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

控制台程序。

 import javax.swing.JComponent;
 import java.util.*;
 import java.awt.*;
 import java.awt.geom.*;

 @SuppressWarnings("serial")
 public class SketcherView extends JComponent implements Observer {
   public SketcherView(Sketcher theApp) {
     this.theApp = theApp;
   }

   // Method called by Observable object when it changes
   public void update(Observable o, Object rectangle) {
     // Code to respond to changes in the model...
   }

   // Method to draw on the view
   @Override
   public void paint(Graphics g) {
     // Temporary code...
     Graphics2D g2D = (Graphics2D)g;                                    // Get a Java 2D device context
     Point2D.Double position = new Point2D.Double(50,10);               // Initial position
     double width = 150;                                                // Width of ellipse
     double height = 100;                                               // Height of ellipse
     double start = 30;                                                 // Start angle for arc
     double extent = 120;                                               // Extent of arc
     double diameter = 40;                                              // Diameter of circle

     // Define open arc as an upper segment of an ellipse
     Arc2D.Double top = new Arc2D.Double(position.x, position.y,
                                      width, height,
                                      start, extent,
                                      Arc2D.OPEN);

     // Define open arc as lower segment of ellipse shifted up relative to 1st
     Arc2D.Double bottom = new Arc2D.Double(
                                      position.x, position.y - height + diameter,
                                      width, height,
                                      start + 180, extent,
                                      Arc2D.OPEN);

     // Create a circle centered between the two arcs
     Ellipse2D.Double circle1 = new Ellipse2D.Double(
                                      position.x + width/2 - diameter/2,position.y,
                                      diameter, diameter);

     // Create a second circle concentric with the first and half the diameter
     Ellipse2D.Double circle2 = new Ellipse2D.Double(
                    position.x + width/2 - diameter/4, position.y + diameter/4,
                    diameter/2, diameter/2);

     // Draw all the shapes
     g2D.setPaint(Color.BLACK);                                         // Draw in black
     g2D.draw(top);
     g2D.draw(bottom);

     g2D.setPaint(Color.BLUE);                                          // Draw in blue
     g2D.draw(circle1);
     g2D.draw(circle2);
     g2D.drawString("Arcs and ellipses", 80, 100);                      // Draw some text

   }

   private Sketcher theApp;                                             // The application object
 }

其他部分与上一例同。