diff --git a/shell/platform/android/io/flutter/plugin/common/FlutterMessageChannel.java b/shell/platform/android/io/flutter/plugin/common/FlutterMessageChannel.java
index 001ab35cf61..b8d8f53fb3d 100644
--- a/shell/platform/android/io/flutter/plugin/common/FlutterMessageChannel.java
+++ b/shell/platform/android/io/flutter/plugin/common/FlutterMessageChannel.java
@@ -10,8 +10,6 @@ import io.flutter.view.FlutterView.BinaryMessageReplyCallback;
 import io.flutter.view.FlutterView.BinaryMessageResponse;
 import io.flutter.view.FlutterView.OnBinaryMessageListenerAsync;
 import java.nio.ByteBuffer;
-import java.util.Objects;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
  * A named channel for communicating with the Flutter application using semi-structured messages.
@@ -43,9 +41,12 @@ public final class FlutterMessageChannel<T> {
      * @param codec a {@link MessageCodec}.
      */
     public FlutterMessageChannel(FlutterView view, String name, MessageCodec<T> codec) {
-        this.view = Objects.requireNonNull(view);
-        this.name = Objects.requireNonNull(name);
-        this.codec = Objects.requireNonNull(codec);
+        assert view != null;
+        assert name != null;
+        assert codec != null;
+        this.view = view;
+        this.name = name;
+        this.codec = codec;
     }
 
     /**
diff --git a/shell/platform/android/io/flutter/plugin/common/FlutterMethodChannel.java b/shell/platform/android/io/flutter/plugin/common/FlutterMethodChannel.java
index 1a980233c44..5cadc0f2ef6 100644
--- a/shell/platform/android/io/flutter/plugin/common/FlutterMethodChannel.java
+++ b/shell/platform/android/io/flutter/plugin/common/FlutterMethodChannel.java
@@ -9,7 +9,6 @@ import io.flutter.view.FlutterView;
 import io.flutter.view.FlutterView.BinaryMessageResponse;
 import io.flutter.view.FlutterView.OnBinaryMessageListenerAsync;
 import java.nio.ByteBuffer;
-import java.util.Objects;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
@@ -53,9 +52,12 @@ public final class FlutterMethodChannel {
      * @param codec a {@link MessageCodec}.
      */
     public FlutterMethodChannel(FlutterView view, String name, MethodCodec codec) {
-        this.view = Objects.requireNonNull(view);
-        this.name = Objects.requireNonNull(name);
-        this.codec = Objects.requireNonNull(codec);
+        assert view != null;
+        assert name != null;
+        assert codec != null;
+        this.view = view;
+        this.name = name;
+        this.codec = codec;
     }
 
     /**
diff --git a/shell/platform/android/io/flutter/plugin/common/MethodCall.java b/shell/platform/android/io/flutter/plugin/common/MethodCall.java
index 81843832988..3643bb5e455 100644
--- a/shell/platform/android/io/flutter/plugin/common/MethodCall.java
+++ b/shell/platform/android/io/flutter/plugin/common/MethodCall.java
@@ -27,7 +27,8 @@ public final class MethodCall {
      * @param arguments the arguments, a value supported by the channel's message codec.
      */
     public MethodCall(String method, Object arguments) {
-        this.method = Objects.requireNonNull(method);
+        assert method != null;
+        this.method = method;
         this.arguments = arguments;
     }
 }
diff --git a/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java b/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java
index 99079ba84da..038dd90b4df 100644
--- a/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java
+++ b/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java
@@ -7,7 +7,7 @@ package io.flutter.plugin.common;
 import java.io.ByteArrayOutputStream;
 import java.math.BigInteger;
 import java.nio.ByteBuffer;
-import java.nio.charset.StandardCharsets;
+import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
@@ -65,6 +65,7 @@ public final class StandardMessageCodec implements MessageCodec<Object> {
         return value;
     }
 
+    private static final Charset UTF8 = Charset.forName("UTF8");
     private static final byte NULL = 0;
     private static final byte TRUE = 1;
     private static final byte FALSE = 2;
@@ -84,7 +85,7 @@ public final class StandardMessageCodec implements MessageCodec<Object> {
         assert 0 <= value;
         if (value < 254) {
             stream.write(value);
-        } else if (value < 0xffff) {
+        } else if (value <= 0xffff) {
             stream.write(254);
             stream.write(value >>> 8);
             stream.write(value);
@@ -150,13 +151,13 @@ public final class StandardMessageCodec implements MessageCodec<Object> {
             } else if (value instanceof BigInteger) {
                 stream.write(BIGINT);
                 writeBytes(stream,
-                    ((BigInteger) value).toString(16).getBytes(StandardCharsets.UTF_8));
+                    ((BigInteger) value).toString(16).getBytes(UTF8));
             } else {
                 throw new IllegalArgumentException("Unsupported Number type: " + value.getClass());
             }
         } else if (value instanceof String) {
             stream.write(STRING);
-            writeBytes(stream, ((String) value).getBytes(StandardCharsets.UTF_8));
+            writeBytes(stream, ((String) value).getBytes(UTF8));
         } else if (value instanceof byte[]) {
             stream.write(BYTE_ARRAY);
             writeBytes(stream, (byte[]) value);
@@ -259,7 +260,7 @@ public final class StandardMessageCodec implements MessageCodec<Object> {
                 break;
             case BIGINT: {
                 final byte[] hex = readBytes(buffer);
-                result = new BigInteger(new String(hex, StandardCharsets.UTF_8), 16);
+                result = new BigInteger(new String(hex, UTF8), 16);
                 break;
             }
             case DOUBLE:
@@ -267,7 +268,7 @@ public final class StandardMessageCodec implements MessageCodec<Object> {
                 break;
             case STRING: {
                 final byte[] bytes = readBytes(buffer);
-                result = new String(bytes, StandardCharsets.UTF_8);
+                result = new String(bytes, UTF8);
                 break;
             }
             case BYTE_ARRAY: {
diff --git a/shell/platform/android/io/flutter/plugin/common/StringMessageCodec.java b/shell/platform/android/io/flutter/plugin/common/StringMessageCodec.java
index f47e39c2a22..0ae415c8a3b 100644
--- a/shell/platform/android/io/flutter/plugin/common/StringMessageCodec.java
+++ b/shell/platform/android/io/flutter/plugin/common/StringMessageCodec.java
@@ -5,13 +5,14 @@
 package io.flutter.plugin.common;
 
 import java.nio.ByteBuffer;
-import java.nio.charset.StandardCharsets;
+import java.nio.charset.Charset;
 
 /**
  * A {@link MessageCodec} using UTF-8 encoded String messages.
  */
 public final class StringMessageCodec implements MessageCodec<String> {
     // This codec must match the Dart codec of the same name in package flutter/services.
+    private static final Charset UTF8 = Charset.forName("UTF8");
     public static final StringMessageCodec INSTANCE = new StringMessageCodec();
 
     private StringMessageCodec() {
@@ -23,7 +24,7 @@ public final class StringMessageCodec implements MessageCodec<String> {
             return null;
         }
         // TODO(mravn): Avoid the extra copy below.
-        final byte[] bytes = message.getBytes(StandardCharsets.UTF_8);
+        final byte[] bytes = message.getBytes(UTF8);
         final ByteBuffer buffer = ByteBuffer.allocateDirect(bytes.length);
         buffer.put(bytes);
         return buffer;
@@ -46,6 +47,6 @@ public final class StringMessageCodec implements MessageCodec<String> {
             message.get(bytes);
             offset = 0;
         }
-        return new String(bytes, offset, length, StandardCharsets.UTF_8);
+        return new String(bytes, offset, length, UTF8);
     }
 }