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Java Tip 72: Press Escape to close your Swing dialog windows

Discover how to program keystroke responses in your Dialogs' parent classes

By John Zukowski, JavaWorld.com, 04/01/99

Since the JFC/Swing dialog window is a subclass of the AWT dialog window, theoretically you could simply change the class subclassed by the earlier EscapeDialog. Instead of subclassing the AWT dialog window, the EscapeDialog could subclass the JFC/Swing JDialog window. For all practical purposes, recursively adding key listeners would work, causing the Escape key to close the JFC/Swing dialog window.

While the change of parent classes from the Dialog to JDialog would work, the JFC/Swing component library offers a much simpler approach. The JComponent class defines a couple of registerKeyboardAction() methods for just this type of behavior:

public void registerKeyboardAction(ActionListener action, KeyStroke keyStroke, int condition);
public void registerKeyboardAction(ActionListener action, String command, KeyStroke keyStroke, int condition);

All you need to do is to create a custom subclass of JDialog, define an ActionListener for closing the JDialog, and register the Escape keystroke to call the action listener. Then, when the user presses the Escape key when the JDialog is open, JDialog automatically goes away.

Here's a closer look at those three steps:

Step 1. Subclass JDialog

public class EscapeDialog extends JDialog {
  ...
}

Step 2. Define the ActionListener

ActionListener actionListener = new ActionListener() {
  public void actionPerformed(ActionEvent actionEvent) {
     setVisible(false);
  }
};

Step 3. Define and register the keystroke

Since the registerKeyboardAction() method is part of the JComponent class definition, you must define the Escape keystroke and register the keyboard action with a JComponent, not with a JDialog. The JRootPane for the JDialog serves as an excellent choice to associate the registration, as this will always be visible. If you override the protected createRootPane() method of JDialog, you can return your custom JRootPane with the keystroke enabled:

protected JRootPane createRootPane() {
  KeyStroke stroke = KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0);
  JRootPane rootPane = new JRootPane();
  rootPane.registerKeyboardAction(actionListener, stroke, JComponent.WHEN_IN_FOCUSED_WINDOW);
  return rootPane;
}

Technically speaking, that's all there is to it with the JFC/Swing JDialog window. You can then create and use the new-and-improved EscapeDialog window in all your JFC/Swing-based applications just as you would a JDialog. From a useability perspective, you may wish to replicate the many constructors of JDialog. The accompanying source code (EscapeDialog.java) provides a common set of nine constructors, as offered by the original JDialog class. In addition, the SetupEscapeFrame.java file demonstrates its usage.