Java基础之在窗口中绘图——绘制直线和矩形（Sketcher 2 drawing lines and rectangles）

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

g2D.setPaint(Color.RED);                                           // Draw in red

// Position width and height of first rectangle
Point2D.Float p1 = new Point2D.Float(50.0f, 10.0f);
float width1 = 60;
float height1 = 80;

// Create and draw the first rectangle
Rectangle2D.Float rect = new Rectangle2D.Float(p1.x, p1.y, width1, height1);
g2D.draw(rect);

// Position width and height of second rectangle
Point2D.Float p2 = new Point2D.Float(150.0f, 100.0f);
float width2 = width1 + 30;
float height2 = height1 + 40;

// Create and draw the second rectangle
g2D.draw(new Rectangle2D.Float(
(float)(p2.getX()), (float)(p2.getY()), width2, height2));
g2D.setPaint(Color.BLUE);                                          // Draw in blue

// Draw lines to join corresponding corners of the rectangles
Line2D.Float line = new Line2D.Float(p1,p2);
g2D.draw(line);

p1.setLocation(p1.x + width1, p1.y);
p2.setLocation(p2.x + width2, p2.y);
g2D.draw(new Line2D.Float(p1,p2));

p1.setLocation(p1.x, p1.y + height1);
p2.setLocation(p2.x, p2.y + height2);
g2D.draw(new Line2D.Float(p1,p2));

p1.setLocation(p1.x - width1, p1.y);
p2.setLocation(p2.x - width2, p2.y);
g2D.draw(new Line2D.Float(p1, p2));

g2D.drawString("Lines and rectangles", 60, 250);                   // Draw some text

}

private Sketcher theApp;                                             // The application object
}