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。