diff --git a/FCL/src/main/java/com/tungsten/fcl/util/ResourceNotFoundError.java b/FCL/src/main/java/com/tungsten/fcl/util/ResourceNotFoundError.java
index 60045053..7a2672e3 100644
--- a/FCL/src/main/java/com/tungsten/fcl/util/ResourceNotFoundError.java
+++ b/FCL/src/main/java/com/tungsten/fcl/util/ResourceNotFoundError.java
@@ -19,7 +19,7 @@ package com.tungsten.fcl.util;
 
 import java.io.InputStream;
 
-public class ResourceNotFoundError extends Error {
+public final class ResourceNotFoundError extends Error {
     public ResourceNotFoundError(String message) {
         super(message);
     }
diff --git a/FCL/src/main/java/com/tungsten/fcl/util/TaskCancellationAction.java b/FCL/src/main/java/com/tungsten/fcl/util/TaskCancellationAction.java
index 262bfd79..b103330f 100644
--- a/FCL/src/main/java/com/tungsten/fcl/util/TaskCancellationAction.java
+++ b/FCL/src/main/java/com/tungsten/fcl/util/TaskCancellationAction.java
@@ -21,7 +21,7 @@ import com.tungsten.fcl.ui.TaskDialog;
 
 import java.util.function.Consumer;
 
-public class TaskCancellationAction {
+public final class TaskCancellationAction {
     public static TaskCancellationAction NORMAL = new TaskCancellationAction(() -> {
     });
 
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/Holder.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/Holder.java
index 8f75551c..6c92340f 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/Holder.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/Holder.java
@@ -17,11 +17,26 @@
  */
 package com.tungsten.fclcore.util;
 
+import com.tungsten.fclcore.fakefx.beans.InvalidationListener;
+import com.tungsten.fclcore.fakefx.beans.Observable;
+
 import java.util.Objects;
 
-public final class Holder<T> {
+public final class Holder<T> implements InvalidationListener {
     public T value;
 
+    public Holder() {
+    }
+
+    public Holder(T value) {
+        this.value = value;
+    }
+
+    @Override
+    public void invalidated(Observable observable) {
+        // no-op
+    }
+
     @Override
     public int hashCode() {
         return Objects.hashCode(value);
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/InvocationDispatcher.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/InvocationDispatcher.java
index 058b08e2..f126ebbc 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/InvocationDispatcher.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/InvocationDispatcher.java
@@ -17,13 +17,12 @@
  */
 package com.tungsten.fclcore.util;
 
-import java.util.Optional;
 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
-public class InvocationDispatcher<ARG> implements Consumer<ARG> {
+public final class InvocationDispatcher<ARG> implements Consumer<ARG> {
 
     public static <ARG> InvocationDispatcher<ARG> runOn(Executor executor, Consumer<ARG> action) {
         return new InvocationDispatcher<>(arg -> executor.execute(() -> {
@@ -33,9 +32,8 @@ public class InvocationDispatcher<ARG> implements Consumer<ARG> {
         }));
     }
 
-    private Consumer<Supplier<ARG>> handler;
-
-    private AtomicReference<Optional<ARG>> pendingArg = new AtomicReference<>();
+    private final Consumer<Supplier<ARG>> handler;
+    private final AtomicReference<Holder<ARG>> pendingArg = new AtomicReference<>();
 
     public InvocationDispatcher(Consumer<Supplier<ARG>> handler) {
         this.handler = handler;
@@ -43,8 +41,8 @@ public class InvocationDispatcher<ARG> implements Consumer<ARG> {
 
     @Override
     public void accept(ARG arg) {
-        if (pendingArg.getAndSet(Optional.ofNullable(arg)) == null) {
-            handler.accept(() -> pendingArg.getAndSet(null).orElse(null));
+        if (pendingArg.getAndSet(new Holder<>(arg)) == null) {
+            handler.accept(() -> pendingArg.getAndSet(null).value);
         }
     }
 }
\ No newline at end of file
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/StringUtils.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/StringUtils.java
index 2cb0df5b..a6d96554 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/StringUtils.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/StringUtils.java
@@ -404,7 +404,7 @@ public final class StringUtils {
     /**
      * Class for computing the longest common subsequence between strings.
      */
-    public static class LongestCommonSubsequence {
+    public static final class LongestCommonSubsequence {
         // We reuse dynamic programming storage array here to reduce allocations.
         private final int[][] f;
         private final int maxLengthA;
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/ToStringBuilder.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/ToStringBuilder.java
index f8ebbb67..74143987 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/ToStringBuilder.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/ToStringBuilder.java
@@ -17,7 +17,7 @@
  */
 package com.tungsten.fclcore.util;
 
-public class ToStringBuilder {
+public final class ToStringBuilder {
 
     private final StringBuilder stringBuilder;
     private boolean first = true;
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/EnumOrdinalDeserializer.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/EnumOrdinalDeserializer.java
index d6aa5a61..ed64e92d 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/EnumOrdinalDeserializer.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/EnumOrdinalDeserializer.java
@@ -27,9 +27,9 @@ import java.lang.reflect.Type;
 import java.util.HashMap;
 import java.util.Map;
 
-public class EnumOrdinalDeserializer<T extends Enum<T>> implements JsonDeserializer<T> {
+public final class EnumOrdinalDeserializer<T extends Enum<T>> implements JsonDeserializer<T> {
 
-    private Map<String, T> mapping = new HashMap<>();
+    private final Map<String, T> mapping = new HashMap<>();
 
     public EnumOrdinalDeserializer(Class<T> enumClass) {
         for (T constant : enumClass.getEnumConstants()) {
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/JsonMap.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/JsonMap.java
index a0d5c9ea..e7e24255 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/JsonMap.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/JsonMap.java
@@ -26,7 +26,7 @@ import java.util.Map;
  * @param <K>
  * @param <V>
  */
-public class JsonMap<K, V> extends HashMap<K, V> {
+public final class JsonMap<K, V> extends HashMap<K, V> {
     public JsonMap(int initialCapacity, float loadFactor) {
         super(initialCapacity, loadFactor);
     }
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/JsonTypeAdapterFactory.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/JsonTypeAdapterFactory.java
index d36796f8..b577dc7f 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/JsonTypeAdapterFactory.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/gson/JsonTypeAdapterFactory.java
@@ -27,7 +27,7 @@ import java.io.IOException;
 import java.util.HashMap;
 import java.util.Map;
 
-public class JsonTypeAdapterFactory implements TypeAdapterFactory {
+public final class JsonTypeAdapterFactory implements TypeAdapterFactory {
 
     public static final JsonTypeAdapterFactory INSTANCE = new JsonTypeAdapterFactory();
 
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/io/ChecksumMismatchException.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/io/ChecksumMismatchException.java
index 7f911465..b020b613 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/io/ChecksumMismatchException.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/io/ChecksumMismatchException.java
@@ -23,7 +23,7 @@ import com.tungsten.fclcore.util.DigestUtils;
 import java.io.IOException;
 import java.nio.file.Path;
 
-public class ChecksumMismatchException extends ArtifactMalformedException {
+public final class ChecksumMismatchException extends ArtifactMalformedException {
 
     private final String algorithm;
     private final String expectedChecksum;
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/io/HttpMultipartRequest.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/io/HttpMultipartRequest.java
index 7097b482..3c8e62a9 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/io/HttpMultipartRequest.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/io/HttpMultipartRequest.java
@@ -26,8 +26,8 @@ import java.net.HttpURLConnection;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
 
-public class HttpMultipartRequest implements Closeable {
-    private static final String endl = "\r\n";
+public final class HttpMultipartRequest implements Closeable {
+    private static final byte[] ENDL = {'\r', '\n'};
 
     private final String boundary = "*****" + System.currentTimeMillis() + "*****";
     private final HttpURLConnection urlConnection;
@@ -44,7 +44,7 @@ public class HttpMultipartRequest implements Closeable {
 
     private void addLine(String content) throws IOException {
         stream.write(content.getBytes(UTF_8));
-        stream.write(endl.getBytes(UTF_8));
+        stream.write(ENDL);
     }
 
     public HttpMultipartRequest file(String name, String filename, String contentType, InputStream inputStream) throws IOException {
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/io/ResponseCodeException.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/io/ResponseCodeException.java
index 20dc982e..14690b8c 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/io/ResponseCodeException.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/io/ResponseCodeException.java
@@ -20,7 +20,7 @@ package com.tungsten.fclcore.util.io;
 import java.io.IOException;
 import java.net.URL;
 
-public class ResponseCodeException extends IOException {
+public final class ResponseCodeException extends IOException {
 
     private final URL url;
     private final int responseCode;
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/io/Unzipper.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/io/Unzipper.java
index b61faf36..c195519e 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/io/Unzipper.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/io/Unzipper.java
@@ -24,7 +24,7 @@ import java.nio.charset.StandardCharsets;
 import java.nio.file.*;
 import java.nio.file.attribute.BasicFileAttributes;
 
-public class Unzipper {
+public final class Unzipper {
     private final Path zipFile, dest;
     private boolean replaceExistentFile = false;
     private boolean terminateIfSubDirectoryNotExists = false;
diff --git a/FCLCore/src/main/java/com/tungsten/fclcore/util/skin/NormalizedSkin.java b/FCLCore/src/main/java/com/tungsten/fclcore/util/skin/NormalizedSkin.java
index df681a7c..0c5a3097 100644
--- a/FCLCore/src/main/java/com/tungsten/fclcore/util/skin/NormalizedSkin.java
+++ b/FCLCore/src/main/java/com/tungsten/fclcore/util/skin/NormalizedSkin.java
@@ -23,7 +23,7 @@ import android.graphics.Bitmap;
  * Describes a Minecraft 1.8+ skin (64x64).
  * Old format skins are converted to the new format.
  */
-public class NormalizedSkin {
+public final class NormalizedSkin {
 
     private static void copyImage(Bitmap src, Bitmap dst, int sx, int sy, int dx, int dy, int w, int h, boolean flipHorizontal) {
         for (int y = 0; y < h; y++) {