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