diff --git a/src/com/annimon/turrets/Background.java b/src/com/annimon/turrets/Background.java
index 74df343..03642dd 100644
--- a/src/com/annimon/turrets/Background.java
+++ b/src/com/annimon/turrets/Background.java
@@ -10,7 +10,7 @@ import java.awt.Graphics;
  *
  * @author aNNiMON
  */
-public class Background {
+public final class Background {
     
     private static final int STARS_COUNT = (int) Math.sqrt(WIDTH * HEIGHT);
     
diff --git a/src/com/annimon/turrets/GameCanvas.java b/src/com/annimon/turrets/GameCanvas.java
index ffe8f79..40b8abb 100644
--- a/src/com/annimon/turrets/GameCanvas.java
+++ b/src/com/annimon/turrets/GameCanvas.java
@@ -21,7 +21,7 @@ import java.io.IOException;
  *
  * @author aNNiMON
  */
-public class GameCanvas extends DoubleBufferedCanvas implements Runnable, NetworkListener {
+public final class GameCanvas extends DoubleBufferedCanvas implements Runnable, NetworkListener {
     
     private static final String WAIT_MESSAGE = "Please, wait...";
     private static final int WIN = 1, LOOSE = -1, NOTHING = 0;
diff --git a/src/com/annimon/turrets/Main.java b/src/com/annimon/turrets/Main.java
index 4a8e1cd..0a20d19 100644
--- a/src/com/annimon/turrets/Main.java
+++ b/src/com/annimon/turrets/Main.java
@@ -5,13 +5,12 @@ import com.annimon.turrets.util.GuiUtil;
 import com.annimon.turrets.util.Prefs;
 import java.awt.Component;
 import javax.swing.JFrame;
-import javax.swing.JLayer;
 
 /**
  *
  * @author aNNiMON
  */
-public class Main extends JFrame {
+public final class Main extends JFrame {
     
     private static Main instance;
 
diff --git a/src/com/annimon/turrets/MenuPanel.java b/src/com/annimon/turrets/MenuPanel.java
index 4a582cd..791395e 100644
--- a/src/com/annimon/turrets/MenuPanel.java
+++ b/src/com/annimon/turrets/MenuPanel.java
@@ -22,7 +22,7 @@ import javax.swing.event.ListSelectionListener;
  * Main menu
  * @author aNNiMON
  */
-public class MenuPanel extends JPanel {
+public final class MenuPanel extends JPanel {
     
     private static final String[] MENU_ITEMS = {
         "Create Game", "Join", "Options", "Help", "Exit"
diff --git a/src/com/annimon/turrets/OptionsPanel.java b/src/com/annimon/turrets/OptionsPanel.java
index f95a642..dd15af6 100644
--- a/src/com/annimon/turrets/OptionsPanel.java
+++ b/src/com/annimon/turrets/OptionsPanel.java
@@ -25,7 +25,7 @@ import javax.swing.text.MaskFormatter;
  *
  * @author aNNiMON
  */
-public class OptionsPanel extends JPanel {
+public final class OptionsPanel extends JPanel {
     
     private static final Font FONT = new Font("Stencil", 1, 30);
     private static final int VERT_INSET = 80, HOR_INSET = 50;
diff --git a/src/com/annimon/turrets/ShootInfo.java b/src/com/annimon/turrets/ShootInfo.java
index 00adb73..b55721d 100644
--- a/src/com/annimon/turrets/ShootInfo.java
+++ b/src/com/annimon/turrets/ShootInfo.java
@@ -11,7 +11,7 @@ import java.awt.Graphics2D;
  *
  * @author aNNiMON
  */
-public class ShootInfo {
+public final class ShootInfo {
     
     double x, y, speedX;
     double windSpeed, vsin, t;
diff --git a/src/com/annimon/turrets/Terrain.java b/src/com/annimon/turrets/Terrain.java
index fb7e660..fb82ec5 100644
--- a/src/com/annimon/turrets/Terrain.java
+++ b/src/com/annimon/turrets/Terrain.java
@@ -12,7 +12,7 @@ import java.awt.LinearGradientPaint;
  * Destructible terrain.
  * @author aNNiMON
  */
-public class Terrain {
+public final class Terrain {
 
     private static final Color[] TERRAIN_COLOR = {
         new Color(0xFF33CE2B), new Color(0xFF1C7317)
diff --git a/src/com/annimon/turrets/Turret.java b/src/com/annimon/turrets/Turret.java
index d89d997..6b661fa 100644
--- a/src/com/annimon/turrets/Turret.java
+++ b/src/com/annimon/turrets/Turret.java
@@ -12,7 +12,7 @@ import java.awt.Graphics2D;
  *
  * @author aNNiMON
  */
-public class Turret {
+public final class Turret {
     
     public static final boolean SERVER = true, CLIENT = false;
     
diff --git a/src/com/annimon/turrets/Wind.java b/src/com/annimon/turrets/Wind.java
index a39adb2..ec11b92 100644
--- a/src/com/annimon/turrets/Wind.java
+++ b/src/com/annimon/turrets/Wind.java
@@ -11,7 +11,7 @@ import java.awt.Graphics2D;
  *
  * @author aNNiMON
  */
-public class Wind {
+public final class Wind {
     
     private double speed;
 
diff --git a/src/com/annimon/turrets/network/GameClient.java b/src/com/annimon/turrets/network/GameClient.java
index 728f9c9..aef7473 100644
--- a/src/com/annimon/turrets/network/GameClient.java
+++ b/src/com/annimon/turrets/network/GameClient.java
@@ -8,7 +8,7 @@ import java.net.Socket;
  *
  * @author aNNiMON
  */
-public class GameClient {
+public final class GameClient {
 
     private final SocketHelper helper;
 
diff --git a/src/com/annimon/turrets/network/GameServer.java b/src/com/annimon/turrets/network/GameServer.java
index 3eac146..7792f3d 100644
--- a/src/com/annimon/turrets/network/GameServer.java
+++ b/src/com/annimon/turrets/network/GameServer.java
@@ -10,7 +10,7 @@ import java.net.UnknownHostException;
  *
  * @author aNNiMON
  */
-public class GameServer {
+public final class GameServer {
 
     private final ServerSocket serverSocket;
     private final SocketHelper helper;
diff --git a/src/com/annimon/turrets/network/SocketHelper.java b/src/com/annimon/turrets/network/SocketHelper.java
index 6b8a464..89cb84f 100644
--- a/src/com/annimon/turrets/network/SocketHelper.java
+++ b/src/com/annimon/turrets/network/SocketHelper.java
@@ -11,7 +11,7 @@ import java.net.Socket;
  *
  * @author aNNiMON
  */
-public class SocketHelper extends Thread {
+public final class SocketHelper extends Thread {
 
     private final Socket socket;
     private final DataInputStream dis;
diff --git a/src/com/annimon/turrets/util/ExceptionHandler.java b/src/com/annimon/turrets/util/ExceptionHandler.java
index 2515bae..c90af4b 100644
--- a/src/com/annimon/turrets/util/ExceptionHandler.java
+++ b/src/com/annimon/turrets/util/ExceptionHandler.java
@@ -1,25 +1,25 @@
-package com.annimon.turrets.util;
-
-import com.annimon.turrets.Constants;
-
-/**
- * Handle exceptions.
- * @author aNNiMON
- */
-public class ExceptionHandler {
-    
-    private static final boolean DEBUG_MODE = Constants.DEBUG_MODE;
-    
-    public static void handle(Throwable throwable) {
-        if (DEBUG_MODE) {
-            throwable.printStackTrace();
-        }
-    }
-    
-    public static void handle(Throwable throwable, String comment) {
-        if (DEBUG_MODE) {
-            System.out.println(comment);
-            handle(throwable);
-        }
-    }
-}
+package com.annimon.turrets.util;
+
+import com.annimon.turrets.Constants;
+
+/**
+ * Handle exceptions.
+ * @author aNNiMON
+ */
+public final class ExceptionHandler {
+    
+    private static final boolean DEBUG_MODE = Constants.DEBUG_MODE;
+    
+    public static void handle(Throwable throwable) {
+        if (DEBUG_MODE) {
+            throwable.printStackTrace();
+        }
+    }
+    
+    public static void handle(Throwable throwable, String comment) {
+        if (DEBUG_MODE) {
+            System.out.println(comment);
+            handle(throwable);
+        }
+    }
+}
diff --git a/src/com/annimon/turrets/util/GuiUtil.java b/src/com/annimon/turrets/util/GuiUtil.java
index 9929569..c5c5efe 100644
--- a/src/com/annimon/turrets/util/GuiUtil.java
+++ b/src/com/annimon/turrets/util/GuiUtil.java
@@ -17,7 +17,7 @@ import javax.swing.plaf.LayerUI;
  *
  * @author aNNiMON
  */
-public class GuiUtil {
+public final class GuiUtil {
     
     public static <T extends JComponent> JLayer<T> createPlanetLayer(T component) {
         return new JLayer<>(component, (LayerUI<T>) new PlanetBackground());
diff --git a/src/com/annimon/turrets/util/RandomExt.java b/src/com/annimon/turrets/util/RandomExt.java
index b28a5f0..ca248ae 100644
--- a/src/com/annimon/turrets/util/RandomExt.java
+++ b/src/com/annimon/turrets/util/RandomExt.java
@@ -6,7 +6,7 @@ import java.util.Random;
  * Extended random
  * @author aNNiMON
  */
-public class RandomExt extends Random {
+public final class RandomExt extends Random {
     
     public RandomExt() {
         super();
diff --git a/src/com/annimon/turrets/util/Util.java b/src/com/annimon/turrets/util/Util.java
index 662a7a2..ccd8b76 100644
--- a/src/com/annimon/turrets/util/Util.java
+++ b/src/com/annimon/turrets/util/Util.java
@@ -4,7 +4,7 @@ package com.annimon.turrets.util;
  *
  * @author aNNiMON
  */
-public class Util {
+public final class Util {
     
     private static final RandomExt random = new RandomExt();