diff --git a/src/java/davmail/ui/AboutFrame.java b/src/java/davmail/ui/AboutFrame.java
index 14086126..5da40a56 100644
--- a/src/java/davmail/ui/AboutFrame.java
+++ b/src/java/davmail/ui/AboutFrame.java
@@ -35,7 +35,7 @@ public class AboutFrame extends JFrame {
             imageLabel.setIcon(icon);
             JPanel imagePanel = new JPanel();
             imagePanel.add(imageLabel);
-            add("West", imagePanel);
+            add(BorderLayout.WEST, imagePanel);
         } catch (IOException e) {
             DavGatewayTray.error("Unable to create icon", e);
         }
@@ -66,7 +66,7 @@ public class AboutFrame extends JFrame {
 
         JPanel mainPanel = new JPanel();
         mainPanel.add(jEditorPane);
-        add("Center", mainPanel);
+        add(BorderLayout.CENTER, mainPanel);
 
         JPanel buttonPanel = new JPanel();
         JButton ok = new JButton("OK");
@@ -79,7 +79,7 @@ public class AboutFrame extends JFrame {
 
         buttonPanel.add(ok);
 
-        add("South", buttonPanel);
+        add(BorderLayout.SOUTH, buttonPanel);
 
         pack();
         setResizable(false);
diff --git a/src/java/davmail/ui/AcceptCertificateDialog.java b/src/java/davmail/ui/AcceptCertificateDialog.java
index 0672855d..e2292cb0 100644
--- a/src/java/davmail/ui/AcceptCertificateDialog.java
+++ b/src/java/davmail/ui/AcceptCertificateDialog.java
@@ -10,7 +10,9 @@ import java.awt.event.ActionListener;
 import java.lang.reflect.InvocationTargetException;
 import java.security.cert.X509Certificate;
 import java.text.SimpleDateFormat;
+import java.text.DateFormat;
 import java.util.Date;
+import java.util.Locale;
 
 /**
  * Accept certificate dialog
@@ -36,7 +38,7 @@ public class AcceptCertificateDialog extends JDialog {
     public AcceptCertificateDialog(X509Certificate certificate) {
         setAlwaysOnTop(true);
         String sha1Hash = DavGatewayX509TrustManager.getFormattedHash(certificate);
-        SimpleDateFormat formatter = new SimpleDateFormat("MM/dd/yyyy");
+        DateFormat formatter = DateFormat.getDateInstance(DateFormat.MEDIUM);
 
         setTitle("DavMail: Accept certificate ?");
         try {
diff --git a/src/java/davmail/ui/SettingsFrame.java b/src/java/davmail/ui/SettingsFrame.java
index 581fc5bf..150dd08e 100644
--- a/src/java/davmail/ui/SettingsFrame.java
+++ b/src/java/davmail/ui/SettingsFrame.java
@@ -328,7 +328,7 @@ public class SettingsFrame extends JFrame {
 
         tabbedPane.add("Advanced", advancedPanel);
 
-        add("Center", tabbedPane);
+        add(BorderLayout.CENTER, tabbedPane);
 
         JPanel buttonPanel = new JPanel();
         JButton cancel = new JButton("Cancel");
@@ -388,7 +388,7 @@ public class SettingsFrame extends JFrame {
         buttonPanel.add(cancel);
         buttonPanel.add(help);
 
-        add("South", buttonPanel);
+        add(BorderLayout.SOUTH, buttonPanel);
 
         pack();
         //setResizable(false);
diff --git a/src/java/davmail/ui/tray/AwtGatewayTray.java b/src/java/davmail/ui/tray/AwtGatewayTray.java
index 2401da56..c0d910d7 100644
--- a/src/java/davmail/ui/tray/AwtGatewayTray.java
+++ b/src/java/davmail/ui/tray/AwtGatewayTray.java
@@ -18,6 +18,10 @@ import java.awt.event.ActionListener;
  * Tray icon handler based on java 1.6
  */
 public class AwtGatewayTray implements DavGatewayTrayInterface {
+    protected static final String TRAY2_PNG = "tray2.png";
+    protected static final String TRAY_PNG = "tray.png";
+    protected static final String TRAYINACTIVE_PNG = "trayinactive.png";
+
     protected AwtGatewayTray() {
     }
 
@@ -126,9 +130,9 @@ public class AwtGatewayTray implements DavGatewayTrayInterface {
 
         // get the SystemTray instance
         SystemTray tray = SystemTray.getSystemTray();
-        image = DavGatewayTray.loadImage("tray.png");
-        image2 = DavGatewayTray.loadImage("tray2.png");
-        inactiveImage = DavGatewayTray.loadImage("trayinactive.png");
+        image = DavGatewayTray.loadImage(TRAY_PNG);
+        image2 = DavGatewayTray.loadImage(TRAY2_PNG);
+        inactiveImage = DavGatewayTray.loadImage(TRAYINACTIVE_PNG);
 
         // create a popup menu
         PopupMenu popup = new PopupMenu();
diff --git a/src/java/davmail/ui/tray/FrameGatewayTray.java b/src/java/davmail/ui/tray/FrameGatewayTray.java
index e8f59902..30dc71a5 100644
--- a/src/java/davmail/ui/tray/FrameGatewayTray.java
+++ b/src/java/davmail/ui/tray/FrameGatewayTray.java
@@ -192,8 +192,8 @@ public class FrameGatewayTray implements DavGatewayTrayInterface {
         }
 
         image = DavGatewayTray.loadImage("tray.png");
-        image2 = DavGatewayTray.loadImage("tray2.png");
-        inactiveImage = DavGatewayTray.loadImage("trayinactive.png");
+        image2 = DavGatewayTray.loadImage(AwtGatewayTray.TRAY2_PNG);
+        inactiveImage = DavGatewayTray.loadImage(AwtGatewayTray.TRAYINACTIVE_PNG);
 
         mainFrame = new JFrame();
         mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
diff --git a/src/java/davmail/ui/tray/SwtGatewayTray.java b/src/java/davmail/ui/tray/SwtGatewayTray.java
index 60300d2b..658b6875 100644
--- a/src/java/davmail/ui/tray/SwtGatewayTray.java
+++ b/src/java/davmail/ui/tray/SwtGatewayTray.java
@@ -143,8 +143,8 @@ public class SwtGatewayTray implements DavGatewayTrayInterface {
 
                     awtImage = DavGatewayTray.loadImage("tray.png");
                     image = loadSwtImage("tray.png");
-                    image2 = loadSwtImage("tray2.png");
-                    inactiveImage = loadSwtImage("trayinactive.png");
+                    image2 = loadSwtImage(AwtGatewayTray.TRAY2_PNG);
+                    inactiveImage = loadSwtImage(AwtGatewayTray.TRAYINACTIVE_PNG);
 
                     trayItem.setImage(image);