Help tips in Swing?

I’m sure there are many developers who would like to provide this spiffy functionality, so if you could provide a way of doing this I’m sure you’d make a lot of people happy.

I’m using JDK 1.2.2 FCS.

A: The Java Q&A experts recommend that, instead of using inheritance, you use delegation to create a generic adapter class in order to achieve your desired functionality.

This adapter class will take a JMenuItem, a string of help text to display, and a JLabel to be the status bar in which to display the message. When a menu item is activated, the adapter will cause the appropriate text to display in the status bar.

The difficult aspect of your problem: how to figure out what event to listen for? It turns out that a ChangeEvent is generated when menu items activate and deactivate. Java’s term for this is arming the menu item. Using this information, the following adapter class can be written:

class MenuHelpTextAdapter implements ChangeListener
{
   private JMenuItem menuItem;
   private String helpText;
   private JLabel statusBar;
   public MenuHelpTextAdapter(JMenuItem menuItem, String helpText, JLabel statusBar)
   {
      this.menuItem = menuItem;
      this.helpText = helpText;
      this.statusBar = statusBar;
      menuItem.addChangeListener(this);
   }
   public void stateChanged(ChangeEvent evt)
   {
      if (menuItem.isArmed())
         statusBar.setText(helpText);
      else
         statusBar.setText(" ");
   }
}

The code that creates the adapters for the menu items is quite simple:

   new MenuHelpTextAdapter(item1, "Help text for item 1", statusBar);
   new MenuHelpTextAdapter(item2, "Item 2 info", statusBar);

Using this adapter — as an inner class in this case — we can create a complete sample program:

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
public class StatusBarTest
{
   JLabel statusBar;
   JMenuItem item1;
   JMenuItem item2;
   private void init()
   {
      JFrame frame = new JFrame("Status Bar Test");
      JMenuBar menuBar = new JMenuBar();
      frame.setJMenuBar(menuBar);
      JMenu fileMenu = new JMenu("File");
      menuBar.add(fileMenu);
      item1 = new JMenuItem("Item 1");
      item2 = new JMenuItem("Item 2");
      fileMenu.add(item1);
      fileMenu.add(item2);
      Container contentPane = frame.getContentPane();
      contentPane.setLayout(new BorderLayout());
      contentPane.add("Center", new JButton("Main application area"));
      statusBar = new JLabel(" ");
      contentPane.add("South", statusBar);
      new MenuHelpTextAdapter(item1, "Help text for item 1", statusBar);
      new MenuHelpTextAdapter(item2, "Item 2 info", statusBar);
      frame.setSize(400,400);
      frame.setVisible(true);
   }
   public static void main(String[] args)
   {
      StatusBarTest t = new StatusBarTest();
      t.init();
   }
   class MenuHelpTextAdapter implements ChangeListener
   {
      private JMenuItem menuItem;
      private String helpText;
      private JLabel statusBar;
       public MenuHelpTextAdapter(JMenuItem menuItem, String helpText,
       JLabel statusBar)
     {
         this.menuItem = menuItem;
         this.helpText = helpText;
         this.statusBar = statusBar;
         menuItem.addChangeListener(this);
      }
      public void stateChanged(ChangeEvent evt)
      {
         if (menuItem.isArmed())
            statusBar.setText(helpText);
         else
            statusBar.setText(" ");
      }
   }
}