In Jskad, you can now clear the preferences and return to default values.

source/org/thdl/tib/input/Jskad.java

@@ -121,9 +121,14 @@ public class Jskad extends JPanel implements DocumentListener {
     private Jskad(LayoutManager lm, boolean isDB) { super(lm, isDB); }
 
     /** Saves user preferences to disk if possible. */
-    private static void savePreferencesAction() {
+    private void savePreferencesAction() {
         try {
-            ThdlOptions.saveUserPreferences();
+            if (!ThdlOptions.saveUserPreferences()) {
+                JOptionPane.showMessageDialog(Jskad.this,
+                                              "You previously cleared preferences,\nso you cannot now save them.",
+                                              "Cannot Save User Preferences",
+                                              JOptionPane.PLAIN_MESSAGE);
+            }
         } catch (IOException ioe) {
             System.out.println("IO Exception saving user preferences to " + ThdlOptions.getUserPreferencesPath());
             ioe.printStackTrace();
@@ -131,6 +136,22 @@ public class Jskad extends JPanel implements DocumentListener {
         }
     }
 
+    /** Clears user preferences by deleting the preferences file on
+        disk.  Prompts the user to quit and reopen Jskad. */
+    private void clearPreferencesAction() {
+        try {
+            ThdlOptions.clearUserPreferences();
+        } catch (IOException ioe) {
+            System.out.println("IO Exception deleting user preferences file " + ThdlOptions.getUserPreferencesPath());
+            ioe.printStackTrace();
+            ThdlDebug.noteIffyCode();
+        }
+        JOptionPane.showMessageDialog(Jskad.this,
+                                      "You must now exit this application and restart\nbefore default preferences will take effect.",
+                                      "Clearing Preferences",
+                                      JOptionPane.PLAIN_MESSAGE);
+    }
+
     /** pane displaying Jskad's single HTML help file */
     private static HTMLPane helpPane;
 
@@ -294,6 +315,17 @@ public class Jskad extends JPanel implements DocumentListener {
             editMenu.add(preferencesItem);
         }
 
+        {
+            JMenuItem preferencesItem = new JMenuItem("Clear preferences");
+            preferencesItem.addActionListener(new ThdlActionListener() {
+                    public void theRealActionPerformed(ActionEvent e) {
+                        clearPreferencesAction();
+                    }
+                });
+            editMenu.addSeparator();
+            editMenu.add(preferencesItem);
+        }
+
         menuBar.add(editMenu);
 
 		JMenu toolsMenu = new JMenu("Tools");
@@ -1172,7 +1204,8 @@ public class Jskad extends JPanel implements DocumentListener {
             y_size = d.height/4*3;
             f.setSize(x_size, y_size);
             f.setLocation(d.width/8, d.height/8);
-            f.getContentPane().add(new Jskad(f));
+            final Jskad jskad = new Jskad(f);
+            f.getContentPane().add(jskad);
             f.setVisible(true);
 
             /* Make it so that any time the user exits Jskad by
@@ -1181,7 +1214,7 @@ public class Jskad extends JPanel implements DocumentListener {
              * correct. */
             Runtime.getRuntime().addShutdownHook(new Thread() {
                     public void run() {
-                        savePreferencesAction();
+                        jskad.savePreferencesAction();
                     }
                 }
                                                 );

source/org/thdl/util/ThdlOptions.java

@@ -372,12 +372,40 @@ public final class ThdlOptions {
         }
     }
 
+    /** Deletes the user's preferences file, a file whose path is the
+     *  value of {@link #getUserPreferencesPath()}.  You must restart
+     *  the application before this will take effect.
+     *
+     *  @throws IOException if an IO or security exception occurs
+     *  while deleting from disk. */
+    public static void clearUserPreferences() throws IOException {
+        // Avoid saving the preferences to disk at program exit.  Do
+        // this first in case an exception is thrown during deletion.
+        userProperties = null;
+
+        File pf = new File(getUserPreferencesPath());
+
+        try {
+            if (pf.exists() && !pf.delete()) {
+                throw new IOException("Could not delete the preferences file "
+                                      + pf.getAbsolutePath());
+            }
+        } catch (SecurityException e) {
+            throw new IOException("Could not delete the preferences file because a SecurityManager is in place and your security policy does not allow deleting "
+                                  + pf.getAbsolutePath());
+        }
+    }
+
     /** Saves the user's preferences to a file whose path is the value
      *  of {@link #getUserPreferencesPath()}.  You must call
      *  <code>setUserPreference(..)</code> for this to be effective.
+     *
+     *  @return true on success, false if no preferences exist to be
+     *  saved, such as after calling clearUserPreferences()
+     *
      *  @throws IOException if an IO exception occurs while writing to
      *  the disk. */
-    public static void saveUserPreferences() throws IOException {
+    public static boolean saveUserPreferences() throws IOException {
         if (null != userProperties) {
             userProperties.store(new FileOutputStream(getUserPreferencesPath()),
                                  " This file was automatically created by a THDL tool.\n"
@@ -400,7 +428,9 @@ public final class ThdlOptions {
                                  + "# preferences mechanism at this time.  Yell for it!\n"
                                  + "# \n"
                                  + "# Created at:"); // DLC FIXME: document the preferences mechanism.
+            return true;
         }
+        return false;
     }
 
     /** This returns the location of the user's preferences file.