/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.collections4.map;
  
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.io.Serializable;
  import java.util.Map;
  import java.util.Objects;
  
  import org.apache.commons.collections4.MapIterator;
  import org.apache.commons.collections4.keyvalue.MultiKey;
  
  /**
   * A {@code Map} implementation that uses multiple keys to map the value.
   * <p>
   * This class is the most efficient way to uses multiple keys to map to a value.
   * The best way to use this class is via the additional map-style methods.
   * These provide {@code get}, {@code containsKey}, {@code put} and
   * {@code remove} for individual keys which operate without extra object creation.
   * </p>
   * <p>
   * The additional methods are the main interface of this map.
   * As such, you will not normally hold this map in a variable of type {@code Map}.
   * </p>
   * <p>
   * The normal map methods take in and return a {@link MultiKey}.
   * If you try to use {@code put()} with any other object type a
   * {@code ClassCastException} is thrown. If you try to use {@code null} as
   * the key in {@code put()} a {@code NullPointerException} is thrown.
   * </p>
   * <p>
   * This map is implemented as a decorator of a {@code AbstractHashedMap} which
   * enables extra behavior to be added easily.
   * </p>
   * <ul>
   * <li>{@code MultiKeyMap.decorate(new LinkedMap())} creates an ordered map.
   * <li>{@code MultiKeyMap.decorate(new LRUMap())} creates an least recently used map.
   * <li>{@code MultiKeyMap.decorate(new ReferenceMap())} creates a garbage collector sensitive map.
   * </ul>
   * <p>
   * Note that {@code IdentityMap} and {@code ReferenceIdentityMap} are unsuitable
   * for use as the key comparison would work on the whole MultiKey, not the elements within.
   * </p>
   * <p>
   * As an example, consider a least recently used cache that uses a String airline code
   * and a Locale to lookup the airline's name:
   * </p>
   * <pre>
   * private MultiKeyMap cache = MultiKeyMap.multiKeyMap(new LRUMap(50));
   *
   * public String getAirlineName(String code, String locale) {
   *   String name = (String) cache.get(code, locale);
   *   if (name == null) {
   *     name = getAirlineNameFromDB(code, locale);
   *     cache.put(code, locale, name);
   *   }
   *   return name;
   * }
   * </pre>
   * <p>
   * <strong>Note that MultiKeyMap is not synchronized and is not thread-safe.</strong>
   * If you wish to use this map from multiple threads concurrently, you must use
   * appropriate synchronization. This class may throw exceptions when accessed
   * by concurrent threads without synchronization.
   * </p>
   *
   * @param <K> the type of the keys in this map
   * @param <V> the type of the values in this map
   * @since 3.1
   */
  public class MultiKeyMap<K, V> extends AbstractMapDecorator<MultiKey<? extends K>, V>
          implements Serializable, Cloneable {
  
      /** Serialisation version */
      private static final long serialVersionUID = -1788199231038721040L;
  
      /**
       * Decorates the specified map to add the MultiKeyMap API and fast query.
       * The map must not be null and must be empty.
       *
       * @param <K>  the key type
       * @param <V>  the value type
       * @param map  the map to decorate, not null
      * @return a new multi key map
      * @throws NullPointerException if map is null
      * @throws IllegalArgumentException if the map is not empty
      * @since 4.0
      */
     public static <K, V> MultiKeyMap<K, V> multiKeyMap(final AbstractHashedMap<MultiKey<? extends K>, V> map) {
         Objects.requireNonNull(map, "map");
         if (map.isEmpty()) {
             return new MultiKeyMap<>(map);
         }
         throw new IllegalArgumentException("Map must be empty");
     }
 
     /**
      * Constructs a new MultiKeyMap that decorates a {@code HashedMap}.
      */
     public MultiKeyMap() {
         this(new HashedMap<>());
     }
 
     /**
      * Constructor that decorates the specified map and is called from
      * {@link #multiKeyMap(AbstractHashedMap)}.
      * The map must not be null and should be empty or only contain valid keys.
      * This constructor performs no validation.
      *
      * @param map  the map to decorate
      */
     protected MultiKeyMap(final AbstractHashedMap<MultiKey<? extends K>, V> map) {
         super(map);
         this.map = map;
     }
 
     /**
      * Check to ensure that input keys are valid MultiKey objects.
      *
      * @param key  the key to check
      */
     protected void checkKey(final MultiKey<?> key) {
         Objects.requireNonNull(key, "key");
     }
 
     /**
      * Clones the map without cloning the keys or values.
      *
      * @return a shallow clone
      */
     @SuppressWarnings("unchecked")
     @Override
     public MultiKeyMap<K, V> clone() {
         try {
             return (MultiKeyMap<K, V>) super.clone();
         } catch (final CloneNotSupportedException e) {
             throw new UnsupportedOperationException(e);
         }
     }
 
     /**
      * Checks whether the map contains the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @return true if the map contains the key
      */
     public boolean containsKey(final Object key1, final Object key2) {
         final int hashCode = hash(key1, key2);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry =
                 decorated().data[decorated().hashIndex(hashCode, decorated().data.length)];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2)) {
                 return true;
             }
             entry = entry.next;
         }
         return false;
     }
 
     /**
      * Checks whether the map contains the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @return true if the map contains the key
      */
     public boolean containsKey(final Object key1, final Object key2, final Object key3) {
         final int hashCode = hash(key1, key2, key3);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry =
                 decorated().data[decorated().hashIndex(hashCode, decorated().data.length)];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3)) {
                 return true;
             }
             entry = entry.next;
         }
         return false;
     }
 
     /**
      * Checks whether the map contains the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @return true if the map contains the key
      */
     public boolean containsKey(final Object key1, final Object key2, final Object key3, final Object key4) {
         final int hashCode = hash(key1, key2, key3, key4);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry =
                 decorated().data[decorated().hashIndex(hashCode, decorated().data.length)];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3, key4)) {
                 return true;
             }
             entry = entry.next;
         }
         return false;
     }
 
     /**
      * Checks whether the map contains the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @param key5  the fifth key
      * @return true if the map contains the key
      */
     public boolean containsKey(final Object key1, final Object key2, final Object key3,
                                final Object key4, final Object key5) {
         final int hashCode = hash(key1, key2, key3, key4, key5);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry =
                 decorated().data[decorated().hashIndex(hashCode, decorated().data.length)];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3, key4, key5)) {
                 return true;
             }
             entry = entry.next;
         }
         return false;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     protected AbstractHashedMap<MultiKey<? extends K>, V> decorated() {
         return (AbstractHashedMap<MultiKey<? extends K>, V>) super.decorated();
     }
 
     /**
      * Gets the value mapped to the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @return the mapped value, null if no match
      */
     public V get(final Object key1, final Object key2) {
         final int hashCode = hash(key1, key2);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry =
                 decorated().data[decorated().hashIndex(hashCode, decorated().data.length)];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2)) {
                 return entry.getValue();
             }
             entry = entry.next;
         }
         return null;
     }
 
     /**
      * Gets the value mapped to the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @return the mapped value, null if no match
      */
     public V get(final Object key1, final Object key2, final Object key3) {
         final int hashCode = hash(key1, key2, key3);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry =
                 decorated().data[decorated().hashIndex(hashCode, decorated().data.length)];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3)) {
                 return entry.getValue();
             }
             entry = entry.next;
         }
         return null;
     }
 
     /**
      * Gets the value mapped to the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @return the mapped value, null if no match
      */
     public V get(final Object key1, final Object key2, final Object key3, final Object key4) {
         final int hashCode = hash(key1, key2, key3, key4);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry =
                 decorated().data[decorated().hashIndex(hashCode, decorated().data.length)];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3, key4)) {
                 return entry.getValue();
             }
             entry = entry.next;
         }
         return null;
     }
 
     /**
      * Gets the value mapped to the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @param key5  the fifth key
      * @return the mapped value, null if no match
      */
     public V get(final Object key1, final Object key2, final Object key3, final Object key4, final Object key5) {
         final int hashCode = hash(key1, key2, key3, key4, key5);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry =
                 decorated().data[decorated().hashIndex(hashCode, decorated().data.length)];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3, key4, key5)) {
                 return entry.getValue();
             }
             entry = entry.next;
         }
         return null;
     }
 
     /**
      * Gets the hash code for the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @return the hash code
      */
     protected int hash(final Object key1, final Object key2) {
         int h = 0;
         if (key1 != null) {
             h ^= key1.hashCode();
         }
         if (key2 != null) {
             h ^= key2.hashCode();
         }
         h += ~(h << 9);
         h ^=  h >>> 14;
         h +=  h << 4;
         h ^=  h >>> 10;
         return h;
     }
 
     /**
      * Gets the hash code for the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @return the hash code
      */
     protected int hash(final Object key1, final Object key2, final Object key3) {
         int h = 0;
         if (key1 != null) {
             h ^= key1.hashCode();
         }
         if (key2 != null) {
             h ^= key2.hashCode();
         }
         if (key3 != null) {
             h ^= key3.hashCode();
         }
         h += ~(h << 9);
         h ^=  h >>> 14;
         h +=  h << 4;
         h ^=  h >>> 10;
         return h;
     }
 
     /**
      * Gets the hash code for the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @return the hash code
      */
     protected int hash(final Object key1, final Object key2, final Object key3, final Object key4) {
         int h = 0;
         if (key1 != null) {
             h ^= key1.hashCode();
         }
         if (key2 != null) {
             h ^= key2.hashCode();
         }
         if (key3 != null) {
             h ^= key3.hashCode();
         }
         if (key4 != null) {
             h ^= key4.hashCode();
         }
         h += ~(h << 9);
         h ^=  h >>> 14;
         h +=  h << 4;
         h ^=  h >>> 10;
         return h;
     }
 
     /**
      * Gets the hash code for the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @param key5  the fifth key
      * @return the hash code
      */
     protected int hash(final Object key1, final Object key2, final Object key3, final Object key4, final Object key5) {
         int h = 0;
         if (key1 != null) {
             h ^= key1.hashCode();
         }
         if (key2 != null) {
             h ^= key2.hashCode();
         }
         if (key3 != null) {
             h ^= key3.hashCode();
         }
         if (key4 != null) {
             h ^= key4.hashCode();
         }
         if (key5 != null) {
             h ^= key5.hashCode();
         }
         h += ~(h << 9);
         h ^=  h >>> 14;
         h +=  h << 4;
         h ^=  h >>> 10;
         return h;
     }
 
     /**
      * Is the key equal to the combined key.
      *
      * @param entry  the entry to compare to
      * @param key1  the first key
      * @param key2  the second key
      * @return true if the key matches
      */
     protected boolean isEqualKey(final AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry,
             final Object key1, final Object key2) {
         final MultiKey<? extends K> multi = entry.getKey();
         return
             multi.size() == 2 &&
             (key1 == multi.getKey(0) || key1 != null && key1.equals(multi.getKey(0))) &&
             (key2 == multi.getKey(1) || key2 != null && key2.equals(multi.getKey(1)));
     }
 
     /**
      * Is the key equal to the combined key.
      *
      * @param entry  the entry to compare to
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @return true if the key matches
      */
     protected boolean isEqualKey(final AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry,
                                  final Object key1, final Object key2, final Object key3) {
         final MultiKey<? extends K> multi = entry.getKey();
         return
             multi.size() == 3 &&
             (key1 == multi.getKey(0) || key1 != null && key1.equals(multi.getKey(0))) &&
             (key2 == multi.getKey(1) || key2 != null && key2.equals(multi.getKey(1))) &&
             (key3 == multi.getKey(2) || key3 != null && key3.equals(multi.getKey(2)));
     }
 
     /**
      * Is the key equal to the combined key.
      *
      * @param entry  the entry to compare to
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @return true if the key matches
      */
     protected boolean isEqualKey(final AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry,
                                  final Object key1, final Object key2, final Object key3, final Object key4) {
         final MultiKey<? extends K> multi = entry.getKey();
         return
             multi.size() == 4 &&
             (key1 == multi.getKey(0) || key1 != null && key1.equals(multi.getKey(0))) &&
             (key2 == multi.getKey(1) || key2 != null && key2.equals(multi.getKey(1))) &&
             (key3 == multi.getKey(2) || key3 != null && key3.equals(multi.getKey(2))) &&
             (key4 == multi.getKey(3) || key4 != null && key4.equals(multi.getKey(3)));
     }
 
     /**
      * Is the key equal to the combined key.
      *
      * @param entry  the entry to compare to
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @param key5  the fifth key
      * @return true if the key matches
      */
     protected boolean isEqualKey(final AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry,
             final Object key1, final Object key2, final Object key3, final Object key4, final Object key5) {
         final MultiKey<? extends K> multi = entry.getKey();
         return
             multi.size() == 5 &&
             (key1 == multi.getKey(0) || key1 != null && key1.equals(multi.getKey(0))) &&
             (key2 == multi.getKey(1) || key2 != null && key2.equals(multi.getKey(1))) &&
             (key3 == multi.getKey(2) || key3 != null && key3.equals(multi.getKey(2))) &&
             (key4 == multi.getKey(3) || key4 != null && key4.equals(multi.getKey(3))) &&
             (key5 == multi.getKey(4) || key5 != null && key5.equals(multi.getKey(4)));
     }
 
     @Override
     public MapIterator<MultiKey<? extends K>, V> mapIterator() {
         return decorated().mapIterator();
     }
 
     /**
      * Stores the value against the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @param key5  the fifth key
      * @param value  the value to store
      * @return the value previously mapped to this combined key, null if none
      */
     public V put(final K key1, final K key2, final K key3, final K key4, final K key5, final V value) {
         final int hashCode = hash(key1, key2, key3, key4, key5);
         final int index = decorated().hashIndex(hashCode, decorated().data.length);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry = decorated().data[index];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3, key4, key5)) {
                 final V oldValue = entry.getValue();
                 decorated().updateEntry(entry, value);
                 return oldValue;
             }
             entry = entry.next;
         }
         decorated().addMapping(index, hashCode, new MultiKey<>(key1, key2, key3, key4, key5), value);
         return null;
     }
 
     /**
      * Stores the value against the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @param value  the value to store
      * @return the value previously mapped to this combined key, null if none
      */
     public V put(final K key1, final K key2, final K key3, final K key4, final V value) {
         final int hashCode = hash(key1, key2, key3, key4);
         final int index = decorated().hashIndex(hashCode, decorated().data.length);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry = decorated().data[index];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3, key4)) {
                 final V oldValue = entry.getValue();
                 decorated().updateEntry(entry, value);
                 return oldValue;
             }
             entry = entry.next;
         }
         decorated().addMapping(index, hashCode, new MultiKey<>(key1, key2, key3, key4), value);
         return null;
     }
 
     /**
      * Stores the value against the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param value  the value to store
      * @return the value previously mapped to this combined key, null if none
      */
     public V put(final K key1, final K key2, final K key3, final V value) {
         final int hashCode = hash(key1, key2, key3);
         final int index = decorated().hashIndex(hashCode, decorated().data.length);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry = decorated().data[index];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3)) {
                 final V oldValue = entry.getValue();
                 decorated().updateEntry(entry, value);
                 return oldValue;
             }
             entry = entry.next;
         }
         decorated().addMapping(index, hashCode, new MultiKey<>(key1, key2, key3), value);
         return null;
     }
 
     /**
      * Stores the value against the specified multi-key.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param value  the value to store
      * @return the value previously mapped to this combined key, null if none
      */
     public V put(final K key1, final K key2, final V value) {
         final int hashCode = hash(key1, key2);
         final int index = decorated().hashIndex(hashCode, decorated().data.length);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry = decorated().data[index];
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2)) {
                 final V oldValue = entry.getValue();
                 decorated().updateEntry(entry, value);
                 return oldValue;
             }
             entry = entry.next;
         }
         decorated().addMapping(index, hashCode, new MultiKey<>(key1, key2), value);
         return null;
     }
 
     /**
      * Puts the key and value into the map, where the key must be a non-null
      * MultiKey object.
      *
      * @param key  the non-null MultiKey object
      * @param value  the value to store
      * @return the previous value for the key
      * @throws NullPointerException if the key is null
      * @throws ClassCastException if the key is not a MultiKey
      */
     @Override
     public V put(final MultiKey<? extends K> key, final V value) {
         checkKey(key);
         return super.put(key, value);
     }
 
     /**
      * Copies all of the keys and values from the specified map to this map.
      * Each key must be non-null and a MultiKey object.
      *
      * @param mapToCopy  to this map
      * @throws NullPointerException if the mapToCopy or any key within is null
      * @throws ClassCastException if any key in mapToCopy is not a MultiKey
      */
     @Override
     public void putAll(final Map<? extends MultiKey<? extends K>, ? extends V> mapToCopy) {
         for (final MultiKey<? extends K> key : mapToCopy.keySet()) {
             checkKey(key);
         }
         super.putAll(mapToCopy);
     }
 
     /**
      * Read the map in using a custom routine.
      *
      * @param in  the input stream
      * @throws IOException if an error occurs while reading from the stream
      * @throws ClassNotFoundException if an object read from the stream can not be loaded
      */
     @SuppressWarnings("unchecked")
     private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
         in.defaultReadObject();
         map = (Map<MultiKey<? extends K>, V>) in.readObject();
     }
 
     /**
      * Removes all mappings where the first key is that specified.
      * <p>
      * This method removes all the mappings where the {@code MultiKey}
      * has one or more keys, and the first matches that specified.
      *
      * @param key1  the first key
      * @return true if any elements were removed
      */
     public boolean removeAll(final Object key1) {
         boolean modified = false;
         final MapIterator<MultiKey<? extends K>, V> it = mapIterator();
         while (it.hasNext()) {
             final MultiKey<? extends K> multi = it.next();
             if (multi.size() >= 1 &&
                 (key1 == null ? multi.getKey(0) == null : key1.equals(multi.getKey(0)))) {
                 it.remove();
                 modified = true;
             }
         }
         return modified;
     }
 
     /**
      * Removes all mappings where the first two keys are those specified.
      * <p>
      * This method removes all the mappings where the {@code MultiKey}
      * has two or more keys, and the first two match those specified.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @return true if any elements were removed
      */
     public boolean removeAll(final Object key1, final Object key2) {
         boolean modified = false;
         final MapIterator<MultiKey<? extends K>, V> it = mapIterator();
         while (it.hasNext()) {
             final MultiKey<? extends K> multi = it.next();
             if (multi.size() >= 2 &&
                 (key1 == null ? multi.getKey(0) == null : key1.equals(multi.getKey(0))) &&
                 (key2 == null ? multi.getKey(1) == null : key2.equals(multi.getKey(1)))) {
                 it.remove();
                 modified = true;
             }
         }
         return modified;
     }
 
     /**
      * Removes all mappings where the first three keys are those specified.
      * <p>
      * This method removes all the mappings where the {@code MultiKey}
      * has three or more keys, and the first three match those specified.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @return true if any elements were removed
      */
     public boolean removeAll(final Object key1, final Object key2, final Object key3) {
         boolean modified = false;
         final MapIterator<MultiKey<? extends K>, V> it = mapIterator();
         while (it.hasNext()) {
             final MultiKey<? extends K> multi = it.next();
             if (multi.size() >= 3 &&
                 (key1 == null ? multi.getKey(0) == null : key1.equals(multi.getKey(0))) &&
                 (key2 == null ? multi.getKey(1) == null : key2.equals(multi.getKey(1))) &&
                 (key3 == null ? multi.getKey(2) == null : key3.equals(multi.getKey(2)))) {
                 it.remove();
                 modified = true;
             }
         }
         return modified;
     }
 
     /**
      * Removes all mappings where the first four keys are those specified.
      * <p>
      * This method removes all the mappings where the {@code MultiKey}
      * has four or more keys, and the first four match those specified.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @return true if any elements were removed
      */
     public boolean removeAll(final Object key1, final Object key2, final Object key3, final Object key4) {
         boolean modified = false;
         final MapIterator<MultiKey<? extends K>, V> it = mapIterator();
         while (it.hasNext()) {
             final MultiKey<? extends K> multi = it.next();
             if (multi.size() >= 4 &&
                 (key1 == null ? multi.getKey(0) == null : key1.equals(multi.getKey(0))) &&
                 (key2 == null ? multi.getKey(1) == null : key2.equals(multi.getKey(1))) &&
                 (key3 == null ? multi.getKey(2) == null : key3.equals(multi.getKey(2))) &&
                 (key4 == null ? multi.getKey(3) == null : key4.equals(multi.getKey(3)))) {
                 it.remove();
                 modified = true;
             }
         }
         return modified;
     }
 
     /**
      * Removes the specified multi-key from this map.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @return the value mapped to the removed key, null if key not in map
      * @since 4.0 (previous name: remove(Object, Object))
      */
     public V removeMultiKey(final Object key1, final Object key2) {
         final int hashCode = hash(key1, key2);
         final int index = decorated().hashIndex(hashCode, decorated().data.length);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry = decorated().data[index];
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> previous = null;
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2)) {
                 final V oldValue = entry.getValue();
                 decorated().removeMapping(entry, index, previous);
                 return oldValue;
             }
             previous = entry;
             entry = entry.next;
         }
         return null;
     }
 
     /**
      * Removes the specified multi-key from this map.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @return the value mapped to the removed key, null if key not in map
      * @since 4.0 (previous name: remove(Object, Object, Object))
      */
     public V removeMultiKey(final Object key1, final Object key2, final Object key3) {
         final int hashCode = hash(key1, key2, key3);
         final int index = decorated().hashIndex(hashCode, decorated().data.length);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry = decorated().data[index];
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> previous = null;
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3)) {
                 final V oldValue = entry.getValue();
                 decorated().removeMapping(entry, index, previous);
                 return oldValue;
             }
             previous = entry;
             entry = entry.next;
         }
         return null;
     }
 
     /**
      * Removes the specified multi-key from this map.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @return the value mapped to the removed key, null if key not in map
      * @since 4.0 (previous name: remove(Object, Object, Object, Object))
      */
     public V removeMultiKey(final Object key1, final Object key2, final Object key3, final Object key4) {
         final int hashCode = hash(key1, key2, key3, key4);
         final int index = decorated().hashIndex(hashCode, decorated().data.length);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry = decorated().data[index];
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> previous = null;
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3, key4)) {
                 final V oldValue = entry.getValue();
                 decorated().removeMapping(entry, index, previous);
                 return oldValue;
             }
             previous = entry;
             entry = entry.next;
         }
         return null;
     }
 
     /**
      * Removes the specified multi-key from this map.
      *
      * @param key1  the first key
      * @param key2  the second key
      * @param key3  the third key
      * @param key4  the fourth key
      * @param key5  the fifth key
      * @return the value mapped to the removed key, null if key not in map
      * @since 4.0 (previous name: remove(Object, Object, Object, Object, Object))
      */
     public V removeMultiKey(final Object key1, final Object key2, final Object key3,
                             final Object key4, final Object key5) {
         final int hashCode = hash(key1, key2, key3, key4, key5);
         final int index = decorated().hashIndex(hashCode, decorated().data.length);
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> entry = decorated().data[index];
         AbstractHashedMap.HashEntry<MultiKey<? extends K>, V> previous = null;
         while (entry != null) {
             if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3, key4, key5)) {
                 final V oldValue = entry.getValue();
                 decorated().removeMapping(entry, index, previous);
                 return oldValue;
             }
             previous = entry;
             entry = entry.next;
         }
         return null;
     }
 
     /**
      * Write the map out using a custom routine.
      *
      * @param out  the output stream
      * @throws IOException if an error occurs while writing to the stream
      */
     private void writeObject(final ObjectOutputStream out) throws IOException {
         out.defaultWriteObject();
         out.writeObject(map);
     }
 
 }