Java example source code file (LinkedHashMultimap.java)

This example Java source code file (LinkedHashMultimap.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

annotation, collection, default_value_set_capacity, gwtincompatible, iterator, linkedhashmultimap, nullable, object, override, suppresswarnings, util, value_set_load_factor, valueentry, valuesetlink, visiblefortesting

The LinkedHashMultimap.java Java example source code

/*
 * 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.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.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

import javax.annotation.Nullable;

/**
 * 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  {

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

  /**
   * 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 create(int expectedKeys, int expectedValuesPerKey) {
    return new LinkedHashMultimap<K, V>(
        Maps.capacity(expectedKeys), Maps.capacity(expectedValuesPerKey));
  }

  /**
   * 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 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 pred, ValueSetLink succ) {
    pred.setSuccessorInValueSet(succ);
    succ.setPredecessorInValueSet(pred);
  }

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

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

  private static <K, V> void deleteFromMultimap(ValueEntry 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.
   */
  @VisibleForTesting
  static final class ValueEntry<K, V> extends ImmutableEntry implements ValueSetLink {
    final int smearedValueHash;

    @Nullable ValueEntry<K, V> nextInValueBucket;

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

    ValueEntry<K, V> predecessorInMultimap;
    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(new LinkedHashMap<K, Collection(keyCapacity));
    checkNonnegative(valueSetCapacity, "expectedValuesPerKey");

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

  /**
   * {@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 new LinkedHashSet<V>(valueSetCapacity);
  }

  /**
   * {@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}
   *
   * <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 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 {@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<Map.Entry entries() {
    return super.entries();
  }

  /**
   * 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 {
    /*
     * 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;
        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) 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 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) 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) entry;
        deleteFromMultimap(valueEntry);
      }
      succeedsInValueSet(this, this);
      modCount++;
    }
  }

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

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

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

  @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
   */
  @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 (Map.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<K, V>(null, null, 0, null);
    succeedsInMultimap(multimapHeaderEntry, multimapHeaderEntry);
    valueSetCapacity = DEFAULT_VALUE_SET_CAPACITY;
    int distinctKeys = stream.readInt();
    Map<K, Collection map = new LinkedHashMap>();
    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;
}