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Technical Q&A QA1146

Illustrating document window changes in Swing

Q: I want to indicate that document windows have changed in my Java application. How can I draw the dot that appears in the window's close button, similar to Carbon and Cocoa applications?

Figure 1. Close buttons for windows with and without new/unsaved changes.

A: If you are using Swing with the Aqua look and feel under Java 1.3.1 for Mac OS X, there is a pure Java way of painting the modified indicator onto the close button. It is a simple Swing client property that can be set using the putClientProperty() method available to all subclasses of JComponent. The property is "windowModified", and needs to be set with a Boolean object for its value. This can be set directly on a JInternalFrame, or on the rootPane of a JFrame (JFrame extends the AWT Frame class and does not have clientProperty support). Listing 1 illustrates how this could be used in a text editor application:

import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;

public class Editor extends JFrame
  implements DocumentListener, ActionListener {

    final static String WINDOW_MODIFIED = "windowModified";

    JEditorPane jp;
    JMenuBar jmb;
    JMenu file;
    JMenuItem save;

    public Editor(String title) {
        super(title);
        jp = new JEditorPane();
        jp.getDocument().addDocumentListener(this);
        getContentPane().add(jp);
        jmb = new JMenuBar();
        file = new JMenu("File");
        save = new JMenuItem("Save");
        save.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_S,
          java.awt.Toolkit.getDefaultToolkit().getMenuShortcutKeyMask()));
        save.addActionListener(this);
        file.add(save);
        jmb.add(file);
        setJMenuBar(jmb);
        setSize(400,600);
        setVisible(true);
    }

    // doChange() and actionPerformed() handle the "windowModified" state
    public void doChange() {
        getRootPane().putClientProperty(WINDOW_MODIFIED, Boolean.TRUE);
    }

    public void actionPerformed(ActionEvent e) {
        // save functionality here...
        getRootPane().putClientProperty(WINDOW_MODIFIED, Boolean.FALSE);
    }

    // DocumentListener implementations
    public void changedUpdate(DocumentEvent e) { doChange(); }
    public void insertUpdate(DocumentEvent e)  { doChange(); }
    public void removeUpdate(DocumentEvent e)  { doChange(); }

    public static void main(String[] args) {
        new Editor("test");
    }
}

Listing 1. Text editor with "windowModified" status.

Technical Q&A QA1146 Illustrating document window changes in Swing

[Jun 18 2002]

Technical Q&A QA1146

Illustrating document window changes in Swing