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() と actionPerformed() で、windowModified の状態を扱う
    public void doChange() {
        getRootPane().putClientProperty(WINDOW_MODIFIED, Boolean.TRUE);
    }

    public void actionPerformed(ActionEvent e) {
        // ここで保存機能を記述する
        getRootPane().putClientProperty(WINDOW_MODIFIED, Boolean.FALSE);
    }

    // DocumentListener の実装
    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");
    }
}

リスト 1 windowModified の状態を含めたテキストエディタ