JFrame实现透明效果

例子：

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowFocusListener;

import javax.swing.*;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.UIManager;

import org.jvnet.substance.SubstanceLookAndFeel;
import org.jvnet.substance.theme.SubstanceLightAquaTheme;

public class TestEvent extends JComponent implements ComponentListener,
  WindowFocusListener {
 private JFrame frame;

 private Boolean isHiding = false, isShowing = false, start = false;

 private Image background;

 private Point p;

 // 获得当前屏幕快照
 public void updateBackground() {
  try {
   Robot rbt = new Robot();
   Toolkit tk = Toolkit.getDefaultToolkit();
   Dimension dim = tk.getScreenSize();
   background = rbt.createScreenCapture(new Rectangle(0, 0, (int) dim
     .getWidth(), (int) dim.getHeight()));
  } catch (Exception ex) {
  }
 }
 // 将窗口掉离出屏幕以获得纯粹的背景图象
 public void refresh() {
  if (start == true) {
   this.updateBackground();
   frame.setLocation(p);
   if (p.x < 0 || p.y < 0)
    frame.setLocation(0, 0);
   this.repaint();
  }
 }

 public void componentHidden(ComponentEvent e) {
  // TODO Auto-generated method stub
  System.out.println("Hidden");
 }

 // 窗口移动时
 public void componentMoved(ComponentEvent e) {
  // TODO Auto-generated method stub
  System.out.println("moved");
  this.repaint();
 }

 // 窗口改变大小时
 public void componentResized(ComponentEvent e) {
  // TODO Auto-generated method stub
  System.out.println("resized");
  this.repaint();
 }

 public void componentShown(ComponentEvent e) {
  // TODO Auto-generated method stub
  System.out.println("shown");
 }

 // 窗口得到焦点后,用refresh()方法更新界面
 public void windowGainedFocus(WindowEvent e) {
  // TODO Auto-generated method stub
  System.out.println("gainedFocus");
  refresh();
  start = false;
 }

 // 窗口失去焦点后,将其移出屏幕
 public void windowLostFocus(WindowEvent e) {
  // TODO Auto-generated method stub
  System.out.println("lostFocus");
  if (frame.isShowing() == true) {
   System.out.println("visible");
  } else {
   System.out.println("invisible");
  }
  start = true;
  p = frame.getLocation();
  frame.setLocation(-2000, -2000);
 }

 public TestEvent(JFrame frame) {
  super();
  this.frame = frame;
  updateBackground();
  this.setSize(200, 120);
  this.setVisible(true);
  frame.addComponentListener(this);
  frame.addWindowFocusListener(this);

  // TODO Auto-generated constructor stub
 }

 // 绘制外观,注意,其中 pos,offset 是为了将特定部分的图象贴到窗口上
 public void paintComponent(Graphics g) {
  Point pos = this.getLocationOnScreen();
  Point offset = new Point(-pos.x, -pos.y);
  g.drawImage(background, offset.x, offset.y, null);
 }

 /**
  * @param args
  */
 public static void main(String[] args) {
  try {
   UIManager.setLookAndFeel(new SubstanceLookAndFeel());
   UIManager.put("swing.boldMetal", false);
   if (System.getProperty("substancelaf.useDecorations") == null) {
    JFrame.setDefaultLookAndFeelDecorated(true);
   }
   System.setProperty("sun.awt.noerasebackground", "true");
   SubstanceLookAndFeel.setCurrentTheme(new SubstanceLightAquaTheme());
  } catch (Exception e) {
   System.err.println("Oops!  Something went wrong!");
  }

  JFrame frame = new JFrame("Transparent Window");
  ((JPanel)frame.getContentPane()).setOpaque(true);
  TestEvent t = new TestEvent(frame);
  t.setLayout(new BorderLayout());
  JButton button = new JButton("This is a button");
  t.add("North", button);
  JLabel label = new JLabel("This is a label");
  t.add("South", label);
  frame.getContentPane().add("Center", t);
  frame.pack();
  frame.setSize(150, 100);
  frame.show();
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 }

}