在Windows的“开始”菜单上，会在菜单左侧显示一幅图像。很多基于Windows的软件也有类似效果的菜单。用Java Swing可以制作出类似效果的菜单吗？答案当然是肯定的，而且非常简单。
我们首先从Swing的JPopupMenu组件进行扩展，让其接受一个图片，显示在左侧；或者接受一个字符串，动态生成图片后，在显示在左侧。为了避免准备图片的麻烦，我们就以动态生成内存图片为例，编写一个JImagedPopupMenu类。
JImagedPopupMenu在创建时可以接受一个字符串，生成一副内存图片BufferedImage。然后，我们需要覆盖JComponent的getInsets方法，重新计算Inset的left值，将其在原数值基础上加上图片的宽度，然后返回：
?public Insets getInsets() {
??????? Insets insets = (Insets)super.getInsets().clone();
??????? insets.left += imageIcon.getIconWidth();
??????? return insets;
??? }
最后，覆盖paintComponent方法，在原基础上增加图片的绘制：
??? public void paintComponent(Graphics g) {
??????? super.paintComponent(g);
??????? if (imageIcon != null) {
??????????? Insets insets = getInsets();
??????????? g.drawImage(imageIcon.getImage(),
??????????????????????? insets.left - imageIcon.getIconWidth(),
??????????????????????? insets.top,
??????????????????????? null);
??????? }
??? }
完整代码如下：
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.*;
import javax.swing.*;
public class ImageMenu extends JPopupMenu {
??? private Font font = new Font("Dialog", Font.BOLD, 13);
??? private ImageIcon imageIcon = null;
??? public ImageMenu(ImageIcon imageIcon) {
??????? this.imageIcon = imageIcon;
??? }
??? public ImageMenu(String text) {
??????? this.imageIcon = createImage(text);
??? }
??? private ImageIcon createImage(String text) {
??????? BufferedImage bi = new BufferedImage(30, 1000, BufferedImage.TYPE_INT_ARGB);
??????? ImageIcon image = new ImageIcon(bi);
??????? Graphics2D g2d = bi.createGraphics();
??????? GradientPaint paint = new GradientPaint(0, 0, Color.yellow, 30, 10, Color.red, true);
??????? g2d.setPaint(paint);
??????? g2d.fillRect(0, 0, bi.getWidth(), bi.getHeight());
??????? AffineTransform at = new AffineTransform();
??????? at.rotate( -Math.PI / 2);
??????? g2d.setTransform(at);
??????? g2d.setColor(Color.white);
??????? g2d.setFont(font);
??????? g2d.drawString(text, -180, bi.getWidth() / 2);
??????? return image;
??? }
??? public Insets getInsets() {
??????? Insets insets = (Insets)super.getInsets().clone();
??????? insets.left += imageIcon.getIconWidth();
??????? return insets;
??? }
??? public void paint(Graphics g) {
??????? super.paint(g);
??????? if (imageIcon != null) {
??????????? Insets insets = getInsets();
??????????? g.drawImage(imageIcon.getImage(),
??????????????????????? insets.left - imageIcon.getIconWidth(),
??????????????????????? insets.top,
??????????????????????? null);
??????? }
??? }
??? public static void main(String[] args) {
??????? final JFrame frame = new JFrame();
??????? frame.setSize(600, 500);
??????? frame.setTitle("ImageMenu");
??????? final ImageMenu menu = new ImageMenu("Windows XP Perfessional");
??????? menu.add(new JMenuItem("Winzip 8.0"));
??????? menu.addSeparator();
??????? menu.add(new JMenuItem("Programs"));
??????? menu.add(new JMenuItem("Document"));
??????? menu.add(new JMenuItem("Settings"));
??????? menu.add(new JMenuItem("Search"));
??????? menu.add(new JMenuItem("Help and Support"));
??????? menu.add(new JMenuItem("Run..."));
??????? menu.addSeparator();
??????? menu.add(new JMenuItem("Shut Down..."));
??????? JLabel label = new JLabel("Right click me to show image popup menu.");
??????? label.addMouseListener(new java.awt.event.MouseAdapter() {
??????????? public void mouseReleased(MouseEvent e) {
??????????????? if (e.isPopupTrigger()) {
??????????????????? menu.show(frame, e.getPoint().x, e.getPoint().y);
??????????????? }
??????????? }
??????? });
??????? frame.getContentPane().add(label, BorderLayout.CENTER);
??????? frame.show();
??? }
}
同样，采用这种方法，也可以将JMenu扩展出同样的效果。
