《Java2图形设计卷II：Swing》配套光盘源码

				import javax.swing.*;
				import java.awt.*;
				import java.awt.event.*;
				import java.util.*;
				
				public class Test extends JApplet {
					public void init() {
						Container contentPane = getContentPane();
						JMenuBar menuBar = new JMenuBar();
						JMenu fileMenu = new JMenu("File");
				
						fileMenu.add(new UnderlineElement("item one"));
						fileMenu.add(new UnderlineElement("item two"));
						fileMenu.add(new UnderlineElement("item three"));
				
						menuBar.add(fileMenu);
						setJMenuBar(menuBar);
					}
				}
				class UnderlineElement extends JButton implements MenuElement {
					private boolean drawUnderline = false;
				
					public UnderlineElement(String s) {
						super(s);
						setBorder(BorderFactory.createEmptyBorder(2,2,2,2));
					}
					public Component getComponent() {
						return this;
					}
					public MenuElement[] getSubElements() {
						return new MenuElement[0];
					}
					public void menuSelectionChanged(boolean b) {
						drawUnderline = b;
						repaint();
					}
					public void paintComponent(Graphics g) {
						super.paintComponent(g);
				
						Insets insets = getInsets();
				
						if(drawUnderline) {
							FontMetrics fm = g.getFontMetrics();
							g.drawLine(insets.left, insets.top + fm.getHeight(),
									fm.stringWidth(getText()), 
									insets.top + fm.getHeight());
						}
					}
					public void processKeyEvent(KeyEvent me,
												MenuElement[] element, 
												MenuSelectionManager msm) {
					}
				    public void processMouseEvent(MouseEvent me) {
						super.processMouseEvent(me);
						MenuSelectionManager.defaultManager().processMouseEvent(
																			  me);
				    }
					public void processMouseEvent(MouseEvent me, 
												MenuElement[] element, 
												MenuSelectionManager msm) {
						if(me.getID() == MouseEvent.MOUSE_CLICKED || 
						   me.getID() == MouseEvent.MOUSE_RELEASED) {
				
							msm.setSelectedPath(null);
							doClick();
						}
						else
							msm.setSelectedPath(getPath());
					}
				    public MenuElement[] getPath() {
						MenuSelectionManager defaultManager = 
						MenuSelectionManager.defaultManager();
						MenuElement oldPath[] = defaultManager.getSelectedPath();
						MenuElement newPath[];
						int len = oldPath.length;
				
						if(len > 0) {
							MenuElement lastElement = oldPath[len-1];
							Component parent = getParent();
				
							if (lastElement == parent) {
								newPath = new MenuElement[len+1];
				
								System.arraycopy(oldPath, 0, newPath, 0, len);
								newPath[len] = this;
							}
							else {
								int j;
				
								for (j = len-1; j >= 0; j--) {
									if (oldPath[j].getComponent() == parent)
										break;
								}
								newPath = new MenuElement[j+2];
								System.arraycopy(oldPath, 0, newPath, 0, j+1);
								newPath[j+1] = this;
							}
						}
						else
							return new MenuElement[0];
				
						return newPath;
					}
				}