common/collect/ImmutableSetMultimap.java

/*
 * Copyright (C) 2009 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 com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.Map.Entry;
import java.util.TreeMap;

import javax.annotation.Nullable;

/**
 * An immutable {@link SetMultimap} with reliable user-specified key and value
 * iteration order. Does not permit null keys or values.
 *
 * <p>Unlike {@link Multimaps#unmodifiableSetMultimap(SetMultimap)}, which is
 * a <i>view</i> of a separate multimap which can still change, an instance of
 * {@code ImmutableSetMultimap} contains its own data and will <i>never</i>
 * change. {@code ImmutableSetMultimap} is convenient for
 * {@code public static final} multimaps ("constant multimaps") and also lets
 * you easily make a "defensive copy" of a multimap provided to your class by
 * a caller.
 *
 * <p><b>Note:</b> Although this class is not final, it cannot be subclassed as
 * it has no public or protected constructors. Thus, instances of this class
 * are guaranteed to be immutable.
 *
 * @author Mike Ward
 * @since 2.0 (imported from Google Collections Library)
 */
@GwtCompatible(serializable = true, emulated = true)
public class ImmutableSetMultimap<K, V>
    extends ImmutableMultimap<K, V>
    implements SetMultimap<K, V> {

  /** Returns the empty multimap. */
  // Casting is safe because the multimap will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableSetMultimap<K, V> of() {
    return (ImmutableSetMultimap<K, V>) EmptyImmutableSetMultimap.INSTANCE;
  }

  /**
   * Returns an immutable multimap containing a single entry.
   */
  public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1) {
    ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
    builder.put(k1, v1);
    return builder.build();
  }

  /**
   * Returns an immutable multimap containing the given entries, in order.
   * Repeated occurrences of an entry (according to {@link Object#equals}) after
   * the first are ignored.
   */
  public static <K, V> ImmutableSetMultimap<K, V> of(K k1, V v1, K k2, V v2) {
    ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
    builder.put(k1, v1);
    builder.put(k2, v2);
    return builder.build();
  }

  /**
   * Returns an immutable multimap containing the given entries, in order.
   * Repeated occurrences of an entry (according to {@link Object#equals}) after
   * the first are ignored.
   */
  public static <K, V> ImmutableSetMultimap<K, V> of(
      K k1, V v1, K k2, V v2, K k3, V v3) {
    ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
    builder.put(k1, v1);
    builder.put(k2, v2);
    builder.put(k3, v3);
    return builder.build();
  }

  /**
   * Returns an immutable multimap containing the given entries, in order.
   * Repeated occurrences of an entry (according to {@link Object#equals}) after
   * the first are ignored.
   */
  public static <K, V> ImmutableSetMultimap<K, V> of(
      K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
    ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
    builder.put(k1, v1);
    builder.put(k2, v2);
    builder.put(k3, v3);
    builder.put(k4, v4);
    return builder.build();
  }

  /**
   * Returns an immutable multimap containing the given entries, in order.
   * Repeated occurrences of an entry (according to {@link Object#equals}) after
   * the first are ignored.
   */
  public static <K, V> ImmutableSetMultimap<K, V> of(
      K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
    ImmutableSetMultimap.Builder<K, V> builder = ImmutableSetMultimap.builder();
    builder.put(k1, v1);
    builder.put(k2, v2);
    builder.put(k3, v3);
    builder.put(k4, v4);
    builder.put(k5, v5);
    return builder.build();
  }

  // looking for of() with > 5 entries? Use the builder instead.

  /**
   * Returns a new {@link Builder}.
   */
  public static <K, V> Builder<K, V> builder() {
    return new Builder<K, V>();
  }

  /**
   * Multimap for {@link ImmutableSetMultimap.Builder} that maintains key
   * and value orderings and performs better than {@link LinkedHashMultimap}.
   */
  private static class BuilderMultimap<K, V> extends AbstractMultimap<K, V> {
    BuilderMultimap() {
      super(new LinkedHashMap<K, Collection<V>>());
    }
    @Override Collection<V> createCollection() {
      return Sets.newLinkedHashSet();
    }
    private static final long serialVersionUID = 0;
  }

  /**
   * Multimap for {@link ImmutableSetMultimap.Builder} that sorts keys and
   * maintains value orderings.
   */
  private static class SortedKeyBuilderMultimap<K, V>
      extends AbstractMultimap<K, V> {
    SortedKeyBuilderMultimap(
        Comparator<? super K> keyComparator, Multimap<K, V> multimap) {
      super(new TreeMap<K, Collection<V>>(keyComparator));
      putAll(multimap);
    }
    @Override Collection<V> createCollection() {
      return Sets.newLinkedHashSet();
    }
    private static final long serialVersionUID = 0;
  }

  /**
   * A builder for creating immutable {@code SetMultimap} instances, especially
   * {@code public static final} multimaps ("constant multimaps"). Example:
   * <pre>   {@code
   *
   *   static final Multimap<String, Integer> STRING_TO_INTEGER_MULTIMAP =
   *       new ImmutableSetMultimap.Builder<String, Integer>()
   *           .put("one", 1)
   *           .putAll("several", 1, 2, 3)
   *           .putAll("many", 1, 2, 3, 4, 5)
   *           .build();}</pre>
   *
   * Builder instances can be reused; it is safe to call {@link #build} multiple
   * times to build multiple multimaps in series. Each multimap contains the
   * key-value mappings in the previously created multimaps.
   *
   * @since 2.0 (imported from Google Collections Library)
   */
  public static final class Builder<K, V>
      extends ImmutableMultimap.Builder<K, V> {
    /**
     * Creates a new builder. The returned builder is equivalent to the builder
     * generated by {@link ImmutableSetMultimap#builder}.
     */
    public Builder() {
      builderMultimap = new BuilderMultimap<K, V>();
    }

    /**
     * Adds a key-value mapping to the built multimap if it is not already
     * present.
     */
    @Override public Builder<K, V> put(K key, V value) {
      builderMultimap.put(checkNotNull(key), checkNotNull(value));
      return this;
    }

    /**
     * Adds an entry to the built multimap if it is not already present.
     *
     * @since 11.0
     */
    @Override public Builder<K, V> put(Entry<? extends K, ? extends V> entry) {
      builderMultimap.put(
          checkNotNull(entry.getKey()), checkNotNull(entry.getValue()));
      return this;
    }

    @Override public Builder<K, V> putAll(K key, Iterable<? extends V> values) {
      Collection<V> collection = builderMultimap.get(checkNotNull(key));
      for (V value : values) {
        collection.add(checkNotNull(value));
      }
      return this;
    }

    @Override public Builder<K, V> putAll(K key, V... values) {
      return putAll(key, Arrays.asList(values));
    }

    @Override public Builder<K, V> putAll(
        Multimap<? extends K, ? extends V> multimap) {
      for (Entry<? extends K, ? extends Collection<? extends V>> entry
          : multimap.asMap().entrySet()) {
        putAll(entry.getKey(), entry.getValue());
      }
      return this;
    }

    /**
     * {@inheritDoc}
     *
     * @since 8.0
     */
    @Beta @Override
    public Builder<K, V> orderKeysBy(Comparator<? super K> keyComparator) {
      builderMultimap = new SortedKeyBuilderMultimap<K, V>(
          checkNotNull(keyComparator), builderMultimap);
      return this;
    }

    /**
     * Specifies the ordering of the generated multimap's values for each key.
     *
     * <p>If this method is called, the sets returned by the {@code get()}
     * method of the generated multimap and its {@link Multimap#asMap()} view
     * are {@link ImmutableSortedSet} instances. However, serialization does not
     * preserve that property, though it does maintain the key and value
     * ordering.
     *
     * @since 8.0
     */
    // TODO: Make serialization behavior consistent.
    @Beta @Override
    public Builder<K, V> orderValuesBy(Comparator<? super V> valueComparator) {
      super.orderValuesBy(valueComparator);
      return this;
    }

    /**
     * Returns a newly-created immutable set multimap.
     */
    @Override public ImmutableSetMultimap<K, V> build() {
      return copyOf(builderMultimap, valueComparator);
    }
  }

  /**
   * Returns an immutable set multimap containing the same mappings as
   * {@code multimap}. The generated multimap's key and value orderings
   * correspond to the iteration ordering of the {@code multimap.asMap()} view.
   * Repeated occurrences of an entry in the multimap after the first are
   * ignored.
   *
   * <p>Despite the method name, this method attempts to avoid actually copying
   * the data when it is safe to do so. The exact circumstances under which a
   * copy will or will not be performed are undocumented and subject to change.
   *
   * @throws NullPointerException if any key or value in {@code multimap} is
   *     null
   */
  public static <K, V> ImmutableSetMultimap<K, V> copyOf(
      Multimap<? extends K, ? extends V> multimap) {
    return copyOf(multimap, null);
  }

  private static <K, V> ImmutableSetMultimap<K, V> copyOf(
      Multimap<? extends K, ? extends V> multimap,
      Comparator<? super V> valueComparator) {
    checkNotNull(multimap); // eager for GWT
    if (multimap.isEmpty() && valueComparator == null) {
      return of();
    }

    if (multimap instanceof ImmutableSetMultimap) {
      @SuppressWarnings("unchecked") // safe since multimap is not writable
      ImmutableSetMultimap<K, V> kvMultimap
          = (ImmutableSetMultimap<K, V>) multimap;
      if (!kvMultimap.isPartialView()) {
        return kvMultimap;
      }
    }

    ImmutableMap.Builder<K, ImmutableSet<V>> builder = ImmutableMap.builder();
    int size = 0;

    for (Entry<? extends K, ? extends Collection<? extends V>> entry
        : multimap.asMap().entrySet()) {
      K key = entry.getKey();
      Collection<? extends V> values = entry.getValue();
      ImmutableSet<V> set = (valueComparator == null)
          ? ImmutableSet.copyOf(values)
          : ImmutableSortedSet.copyOf(valueComparator, values);
      if (!set.isEmpty()) {
        builder.put(key, set);
        size += set.size();
      }
    }

    return new ImmutableSetMultimap<K, V>(
        builder.build(), size, valueComparator);
  }

  // Returned by get() when values are sorted and a missing key is provided.
  private final transient ImmutableSortedSet<V> emptySet;

  ImmutableSetMultimap(ImmutableMap<K, ImmutableSet<V>> map, int size,
      @Nullable Comparator<? super V> valueComparator) {
    super(map, size);
    this.emptySet = (valueComparator == null)
        ? null : ImmutableSortedSet.<V>emptySet(valueComparator);
  }

  // views

  /**
   * Returns an immutable set of the values for the given key.  If no mappings
   * in the multimap have the provided key, an empty immutable set is returned.
   * The values are in the same order as the parameters used to build this
   * multimap.
   */
  @Override public ImmutableSet<V> get(@Nullable K key) {
    // This cast is safe as its type is known in constructor.
    ImmutableSet<V> set = (ImmutableSet<V>) map.get(key);
    if (set != null) {
      return set;
    } else if (emptySet != null) {
      return emptySet;
    } else {
      return ImmutableSet.<V>of();
    }
  }

  private transient ImmutableSetMultimap<V, K> inverse;

  /**
   * {@inheritDoc}
   *
   * <p>Because an inverse of a set multimap cannot contain multiple pairs with the same key and
   * value, this method returns an {@code ImmutableSetMultimap} rather than the
   * {@code ImmutableMultimap} specified in the {@code ImmutableMultimap} class.
   *
   * @since 11
   */
  @Beta
  public ImmutableSetMultimap<V, K> inverse() {
    ImmutableSetMultimap<V, K> result = inverse;
    return (result == null) ? (inverse = invert()) : result;
  }

  private ImmutableSetMultimap<V, K> invert() {
    Builder<V, K> builder = builder();
    for (Entry<K, V> entry : entries()) {
      builder.put(entry.getValue(), entry.getKey());
    }
    ImmutableSetMultimap<V, K> invertedMultimap = builder.build();
    invertedMultimap.inverse = this;
    return invertedMultimap;
  }

  /**
   * Guaranteed to throw an exception and leave the multimap unmodified.
   *
   * @throws UnsupportedOperationException always
   */
  @Override public ImmutableSet<V> removeAll(Object key) {
    throw new UnsupportedOperationException();
  }

  /**
   * Guaranteed to throw an exception and leave the multimap unmodified.
   *
   * @throws UnsupportedOperationException always
   */
  @Override public ImmutableSet<V> replaceValues(
      K key, Iterable<? extends V> values) {
    throw new UnsupportedOperationException();
  }

  private transient ImmutableSet<Entry<K, V>> entries;

  /**
   * Returns an immutable collection of all key-value pairs in the multimap.
   * Its iterator traverses the values for the first key, the values for the
   * second key, and so on.
   */
  // TODO(kevinb): Fix this so that two copies of the entries are not created.
  @Override public ImmutableSet<Entry<K, V>> entries() {
    ImmutableSet<Entry<K, V>> result = entries;
    return (result == null)
        ? (entries = ImmutableSet.copyOf(super.entries()))
        : result;
  }
}