Java 制作的一个放大镜程序

package com.mocake.jna;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Magnifier extends JFrame {
 /**
  * 主容器
  */
 private Container container = getContentPane();

 /**
  * 放大镜x坐标
  * 计算方式：setCoordinateX = absoluteCoordinateX 
  * - relativeCoordinateXWhenMousePressed
  */
 private int setCoordinateX;

 /**
  * 放大镜y坐标
  * 计算方式：setCoordinateY = absoluteCoordinateY 
  * - relativeCoordinateYWhenMousePressed
  */
 private int setCoordinateY;

 /**
  * 鼠标绝对x坐标
  */
 private int absoluteCoordinateX;

 /**
  * 鼠标绝对y坐标
  */
 private int absoluteCoordinateY;

 /**
  * 鼠标按下时的相对x坐标
  */
 private int relativeCoordinateXWhenMousePressed;

 /**
  * 鼠标按下时的相对y坐标
  */
 private int relativeCoordinateYWhenMousePressed;

 /**
  * 标记鼠标是否按下。如果按下则为true，否则为false
  */
 private boolean mousePressedNow;

 /**
  * 放大镜尺寸
  */
 private int magnifierSize = 100;

 /**
  * 放大镜内容面板
  */
 private MagnifierPanel magnifierPanel = new MagnifierPanel(magnifierSize);

 /**
  * 构造函数，创建一个放大镜窗体
  */
 public Magnifier() {
  setUndecorated(true); // 窗体边缘
  setResizable(false);
  container.add(magnifierPanel);
  addMouseListener(new MouseFunctions());
  addMouseMotionListener(new MouseMotionFunctions());
  updateSize(magnifierSize);
  this.setVisible(true);
 }

 /**
  * 程序入口点
  * 
  * @param arg
  *                启动参数，这里为空
  */
 public static void main(String arg[]) {
  Magnifier magnifier = new Magnifier();
  magnifier.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 }

 /**
  * 更新窗体
  * 
  * @param magnifierSize
  *                放大镜尺寸
  */
 public void updateSize(int magnifierSize) {
  magnifierPanel.setMagnifierSize(magnifierSize + 100);
  setSize(magnifierSize + 100, magnifierSize + 100);
  validate(); // 更新所有子控件
 }

 private class MouseFunctions extends MouseAdapter {
  public void mousePressed(MouseEvent e) {
   if (e.getClickCount() == 1) {// 如果鼠标左键点了一下，说明按住了窗体
    mousePressedNow = true;
    relativeCoordinateXWhenMousePressed = e.getX();
    relativeCoordinateYWhenMousePressed = e.getY();
   }
  }

  public void mouseReleased(MouseEvent e) {
   mousePressedNow = false;
  }
 }

 private class MouseMotionFunctions extends MouseMotionAdapter {
  public void mouseDragged(MouseEvent e) {
   if (mousePressedNow == true) {// 如果此时鼠标按下了，说明在拖拽窗体
    absoluteCoordinateX = Magnifier.this.getLocationOnScreen().x
      + e.getX();
    absoluteCoordinateY = Magnifier.this.getLocationOnScreen().y
      + e.getY();
    setCoordinateX = absoluteCoordinateX
      - relativeCoordinateXWhenMousePressed;
    setCoordinateY = absoluteCoordinateY
      - relativeCoordinateYWhenMousePressed;
    magnifierPanel.setMagnifierLocation(setCoordinateX,
      setCoordinateY);
    setLocation(setCoordinateX, setCoordinateY);
   }
  }
 }
}

class MagnifierPanel extends JPanel {
 private Image screenImage;

 /**
  * 放大镜的尺寸
  */
 private int magnifierSize;

 private int locationX;

 private int locationY;

 private Robot robot;

 /**
  * 带参数的构造函数
  * @param magnifierSize
  *         放大尺寸
  */
 public MagnifierPanel(int magnifierSize) {
  try {
   robot = new Robot();
  } catch (AWTException e) {
  }
  // 截屏幕
  screenImage = robot.createScreenCapture(new Rectangle(0, 0, Toolkit
    .getDefaultToolkit().getScreenSize().width, Toolkit
    .getDefaultToolkit().getScreenSize().height));
  this.magnifierSize = magnifierSize;
 }

 /**
  * 设置放大镜的位置
  * @param locationX
  *         x坐标
  * @param locationY
  *         y坐标
  */
 public void setMagnifierLocation(int locationX, int locationY) {
  this.locationX = locationX;
  this.locationY = locationY;
  repaint(); // 注意重画控件
 }

 /**
  * 设置放大镜的尺寸
  * @param magnifierSize
  *         放大镜尺寸
  */
 public void setMagnifierSize(int magnifierSize) {
  this.magnifierSize = magnifierSize;
 }

 public void paintComponent(Graphics g) {
  super.paintComponent((Graphics2D) g);
  // 关键处理代码
  g.drawImage(screenImage, // 要画的图片
    0, // 目标矩形的第一个角的x坐标     
    0, // 目标矩形的第一个角的y坐标
    magnifierSize, // 目标矩形的第二个角的x坐标
    magnifierSize, // 目标矩形的第二个角的y坐标
    locationX + (magnifierSize / 4), // 源矩形的第一个角的x坐标
    locationY + (magnifierSize / 4), // 源矩形的第一个角的y坐标
    locationX + (magnifierSize / 4 * 3), // 源矩形的第二个角的x坐标
    locationY + (magnifierSize / 4 * 3), // 源矩形的第二个角的y坐标
    this);
 }
}