(0,50,50);
77
78 // Create a timer that fires once a second and a Calendar
79 // instance for getting the time values
80 protected Timer timer = new Timer(1000, this);
81 protected Calendar calendar = Calendar.getInstance();
82
83 // Constructor - hardcode a preferred size of 100x100
84 public Main()
85 {
86 setPreferredSize(new Dimension(100, 100));
87 }
88
89 // Invoked when panel is added to a container
90 public void addNotify()
91 {
92 // Call the superclass and start the timer
93 super.addNotify();
94 timer.start();
95 }
96
97 // Invoked when panel is removed from a container
98 public void removeNotify()
99 {
100 // Call the superclass and stop the timer
101 timer.stop();
102 super.removeNotify();
103 }
104
105 //
106 public void actionPerformed(ActionEvent event)
107 {
108 // Update the calendar's time
109 this.calendar.setTime(new java.util.Date());
110
111 // Extract the hours minutes and seconds
112 int hours = this.calendar.get(Calendar.HOUR);
113 int minutes = this.calendar.get(Calendar.MINUTE);
114 int seconds = this.calendar.get(Calendar.SECOND);
115
116 // Using a little trigonometry, set the transforms to rotate
117 // each hand into the proper position. Center the rotation
118 // around the pivot point (50, 50) instead of the origin
119 hourTransform.setToRotation(((double) hours) *
120 (Math.PI / 6.0), 50, 50);
121 minuteTransform.setToRotation(((double) minutes) *
122 (Math.PI / 30.0), 50, 50);
123 secondTransform.setToRotation(((double) seconds) *
124 (Math.PI / 30.0), 50, 50);
125
126 // Force the component to repaint ASAP
127 repaint();
128 }
129
130 // This is an alternative to creating a UI delegate. Since JPanel's
131 // paint() method only paints the border and backgound, we can just
132 // override the paint method of the component to do the graphics.
133 public void paint(Graphics g)
134 {
135 // Call the superclass first to paint the border (if one is assigned)
136 super.paint(g);
137
138 // Get the graphics context and turn on anti-aliasing
139 Graphics2D g2 = (Graphics2D) g;
140 g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
141 RenderingHints.VALUE_ANTIALIAS_ON);
142
143 // Set the paint for the clock face and fill it in
144 g2.setPaint(faceColor);
145 g2.fill(face);
146
147 // Set the paint to black and draw the clock's outline
148 g2.setPaint(Color.black);
149 g2.draw(face);
150
151 // Fill in the 12 ticks around the face of the clock
152 for (double p = 0.0; p < 12.0; p += 1.0)
153 {
154 // This is probably terribly inefficient and should be
155 // done statically or in the constructor - draw the
156 // tick as a transformed shape that is rotated.
157 g2.fill(tick.createTransformedShape(
158 AffineTransform.getRotateInstance((Math.PI / 6.0) * p,
159 50, 50)));
160 }
161
162 // Set the paint and draw the hour hand. It is lowest in the
163 // 'z-order' so will appear underneath the other hands. Notice
164 // how each hand is transformed by a different <AffineTransform>.
165 g2.setPaint(hourColor);
166 g2.fill(hourHand.createTransformedShape(hourTransform));
167
168 // Set the paint and draw the minute hand, the second hand,
169 // the pivot and the center pin
170 g2.setPaint(minuteColor);
171 g2.fill(minuteHand.createTransformedShape(minuteTransform));
172 g2.setPaint(secondColor);
173 g2.fill(secondHand.createTransformedShape(secondTransform));
174 g2.fill(pivot);
175 g2.setPaint(pinColor);
176 g2.fill(centerPin);
177 }
178
179 // A little test frame to show off our fancy clock
180 public static void main(String[] args)
181 {
182 JFrame frame = new JFrame();
183 frame.setLocation(700, 400);
184 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
185 frame.getContentPane().add(new Main());
186 frame.pack();
187 frame.show();
188 }
189 }
Okay，Here are the points :-P
下面进阶深入探究一下这段代码：
#1#关于每次图形变换之后，变化前图形的擦除？
Ans：是这样的，一般来讲有两种办法实现所谓的擦除效果以完成动画：
1.手动擦除，直接对这个paint出来的geom下的类调用clear**方法，或者直接使用新的颜色/画布将需要擦除的形状删除/覆盖。
2.super.paint（g）这个方法有点神奇，以后需要进一步探讨一下，直接在子类的paint方法之中调用父类的paint的方法来实现“擦除”。
代码中方法其实是第一种，在每次repaint过程中，都会有一次将整个表盘“覆盖”重画的过程，但是不得不说，这么实现的话每秒钟都需要对整个表盘全部的空间进行重画，是很浪费时间/空间的。
#2#怎么递推实现的表盘圆周上的12个标记的绘制？
Ans：这里用了一个新的类叫做AffineTransform。使用这个类的方法是在geom下的几何类中直接调用createTransformedShape（AffineTransform at）返回一个Shape类型，这时匿名调用这个类进行draw（勾勒轮廓）/fill（填充颜色）方法可以完成对转换完成之后的几何体的绘制。关于AffineTransform类的更多用法和数学解释：
http://www.apihome.cn/api/java/AffineTransform.html
#3#怎么实现消除斜线的锯齿状？
Ans：这个我真的不懂，但是我知道是下面这段神奇的代码起到的作用,至于这个“渲染提示”具体的用法还得慢慢学..
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
#4#阿西巴，addNotify方法到底有没有用？
Ans：addNotify方法是在JPanel添加到JComponent上的时候用的，本例中是在添加pane的直接启动计时器（Timer），关于代码最后那个若有若无的getContentPane（）为什么会出现，其实还要从JFrame的四层结构开始说起（传送门见下）：
http://tieba.baidu.com/p/2004216123