Java Foundation Classes in a Nutshell

Example 3−1: Cr eating Pull-Down and Pop-Up Menus in Swing (continued)

// A convenience method for creating radio button menu items

public static JMenuItem radioItem(String label, ActionListener listener,

String command, ButtonGroup mutExGroup) {

JMenuItem item = new JRadioButtonMenuItem(label);

item.addActionListener(listener);

item.setActionCommand(command);

mutExGroup.add(item);

return item;

}

// An event listener class used with the menu items created above

// For this demo, it just displays a dialog box when an item is selected

public static class MenuItemActionListener implements ActionListener {

Component parent;

public MenuItemActionListener(Component parent) { this.parent = parent; }

public void actionPerformed(ActionEvent e) {

JMenuItem item = (JMenuItem) e.getSource();

String cmd = item.getActionCommand();

JOptionPane.showMessageDialog(parent, cmd + " was selected.");

}

}

}

JTree and TreeModel

The javax.swing.JTree class is a powerful Swing component for displaying tree-

structur ed data. Like all Swing components,

JTree relies on a separate model

object to hold and repr esent the data that it displays. Most Swing components cre-

ate this model object automatically, and you never need to work with it explicitly.

The

JTree component, however, displays data that is much more complex than a

typical Swing component. When you are working with a

JTree, you must create a

model object that implements the ...