scribbledemo.java

来自「此源码为机械工业出版社出版的《Java语言程序设计》第三版所配套的书中所有源代码」· Java 代码 · 共 102 行

// ScribbleDemo.java: Scribble using mouse
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class ScribbleDemo extends JApplet
{
  // This main method enables the applet to run as an application
  public static void main(String[] args)
  {
    // Create a frame
    JFrame frame = new JFrame("Scribbling Demo");

    // Create an instance of the applet
    ScribbleDemo applet = new ScribbleDemo();

    // Add the applet instance to the frame
    frame.getContentPane().add(applet, BorderLayout.CENTER);

    // Invoke init() and start()
    applet.init();
    applet.start();

    // Display the frame
    frame.setSize(300, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }

  // Initialize the applet
  public void init()
  {
    // Create a PaintPanel and add it to the applet
    getContentPane().add(new ScribblePanel(), BorderLayout.CENTER);
  }
}

// ScribblePanel for scribbling using the mouse
class ScribblePanel extends JPanel
  implements MouseListener, MouseMotionListener
{
  final int CIRCLESIZE = 20; // Circle diameter used for erasing
  private Point lineStart = new Point(0, 0); // Line start point
  private Graphics g; // Create a Graphics object for drawing

  public ScribblePanel()
  {
    // Register listener for the mouse event
    addMouseListener(this);
    addMouseMotionListener(this);
  }

  public void mouseClicked(MouseEvent e)
  {   
  }

  public void mouseEntered(MouseEvent e)
  {
  }

  public void mouseExited(MouseEvent e)
  {
  }

  public void mouseReleased(MouseEvent e)
  {
  }

  public void mousePressed(MouseEvent e)
  {
    lineStart.move(e.getX(), e.getY());
  }

  public void mouseDragged(MouseEvent e)
  {
    g = getGraphics(); // Get graphics context

    if (e.isMetaDown()) // Detect right button pressed
    {
      // Erase the drawing using an oval
      g.setColor(getBackground());
      g.fillOval(e.getX() - (CIRCLESIZE/2),
         e.getY() - (CIRCLESIZE/2), CIRCLESIZE, CIRCLESIZE);
    }
    else
    {
      g.setColor(Color.black);
      g.drawLine(lineStart.x, lineStart.y,
        e.getX(), e.getY());
    }

    lineStart.move(e.getX(), e.getY());

    // Dispose this graphics context
    g.dispose();
  }

  public void mouseMoved(MouseEvent e)
  {
  }
}