com.google.guava/guava/27.1-jre : com/google/common/collect/LinkedHashMultimap.java

LinkedHashMultimap
https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more.
The Apache Software License, Version 2.0
Kevin Bourrillion (Google)
/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed 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 com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;
import static com.google.common.collect.CollectPreconditions.checkRemove;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Objects;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.j2objc.annotations.WeakOuter;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Arrays;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
import org.checkerframework.checker.nullness.qual.Nullable;

Implementation of Multimap that does not allow duplicate key-value entries and that returns collections whose iterators follow the ordering in which the data was added to the multimap. The collections returned by keySet, keys, and asMap iterate through the keys in the order they were first added to the multimap. Similarly, get, 
removeAll, and replaceValues return collections that iterate through the values in the order they were added. The collections generated by entries and values iterate across the key-value mappings in the order they were added to the multimap. 
The iteration ordering of the collections generated by keySet, keys, and asMap has a few subtleties. As long as the set of keys remains unchanged, adding or removing mappings does not affect the key iteration order. However, if you remove all values associated with a key and then add the key back to the multimap, that key will come last in the key iteration order. 
The multimap does not store duplicate key-value pairs. Adding a new key-value pair equal to an
existing key-value pair has no effect.
Keys and values may be null. All optional multimap methods are supported, and all returned
views are modifiable.
This class is not threadsafe when any concurrent operations update the multimap. Concurrent read operations will work correctly. To allow concurrent update operations, wrap your multimap with a call to Multimaps.synchronizedSetMultimap. 
See the Guava User Guide article on  
Multimap.
Author: Jared Levy, Louis Wasserman
Since: 2.0/**
 * Implementation of {@code Multimap} that does not allow duplicate key-value entries and that
 * returns collections whose iterators follow the ordering in which the data was added to the
 * multimap.
 *
 * <p>The collections returned by {@code keySet}, {@code keys}, and {@code asMap} iterate through
 * the keys in the order they were first added to the multimap. Similarly, {@code get}, {@code
 * removeAll}, and {@code replaceValues} return collections that iterate through the values in the
 * order they were added. The collections generated by {@code entries} and {@code values} iterate
 * across the key-value mappings in the order they were added to the multimap.
 *
 * <p>The iteration ordering of the collections generated by {@code keySet}, {@code keys}, and
 * {@code asMap} has a few subtleties. As long as the set of keys remains unchanged, adding or
 * removing mappings does not affect the key iteration order. However, if you remove all values
 * associated with a key and then add the key back to the multimap, that key will come last in the
 * key iteration order.
 *
 * <p>The multimap does not store duplicate key-value pairs. Adding a new key-value pair equal to an
 * existing key-value pair has no effect.
 *
 * <p>Keys and values may be null. All optional multimap methods are supported, and all returned
 * views are modifiable.
 *
 * <p>This class is not threadsafe when any concurrent operations update the multimap. Concurrent
 * read operations will work correctly. To allow concurrent update operations, wrap your multimap
 * with a call to {@link Multimaps#synchronizedSetMultimap}.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multimap"> {@code
 * Multimap}</a>.
 *
 * @author Jared Levy
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible(serializable = true, emulated = true)
public final class LinkedHashMultimap<K, V>
    extends LinkedHashMultimapGwtSerializationDependencies<K, V> {

  Creates a new, empty LinkedHashMultimap with the default initial capacities. /** Creates a new, empty {@code LinkedHashMultimap} with the default initial capacities. */
  public static <K, V> LinkedHashMultimap<K, V> create() {
    return new LinkedHashMultimap<>(DEFAULT_KEY_CAPACITY, DEFAULT_VALUE_SET_CAPACITY);
  }

  Constructs an empty LinkedHashMultimap with enough capacity to hold the specified numbers of keys and values without rehashing. 
Params: expectedKeys – the expected number of distinct keys
expectedValuesPerKey – the expected average number of values per key
Throws: IllegalArgumentException – if expectedKeys or expectedValuesPerKey is negative/**
   * Constructs an empty {@code LinkedHashMultimap} with enough capacity to hold the specified
   * numbers of keys and values without rehashing.
   *
   * @param expectedKeys the expected number of distinct keys
   * @param expectedValuesPerKey the expected average number of values per key
   * @throws IllegalArgumentException if {@code expectedKeys} or {@code expectedValuesPerKey} is
   *     negative
   */
  public static <K, V> LinkedHashMultimap<K, V> create(int expectedKeys, int expectedValuesPerKey) {
    return new LinkedHashMultimap<>(
        Maps.capacity(expectedKeys), Maps.capacity(expectedValuesPerKey));
  }

  Constructs a LinkedHashMultimap with the same mappings as the specified multimap. If a key-value mapping appears multiple times in the input multimap, it only appears once in the constructed multimap. The new multimap has the same Multimap.entries() iteration order as the input multimap, except for excluding duplicate mappings. 
Params: multimap – the multimap whose contents are copied to this multimap/**
   * Constructs a {@code LinkedHashMultimap} with the same mappings as the specified multimap. If a
   * key-value mapping appears multiple times in the input multimap, it only appears once in the
   * constructed multimap. The new multimap has the same {@link Multimap#entries()} iteration order
   * as the input multimap, except for excluding duplicate mappings.
   *
   * @param multimap the multimap whose contents are copied to this multimap
   */
  public static <K, V> LinkedHashMultimap<K, V> create(
      Multimap<? extends K, ? extends V> multimap) {
    LinkedHashMultimap<K, V> result = create(multimap.keySet().size(), DEFAULT_VALUE_SET_CAPACITY);
    result.putAll(multimap);
    return result;
  }

  private interface ValueSetLink<K, V> {
    ValueSetLink<K, V> getPredecessorInValueSet();

    ValueSetLink<K, V> getSuccessorInValueSet();

    void setPredecessorInValueSet(ValueSetLink<K, V> entry);

    void setSuccessorInValueSet(ValueSetLink<K, V> entry);
  }

  private static <K, V> void succeedsInValueSet(ValueSetLink<K, V> pred, ValueSetLink<K, V> succ) {
    pred.setSuccessorInValueSet(succ);
    succ.setPredecessorInValueSet(pred);
  }

  private static <K, V> void succeedsInMultimap(ValueEntry<K, V> pred, ValueEntry<K, V> succ) {
    pred.setSuccessorInMultimap(succ);
    succ.setPredecessorInMultimap(pred);
  }

  private static <K, V> void deleteFromValueSet(ValueSetLink<K, V> entry) {
    succeedsInValueSet(entry.getPredecessorInValueSet(), entry.getSuccessorInValueSet());
  }

  private static <K, V> void deleteFromMultimap(ValueEntry<K, V> entry) {
    succeedsInMultimap(entry.getPredecessorInMultimap(), entry.getSuccessorInMultimap());
  }

  LinkedHashMultimap entries are in no less than three coexisting linked lists: a bucket in the hash table for a Set<V> associated with a key, the linked list of insertion-ordered entries in that Set<V>, and the linked list of entries in the LinkedHashMultimap as a whole. /**
   * LinkedHashMultimap entries are in no less than three coexisting linked lists: a bucket in the
   * hash table for a {@code Set<V>} associated with a key, the linked list of insertion-ordered
   * entries in that {@code Set<V>}, and the linked list of entries in the LinkedHashMultimap as a
   * whole.
   */
  @VisibleForTesting
  static final class ValueEntry<K, V> extends ImmutableEntry<K, V> implements ValueSetLink<K, V> {
    final int smearedValueHash;

    @Nullable ValueEntry<K, V> nextInValueBucket;

    @Nullable ValueSetLink<K, V> predecessorInValueSet;
    @Nullable ValueSetLink<K, V> successorInValueSet;

    @Nullable ValueEntry<K, V> predecessorInMultimap;
    @Nullable ValueEntry<K, V> successorInMultimap;

    ValueEntry(
        @Nullable K key,
        @Nullable V value,
        int smearedValueHash,
        @Nullable ValueEntry<K, V> nextInValueBucket) {
      super(key, value);
      this.smearedValueHash = smearedValueHash;
      this.nextInValueBucket = nextInValueBucket;
    }

    boolean matchesValue(@Nullable Object v, int smearedVHash) {
      return smearedValueHash == smearedVHash && Objects.equal(getValue(), v);
    }

    @Override
    public ValueSetLink<K, V> getPredecessorInValueSet() {
      return predecessorInValueSet;
    }

    @Override
    public ValueSetLink<K, V> getSuccessorInValueSet() {
      return successorInValueSet;
    }

    @Override
    public void setPredecessorInValueSet(ValueSetLink<K, V> entry) {
      predecessorInValueSet = entry;
    }

    @Override
    public void setSuccessorInValueSet(ValueSetLink<K, V> entry) {
      successorInValueSet = entry;
    }

    public ValueEntry<K, V> getPredecessorInMultimap() {
      return predecessorInMultimap;
    }

    public ValueEntry<K, V> getSuccessorInMultimap() {
      return successorInMultimap;
    }

    public void setSuccessorInMultimap(ValueEntry<K, V> multimapSuccessor) {
      this.successorInMultimap = multimapSuccessor;
    }

    public void setPredecessorInMultimap(ValueEntry<K, V> multimapPredecessor) {
      this.predecessorInMultimap = multimapPredecessor;
    }
  }

  private static final int DEFAULT_KEY_CAPACITY = 16;
  private static final int DEFAULT_VALUE_SET_CAPACITY = 2;
  @VisibleForTesting static final double VALUE_SET_LOAD_FACTOR = 1.0;

  @VisibleForTesting transient int valueSetCapacity = DEFAULT_VALUE_SET_CAPACITY;
  private transient ValueEntry<K, V> multimapHeaderEntry;

  private LinkedHashMultimap(int keyCapacity, int valueSetCapacity) {
    super(Platform.<K, Collection<V>>newLinkedHashMapWithExpectedSize(keyCapacity));
    checkNonnegative(valueSetCapacity, "expectedValuesPerKey");

    this.valueSetCapacity = valueSetCapacity;
    this.multimapHeaderEntry = new ValueEntry<>(null, null, 0, null);
    succeedsInMultimap(multimapHeaderEntry, multimapHeaderEntry);
  }

  {@inheritDoc}
Creates an empty LinkedHashSet for a collection of values for one key. 
Returns: a new LinkedHashSet containing a collection of values for one key/**
   * {@inheritDoc}
   *
   * <p>Creates an empty {@code LinkedHashSet} for a collection of values for one key.
   *
   * @return a new {@code LinkedHashSet} containing a collection of values for one key
   */
  @Override
  Set<V> createCollection() {
    return Platform.newLinkedHashSetWithExpectedSize(valueSetCapacity);
  }

  {@inheritDoc}
Creates a decorated insertion-ordered set that also keeps track of the order in which
key-value pairs are added to the multimap.
Params: key – key to associate with values in the collection
Returns: a new decorated set containing a collection of values for one key/**
   * {@inheritDoc}
   *
   * <p>Creates a decorated insertion-ordered set that also keeps track of the order in which
   * key-value pairs are added to the multimap.
   *
   * @param key key to associate with values in the collection
   * @return a new decorated set containing a collection of values for one key
   */
  @Override
  Collection<V> createCollection(K key) {
    return new ValueSet(key, valueSetCapacity);
  }

  {@inheritDoc}
If values is not empty and the multimap already contains a mapping for key, the keySet() ordering is unchanged. However, the provided values always come last in the entries() and values() iteration orderings. /**
   * {@inheritDoc}
   *
   * <p>If {@code values} is not empty and the multimap already contains a mapping for {@code key},
   * the {@code keySet()} ordering is unchanged. However, the provided values always come last in
   * the {@link #entries()} and {@link #values()} iteration orderings.
   */
  @CanIgnoreReturnValue
  @Override
  public Set<V> replaceValues(@Nullable K key, Iterable<? extends V> values) {
    return super.replaceValues(key, values);
  }

  Returns a set of all key-value pairs. Changes to the returned set will update the underlying multimap, and vice versa. The entries set does not support the add or addAll operations. The iterator generated by the returned set traverses the entries in the order they were
added to the multimap.
Each entry is an immutable snapshot of a key-value mapping in the multimap, taken at the
time the entry is returned by a method call to the collection or its iterator.
/**
   * Returns a set of all key-value pairs. Changes to the returned set will update the underlying
   * multimap, and vice versa. The entries set does not support the {@code add} or {@code addAll}
   * operations.
   *
   * <p>The iterator generated by the returned set traverses the entries in the order they were
   * added to the multimap.
   *
   * <p>Each entry is an immutable snapshot of a key-value mapping in the multimap, taken at the
   * time the entry is returned by a method call to the collection or its iterator.
   */
  @Override
  public Set<Entry<K, V>> entries() {
    return super.entries();
  }

  Returns a view collection of all distinct keys contained in this multimap. Note that the
key set contains a key if and only if this multimap maps that key to at least one value.
The iterator generated by the returned set traverses the keys in the order they were first
added to the multimap.
Changes to the returned set will update the underlying multimap, and vice versa. However,
adding to the returned set is not possible.
/**
   * Returns a view collection of all <i>distinct</i> keys contained in this multimap. Note that the
   * key set contains a key if and only if this multimap maps that key to at least one value.
   *
   * <p>The iterator generated by the returned set traverses the keys in the order they were first
   * added to the multimap.
   *
   * <p>Changes to the returned set will update the underlying multimap, and vice versa. However,
   * <i>adding</i> to the returned set is not possible.
   */
  @Override
  public Set<K> keySet() {
    return super.keySet();
  }

  Returns a collection of all values in the multimap. Changes to the returned collection will
update the underlying multimap, and vice versa.
The iterator generated by the returned collection traverses the values in the order they
were added to the multimap.
/**
   * Returns a collection of all values in the multimap. Changes to the returned collection will
   * update the underlying multimap, and vice versa.
   *
   * <p>The iterator generated by the returned collection traverses the values in the order they
   * were added to the multimap.
   */
  @Override
  public Collection<V> values() {
    return super.values();
  }

  @VisibleForTesting
  @WeakOuter
  final class ValueSet extends Sets.ImprovedAbstractSet<V> implements ValueSetLink<K, V> {
    /*
     * We currently use a fixed load factor of 1.0, a bit higher than normal to reduce memory
     * consumption.
     */

    private final K key;
    @VisibleForTesting ValueEntry<K, V>[] hashTable;
    private int size = 0;
    private int modCount = 0;

    // We use the set object itself as the end of the linked list, avoiding an unnecessary
    // entry object per key.
    private ValueSetLink<K, V> firstEntry;
    private ValueSetLink<K, V> lastEntry;

    ValueSet(K key, int expectedValues) {
      this.key = key;
      this.firstEntry = this;
      this.lastEntry = this;
      // Round expected values up to a power of 2 to get the table size.
      int tableSize = Hashing.closedTableSize(expectedValues, VALUE_SET_LOAD_FACTOR);

      @SuppressWarnings("unchecked")
      ValueEntry<K, V>[] hashTable = new ValueEntry[tableSize];
      this.hashTable = hashTable;
    }

    private int mask() {
      return hashTable.length - 1;
    }

    @Override
    public ValueSetLink<K, V> getPredecessorInValueSet() {
      return lastEntry;
    }

    @Override
    public ValueSetLink<K, V> getSuccessorInValueSet() {
      return firstEntry;
    }

    @Override
    public void setPredecessorInValueSet(ValueSetLink<K, V> entry) {
      lastEntry = entry;
    }

    @Override
    public void setSuccessorInValueSet(ValueSetLink<K, V> entry) {
      firstEntry = entry;
    }

    @Override
    public Iterator<V> iterator() {
      return new Iterator<V>() {
        ValueSetLink<K, V> nextEntry = firstEntry;
        @Nullable ValueEntry<K, V> toRemove;
        int expectedModCount = modCount;

        private void checkForComodification() {
          if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();
          }
        }

        @Override
        public boolean hasNext() {
          checkForComodification();
          return nextEntry != ValueSet.this;
        }

        @Override
        public V next() {
          if (!hasNext()) {
            throw new NoSuchElementException();
          }
          ValueEntry<K, V> entry = (ValueEntry<K, V>) nextEntry;
          V result = entry.getValue();
          toRemove = entry;
          nextEntry = entry.getSuccessorInValueSet();
          return result;
        }

        @Override
        public void remove() {
          checkForComodification();
          checkRemove(toRemove != null);
          ValueSet.this.remove(toRemove.getValue());
          expectedModCount = modCount;
          toRemove = null;
        }
      };
    }

    @Override
    public void forEach(Consumer<? super V> action) {
      checkNotNull(action);
      for (ValueSetLink<K, V> entry = firstEntry;
          entry != ValueSet.this;
          entry = entry.getSuccessorInValueSet()) {
        action.accept(((ValueEntry<K, V>) entry).getValue());
      }
    }

    @Override
    public int size() {
      return size;
    }

    @Override
    public boolean contains(@Nullable Object o) {
      int smearedHash = Hashing.smearedHash(o);
      for (ValueEntry<K, V> entry = hashTable[smearedHash & mask()];
          entry != null;
          entry = entry.nextInValueBucket) {
        if (entry.matchesValue(o, smearedHash)) {
          return true;
        }
      }
      return false;
    }

    @Override
    public boolean add(@Nullable V value) {
      int smearedHash = Hashing.smearedHash(value);
      int bucket = smearedHash & mask();
      ValueEntry<K, V> rowHead = hashTable[bucket];
      for (ValueEntry<K, V> entry = rowHead; entry != null; entry = entry.nextInValueBucket) {
        if (entry.matchesValue(value, smearedHash)) {
          return false;
        }
      }

      ValueEntry<K, V> newEntry = new ValueEntry<>(key, value, smearedHash, rowHead);
      succeedsInValueSet(lastEntry, newEntry);
      succeedsInValueSet(newEntry, this);
      succeedsInMultimap(multimapHeaderEntry.getPredecessorInMultimap(), newEntry);
      succeedsInMultimap(newEntry, multimapHeaderEntry);
      hashTable[bucket] = newEntry;
      size++;
      modCount++;
      rehashIfNecessary();
      return true;
    }

    private void rehashIfNecessary() {
      if (Hashing.needsResizing(size, hashTable.length, VALUE_SET_LOAD_FACTOR)) {
        @SuppressWarnings("unchecked")
        ValueEntry<K, V>[] hashTable = new ValueEntry[this.hashTable.length * 2];
        this.hashTable = hashTable;
        int mask = hashTable.length - 1;
        for (ValueSetLink<K, V> entry = firstEntry;
            entry != this;
            entry = entry.getSuccessorInValueSet()) {
          ValueEntry<K, V> valueEntry = (ValueEntry<K, V>) entry;
          int bucket = valueEntry.smearedValueHash & mask;
          valueEntry.nextInValueBucket = hashTable[bucket];
          hashTable[bucket] = valueEntry;
        }
      }
    }

    @CanIgnoreReturnValue
    @Override
    public boolean remove(@Nullable Object o) {
      int smearedHash = Hashing.smearedHash(o);
      int bucket = smearedHash & mask();
      ValueEntry<K, V> prev = null;
      for (ValueEntry<K, V> entry = hashTable[bucket];
          entry != null;
          prev = entry, entry = entry.nextInValueBucket) {
        if (entry.matchesValue(o, smearedHash)) {
          if (prev == null) {
            // first entry in the bucket
            hashTable[bucket] = entry.nextInValueBucket;
          } else {
            prev.nextInValueBucket = entry.nextInValueBucket;
          }
          deleteFromValueSet(entry);
          deleteFromMultimap(entry);
          size--;
          modCount++;
          return true;
        }
      }
      return false;
    }

    @Override
    public void clear() {
      Arrays.fill(hashTable, null);
      size = 0;
      for (ValueSetLink<K, V> entry = firstEntry;
          entry != this;
          entry = entry.getSuccessorInValueSet()) {
        ValueEntry<K, V> valueEntry = (ValueEntry<K, V>) entry;
        deleteFromMultimap(valueEntry);
      }
      succeedsInValueSet(this, this);
      modCount++;
    }
  }

  @Override
  Iterator<Entry<K, V>> entryIterator() {
    return new Iterator<Entry<K, V>>() {
      ValueEntry<K, V> nextEntry = multimapHeaderEntry.successorInMultimap;
      @Nullable ValueEntry<K, V> toRemove;

      @Override
      public boolean hasNext() {
        return nextEntry != multimapHeaderEntry;
      }

      @Override
      public Entry<K, V> next() {
        if (!hasNext()) {
          throw new NoSuchElementException();
        }
        ValueEntry<K, V> result = nextEntry;
        toRemove = result;
        nextEntry = nextEntry.successorInMultimap;
        return result;
      }

      @Override
      public void remove() {
        checkRemove(toRemove != null);
        LinkedHashMultimap.this.remove(toRemove.getKey(), toRemove.getValue());
        toRemove = null;
      }
    };
  }

  @Override
  Spliterator<Entry<K, V>> entrySpliterator() {
    return Spliterators.spliterator(entries(), Spliterator.DISTINCT | Spliterator.ORDERED);
  }

  @Override
  Iterator<V> valueIterator() {
    return Maps.valueIterator(entryIterator());
  }

  @Override
  Spliterator<V> valueSpliterator() {
    return CollectSpliterators.map(entrySpliterator(), Entry::getValue);
  }

  @Override
  public void clear() {
    super.clear();
    succeedsInMultimap(multimapHeaderEntry, multimapHeaderEntry);
  }

  @serialData the expected values per key, the number of distinct keys, the number of entries,
    and the entries in order/**
   * @serialData the expected values per key, the number of distinct keys, the number of entries,
   *     and the entries in order
   */
  @GwtIncompatible // java.io.ObjectOutputStream
  private void writeObject(ObjectOutputStream stream) throws IOException {
    stream.defaultWriteObject();
    stream.writeInt(keySet().size());
    for (K key : keySet()) {
      stream.writeObject(key);
    }
    stream.writeInt(size());
    for (Entry<K, V> entry : entries()) {
      stream.writeObject(entry.getKey());
      stream.writeObject(entry.getValue());
    }
  }

  @GwtIncompatible // java.io.ObjectInputStream
  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
    stream.defaultReadObject();
    multimapHeaderEntry = new ValueEntry<>(null, null, 0, null);
    succeedsInMultimap(multimapHeaderEntry, multimapHeaderEntry);
    valueSetCapacity = DEFAULT_VALUE_SET_CAPACITY;
    int distinctKeys = stream.readInt();
    Map<K, Collection<V>> map = Platform.newLinkedHashMapWithExpectedSize(12);
    for (int i = 0; i < distinctKeys; i++) {
      @SuppressWarnings("unchecked")
      K key = (K) stream.readObject();
      map.put(key, createCollection(key));
    }
    int entries = stream.readInt();
    for (int i = 0; i < entries; i++) {
      @SuppressWarnings("unchecked")
      K key = (K) stream.readObject();
      @SuppressWarnings("unchecked")
      V value = (V) stream.readObject();
      map.get(key).add(value);
    }
    setMap(map);
  }

  @GwtIncompatible // java serialization not supported
  private static final long serialVersionUID = 1;
}
Params:	expectedKeys – the expected number of distinct keys expectedValuesPerKey – the expected average number of values per key
Throws:	IllegalArgumentException – if `expectedKeys` or `expectedValuesPerKey` is negative
Params:	key – key to associate with values in the collection
Returns:	a new decorated set containing a collection of values for one key
/

com.google.guava/ guava/ 27.1-jre/ com/google/common/collect/LinkedHashMultimap.java
