content: // 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 static com.google.protobuf.Internal.checkNotNull;
  
  import com.google.protobuf.Internal.EnumLite;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * Internal representation of map fields in generated lite-runtime messages.
   *
   * <p>This class is a protobuf implementation detail. Users shouldn't use this class directly.
   */
  public final class MapFieldLite<K, V> extends LinkedHashMap<K, V> {
  
    private boolean isMutable;
  
    private MapFieldLite() {
      this.isMutable = true;
    }
  
    private MapFieldLite(Map<K, V> mapData) {
      super(mapData);
      this.isMutable = true;
    }
  
    @SuppressWarnings({"rawtypes", "unchecked"})
    private static final MapFieldLite EMPTY_MAP_FIELD = new MapFieldLite();
  
    static {
      EMPTY_MAP_FIELD.makeImmutable();
    }
  
    /** 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;
    }
  
    public void mergeFrom(MapFieldLite<K, V> other) {
      ensureMutable();
      if (!other.isEmpty()) {
        putAll(other);
      }
    }
  
    @SuppressWarnings({"unchecked", "cast"})
    @Override
    public Set<Map.Entry<K, V>> entrySet() {
      return isEmpty() ? Collections.<Map.Entry<K, V>>emptySet() : super.entrySet();
    }
  
    @Override
    public void clear() {
      ensureMutable();
      super.clear();
    }
  
    @Override
    public V put(K key, V value) {
      ensureMutable();
      checkNotNull(key);
  
      checkNotNull(value);
      return super.put(key, value);
    }
  
    public V put(Map.Entry<K, V> entry) {
      return put(entry.getKey(), entry.getValue());
    }
  
    @Override
    public void putAll(Map<? extends K, ? extends V> m) {
      ensureMutable();
      checkForNullKeysAndValues(m);
      super.putAll(m);
    }
  
    @Override
    public V remove(Object key) {
      ensureMutable();
      return super.remove(key);
    }
  
    private static void checkForNullKeysAndValues(Map<?, ?> m) {
      for (Object key : m.keySet()) {
        checkNotNull(key);
        checkNotNull(m.get(key));
      }
    }
  
    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() != b.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) {
      return (object instanceof Map) && equals(this, (Map<K, V>) object);
    }
  
    private static int calculateHashCodeForObject(Object a) {
      if (a instanceof byte[]) {
        return Internal.hashCode((byte[]) a);
      }
      // Enums should be stored as integers internally.
      if (a instanceof EnumLite) {
        throw new UnsupportedOperationException();
      }
      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(this);
    }
  
    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 LinkedHashMap<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> mutableCopy() {
      return isEmpty() ? new MapFieldLite<K, V>() : new MapFieldLite<K, V>(this);
    }
  
    /**
     * Makes this field immutable. All subsequent modifications will throw an {@link
     * UnsupportedOperationException}.
     */
    public void makeImmutable() {
      isMutable = false;
    }
  
    /** Returns whether this field can be modified. */
    public boolean isMutable() {
      return isMutable;
    }
  
    private void ensureMutable() {
      if (!isMutable()) {
        throw new UnsupportedOperationException();
      }
    }
  }
  