doodlepad.java

learning java的源代码。书中每个实例都有相关的代码example。

//file: DoodlePad.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class DoodlePad extends JFrame {

  public DoodlePad(  ) {
    super("DoodlePad");
    Container content = getContentPane(  );
    content.setLayout(new BorderLayout(  ));
    final DrawPad drawPad = new DrawPad(  );
    content.add(drawPad, BorderLayout.CENTER);
    JPanel p = new JPanel(  );
    JButton clearButton = new JButton("Clear");
    clearButton.addActionListener(new ActionListener(  ) {
      public void actionPerformed(ActionEvent e) {
        drawPad.clear(  );
      }
    });
    p.add(clearButton);
    content.add(p, BorderLayout.SOUTH);
    setSize(280, 300);
    setLocation(100, 100);
    addWindowListener(new WindowAdapter(  ) {
      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
    });
    setVisible(true);
  }

  public static void main(String[] args) {
    new DoodlePad(  );
  }
} // end of class DoodlePad

class DrawPad extends JComponent {
  Image image;
  Graphics2D graphics2D;
  int currentX, currentY, oldX, oldY;

  public DrawPad(  ) {
    setDoubleBuffered(false);
    addMouseListener(new MouseAdapter(  ) {
      public void mousePressed(MouseEvent e) {
        oldX = e.getX(  );
        oldY = e.getY(  );
      }
    });
    addMouseMotionListener(new MouseMotionAdapter(  ) {
      public void mouseDragged(MouseEvent e) {
        currentX = e.getX(  );
        currentY = e.getY(  );
        if (graphics2D != null)
          graphics2D.drawLine(oldX, oldY, currentX, currentY);
        repaint(  );
        oldX = currentX;
        oldY = currentY;
      }
    });
  }

  public void paintComponent(Graphics g) {
    if (image == null) {
      image = createImage(getSize().width, getSize(  ).height);
      graphics2D = (Graphics2D)image.getGraphics(  );
      graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
          RenderingHints.VALUE_ANTIALIAS_ON);
      clear(  );
    }
    g.drawImage(image, 0, 0, null);
  }

  public void clear(  ) {
    graphics2D.setPaint(Color.white);
    graphics2D.fillRect(0, 0, getSize().width, getSize(  ).height);
    graphics2D.setPaint(Color.black);
    repaint(  );
  }
}