Java基础之在窗口中绘图——绘制圆弧和椭圆（Sketcher 3 drawing arcs and ellipses）

 1 import javax.swing.JComponent;
 2 import java.util.*;
 3 import java.awt.*;
 4 import java.awt.geom.*;
 5 
 6 @SuppressWarnings("serial")
 7 public class SketcherView extends JComponent implements Observer {
 8   public SketcherView(Sketcher theApp) {
 9     this.theApp = theApp;
10   }
11 
12   // Method called by Observable object when it changes
13   public void update(Observable o, Object rectangle) {
14     // Code to respond to changes in the model...
15   }
16 
17   // Method to draw on the view
18   @Override
19   public void paint(Graphics g) {
20     // Temporary code...
21     Graphics2D g2D = (Graphics2D)g;                                    // Get a Java 2D device context
22     Point2D.Double position = new Point2D.Double(50,10);               // Initial position
23     double width = 150;                                                // Width of ellipse
24     double height = 100;                                               // Height of ellipse
25     double start = 30;                                                 // Start angle for arc
26     double extent = 120;                                               // Extent of arc
27     double diameter = 40;                                              // Diameter of circle
28 
29     // Define open arc as an upper segment of an ellipse
30     Arc2D.Double top = new Arc2D.Double(position.x, position.y,
31                                      width, height,
32                                      start, extent,
33                                      Arc2D.OPEN);
34 
35     // Define open arc as lower segment of ellipse shifted up relative to 1st
36     Arc2D.Double bottom = new Arc2D.Double(
37                                      position.x, position.y - height + diameter,
38                                      width, height,
39                                      start + 180, extent,
40                                      Arc2D.OPEN);
41 
42     // Create a circle centered between the two arcs
43     Ellipse2D.Double circle1 = new Ellipse2D.Double(
44                                      position.x + width/2 - diameter/2,position.y,
45                                      diameter, diameter);
46 
47     // Create a second circle concentric with the first and half the diameter
48     Ellipse2D.Double circle2 = new Ellipse2D.Double(
49                    position.x + width/2 - diameter/4, position.y + diameter/4,
50                    diameter/2, diameter/2);
51 
52     // Draw all the shapes
53     g2D.setPaint(Color.BLACK);                                         // Draw in black
54     g2D.draw(top);
55     g2D.draw(bottom);
56 
57     g2D.setPaint(Color.BLUE);                                          // Draw in blue
58     g2D.draw(circle1);
59     g2D.draw(circle2);
60     g2D.drawString("Arcs and ellipses", 80, 100);                      // Draw some text
61 
62   }
63 
64   private Sketcher theApp;                                             // The application object
65 }