11.14 Look-and-Feel Preferences

A number of the examples in this chapter have used the utility class LookAndFeelPrefs to install the user's preferred look-and-feel and create a JMenu listing available look-and-feel choices. LookAndFeelPrefs is shown in Example 11-29. It demonstrates the use of the javax.swing.UIManager class for querying and setting look-and-feels, and also demonstrates the use of the java.util.prefs package (new in Java 1.4) for retrieving and storing persistent user preferences.

LookAndFeelPrefs relies on the list of installed look-and-feel implementations returned by UIManager.getInstalledLookAndFeels( ). By default (in Java 1.4.2, at least) this method returns three look-and-feels: the Java "Metal" look-and-feel, the Motif (CDE) look-and-feel, and the Windows look-and-feel. This is true even on non-Windows platforms for which the Windows look-and-feel is unsupported. Java 1.4.2 also ships with a GTK look-and-feel, which mimics the Linux GTK look-and-feel, but getInstalledLookAndFeels( ) does not know about it. To make this new look-and-feel available to the LookAndFeelPrefs example, you'll need to create a swing.properties file and place it in the jre/lib/ directory of your Java SDK. The contents of the file should look like this:

# Add the Mac look-and-feel if your SDK comes with it. # Delete the Windows look-and-feel if it is not supported on your platform. swing.installedlafs = gtk,metal,motif,win swing.installedlaf.gtk.name = GTK Look and Feel, swing.installedlaf.gtk.class = com.sun.java.swing.plaf.gtk.GTKLookAndFeel swing.installedlaf.metal.name = Java Look and Feel swing.installedlaf.metal.class = javax.swing.plaf.metal.MetalLookAndFeel swing.installedlaf.motif.name = Motif/CDE Look and Feel swing.installedlaf.motif.class = com.sun.java.swing.plaf.motif.MotifLookAndFeel swing.installedlaf.win.name = Windows Look and Feel swing.installedlaf.win.class = com.sun.java.swing.plaf.windows.WindowsLookAndFeel

Example 11-29. LookAndFeelPrefs.java

package je3.gui; import javax.swing.*; import java.awt.event.*; import java.util.prefs.Preferences; public class LookAndFeelPrefs {     public static final String PREF_NAME = "preferredLookAndFeelClassName";     /**      * Get the desired look-and-feel from a per-user preference.  If      * the preference doesn't exist or is unavailable, use the      * default look-and-feel.  The preference is shared by all classes      * in the same package as prefsClass.      **/     public static void setPreferredLookAndFeel(Class prefsClass) {         Preferences prefs=Preferences.userNodeForPackage(prefsClass);         String defaultLAF = UIManager.getSystemLookAndFeelClassName( );         String laf = prefs.get(PREF_NAME, defaultLAF);         try { UIManager.setLookAndFeel(laf); }         catch (Exception e) { // ClassNotFound or InstantiationException             // An exception here is probably caused by a bogus preference.             // Ignore it silently; the user will make do with the default LAF.         }     }     /**      * Create a menu of radio buttons listing the available Look and Feels.      * When the user selects one, change the component hierarchy under frame      * to the new LAF, and store the new selection as the current preference      * for the package containing class c.      **/     public static JMenu createLookAndFeelMenu(final Class prefsClass,                                               final ActionListener listener)     {         // Create the menu         final JMenu plafmenu = new JMenu("Look and Feel");         // Create an object used for radio button mutual exclusion         ButtonGroup radiogroup = new ButtonGroup( );           // Look up the available look-and-feels         UIManager.LookAndFeelInfo[  ] plafs=UIManager.getInstalledLookAndFeels( );         // Find out which one is currently used         String currentLAFName=UIManager.getLookAndFeel( ).getClass( ).getName( );         // Loop through the plafs, and add a menu item for each one         for(int i = 0; i < plafs.length; i++) {             String plafName = plafs[i].getName( );             final String plafClassName = plafs[i].getClassName( );             // Create the menu item             final JMenuItem item =                 plafmenu.add(new JRadioButtonMenuItem(plafName));             item.setSelected(plafClassName.equals(currentLAFName));                          // Tell the menu item what to do when it is selected             item.addActionListener(new ActionListener( ) {                 public void actionPerformed(ActionEvent event) {                     // Set the new look-and-feel                     try { UIManager.setLookAndFeel(plafClassName); }                     catch(UnsupportedLookAndFeelException e) {                         // Sometimes a Look-and-Feel is installed but not                         // supported, as in the Windows LaF on Linux platforms.                         JOptionPane.showMessageDialog(plafmenu,                               "The selected Look-and-Feel is " +                               "not supported on this platform.",                               "Unsupported Look And Feel",                               JOptionPane.ERROR_MESSAGE);                         item.setEnabled(false);                     }                     catch (Exception e) { // ClassNotFound or Instantiation                         item.setEnabled(false);  // shouldn't happen                     }                     // Make the selection persistent by storing it in prefs.                     Preferences p = Preferences.userNodeForPackage(prefsClass);                     p.put(PREF_NAME, plafClassName);                     // Invoke the supplied action listener so the calling                     // application can update its components to the new LAF                     // Reuse the event that was passed here.                     listener.actionPerformed(event);                 }             });             // Only allow one menu item to be selected at once             radiogroup.add(item);           }         return plafmenu;     } }