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diff --git a/java/src/main/java/com/google/protobuf/MapFieldLite.java b/java/src/main/java/com/google/protobuf/MapFieldLite.java
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+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Internal representation of map fields in generated lite-runtime messages.
+ * 
+ * This class is a protobuf implementation detail. Users shouldn't use this
+ * class directly.
+ */
+public class MapFieldLite<K, V> {
+  private Map<K, V> mapData;
+  
+  private MapFieldLite(Map<K, V> mapData) {
+    this.mapData = mapData;
+  }
+  
+  @SuppressWarnings({"rawtypes", "unchecked"})
+  private static final MapFieldLite EMPTY_MAP_FIELD =
+      new MapFieldLite(Collections.emptyMap());
+  
+  /** Returns an singleton immutable empty MapFieldLite instance. */
+  @SuppressWarnings({"unchecked", "cast"})
+  public static <K, V> MapFieldLite<K, V> emptyMapField() {
+    return (MapFieldLite<K, V>) EMPTY_MAP_FIELD;
+  }
+  
+  /** Creates a new MapFieldLite instance. */
+  public static <K, V> MapFieldLite<K, V> newMapField() {
+    return new MapFieldLite<K, V>(new HashMap<K, V>());
+  }
+  
+  /** Gets the content of this MapField as a read-only Map. */
+  public Map<K, V> getMap() {
+    return Collections.unmodifiableMap(mapData);
+  }
+  
+  /** Gets a mutable Map view of this MapField. */
+  public Map<K, V> getMutableMap() {
+    return mapData;
+  }
+  
+  public void mergeFrom(MapFieldLite<K, V> other) {
+    mapData.putAll(copy(other.mapData));
+  }
+  
+  public void clear() {
+    mapData.clear();
+  }
+  
+  private static boolean equals(Object a, Object b) {
+    if (a instanceof byte[] && b instanceof byte[]) {
+      return Arrays.equals((byte[]) a, (byte[]) b);
+    }
+    return a.equals(b);
+  }
+  
+  /**
+   * Checks whether two {@link Map}s are equal. We don't use the default equals
+   * method of {@link Map} because it compares by identity not by content for
+   * byte arrays.
+   */
+  static <K, V> boolean equals(Map<K, V> a, Map<K, V> b) {
+    if (a == b) {
+      return true;
+    }
+    if (a.size() != a.size()) {
+      return false;
+    }
+    for (Map.Entry<K, V> entry : a.entrySet()) {
+      if (!b.containsKey(entry.getKey())) {
+        return false;
+      }
+      if (!equals(entry.getValue(), b.get(entry.getKey()))) {
+        return false;
+      }
+    }
+    return true;
+  }
+  
+  /**
+   * Checks whether two map fields are equal.
+   */
+  @SuppressWarnings("unchecked")
+  @Override
+  public boolean equals(Object object) {
+    if (!(object instanceof MapFieldLite)) {
+      return false;
+    }
+    MapFieldLite<K, V> other = (MapFieldLite<K, V>) object;
+    return equals(mapData, other.mapData);
+  }
+  
+  private static int calculateHashCodeForObject(Object a) {
+    if (a instanceof byte[]) {
+      return LiteralByteString.hashCode((byte[]) a);
+    }
+    if (a instanceof Internal.EnumLite) {
+      return Internal.hashEnum((Internal.EnumLite) a);
+    }
+    return a.hashCode();
+  }
+
+  /**
+   * Calculates the hash code for a {@link Map}. We don't use the default hash
+   * code method of {@link Map} because for byte arrays and protobuf enums it
+   * use {@link Object#hashCode()}.
+   */
+  static <K, V> int calculateHashCodeForMap(Map<K, V> a) {
+    int result = 0;
+    for (Map.Entry<K, V> entry : a.entrySet()) {
+      result += calculateHashCodeForObject(entry.getKey())
+          ^ calculateHashCodeForObject(entry.getValue());
+    }
+    return result;    
+  }
+  
+  @Override
+  public int hashCode() {
+    return calculateHashCodeForMap(mapData);
+  }
+  
+  private static Object copy(Object object) {
+    if (object instanceof byte[]) {
+      byte[] data = (byte[]) object;
+      return Arrays.copyOf(data, data.length);
+    }
+    return object;
+  }
+  
+  /**
+   * Makes a deep copy of a {@link Map}. Immutable objects in the map will be
+   * shared (e.g., integers, strings, immutable messages) and mutable ones will
+   * have a copy (e.g., byte arrays, mutable messages).
+   */
+  @SuppressWarnings("unchecked")
+  static <K, V> Map<K, V> copy(Map<K, V> map) {
+    Map<K, V> result = new HashMap<K, V>();
+    for (Map.Entry<K, V> entry : map.entrySet()) {
+      result.put(entry.getKey(), (V) copy(entry.getValue()));
+    }
+    return result;
+  }
+  
+  /** Returns a deep copy of this map field. */
+  public MapFieldLite<K, V> copy() {
+    return new MapFieldLite<K, V>(copy(mapData));
+  }
+}