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

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
}