001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect;
018
019import static com.google.common.base.Preconditions.checkState;
020import static com.google.common.collect.CollectPreconditions.checkNonnegative;
021
022import com.google.common.annotations.Beta;
023import com.google.common.annotations.GwtCompatible;
024import com.google.common.annotations.VisibleForTesting;
025import com.google.errorprone.annotations.CanIgnoreReturnValue;
026import java.util.Arrays;
027import java.util.Comparator;
028import java.util.Map;
029import java.util.function.Function;
030import java.util.stream.Collector;
031import java.util.stream.Collectors;
032
033/**
034 * A {@link BiMap} whose contents will never change, with many other important properties detailed
035 * at {@link ImmutableCollection}.
036 *
037 * @author Jared Levy
038 * @since 2.0
039 */
040@GwtCompatible(serializable = true, emulated = true)
041public abstract class ImmutableBiMap<K, V> extends ImmutableBiMapFauxverideShim<K, V>
042    implements BiMap<K, V> {
043
044  /**
045   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableBiMap} whose keys
046   * and values are the result of applying the provided mapping functions to the input elements.
047   * Entries appear in the result {@code ImmutableBiMap} in encounter order.
048   *
049   * <p>If the mapped keys or values contain duplicates (according to {@link Object#equals(Object)},
050   * an {@code IllegalArgumentException} is thrown when the collection operation is performed. (This
051   * differs from the {@code Collector} returned by {@link Collectors#toMap(Function, Function)},
052   * which throws an {@code IllegalStateException}.)
053   *
054   * @since 21.0
055   */
056  @Beta
057  public static <T, K, V> Collector<T, ?, ImmutableBiMap<K, V>> toImmutableBiMap(
058      Function<? super T, ? extends K> keyFunction,
059      Function<? super T, ? extends V> valueFunction) {
060    return CollectCollectors.toImmutableBiMap(keyFunction, valueFunction);
061  }
062
063  /** Returns the empty bimap. */
064  // Casting to any type is safe because the set will never hold any elements.
065  @SuppressWarnings("unchecked")
066  public static <K, V> ImmutableBiMap<K, V> of() {
067    return (ImmutableBiMap<K, V>) RegularImmutableBiMap.EMPTY;
068  }
069
070  /** Returns an immutable bimap containing a single entry. */
071  public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1) {
072    return new SingletonImmutableBiMap<>(k1, v1);
073  }
074
075  /**
076   * Returns an immutable map containing the given entries, in order.
077   *
078   * @throws IllegalArgumentException if duplicate keys or values are added
079   */
080  public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2) {
081    return RegularImmutableBiMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2));
082  }
083
084  /**
085   * Returns an immutable map containing the given entries, in order.
086   *
087   * @throws IllegalArgumentException if duplicate keys or values are added
088   */
089  public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
090    return RegularImmutableBiMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3));
091  }
092
093  /**
094   * Returns an immutable map containing the given entries, in order.
095   *
096   * @throws IllegalArgumentException if duplicate keys or values are added
097   */
098  public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
099    return RegularImmutableBiMap.fromEntries(
100        entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4));
101  }
102
103  /**
104   * Returns an immutable map containing the given entries, in order.
105   *
106   * @throws IllegalArgumentException if duplicate keys or values are added
107   */
108  public static <K, V> ImmutableBiMap<K, V> of(
109      K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
110    return RegularImmutableBiMap.fromEntries(
111        entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4), entryOf(k5, v5));
112  }
113
114  // looking for of() with > 5 entries? Use the builder instead.
115
116  /**
117   * Returns a new builder. The generated builder is equivalent to the builder created by the {@link
118   * Builder} constructor.
119   */
120  public static <K, V> Builder<K, V> builder() {
121    return new Builder<>();
122  }
123
124  /**
125   * Returns a new builder, expecting the specified number of entries to be added.
126   *
127   * <p>If {@code expectedSize} is exactly the number of entries added to the builder before {@link
128   * Builder#build} is called, the builder is likely to perform better than an unsized {@link
129   * #builder()} would have.
130   *
131   * <p>It is not specified if any performance benefits apply if {@code expectedSize} is close to,
132   * but not exactly, the number of entries added to the builder.
133   *
134   * @since 23.1
135   */
136  @Beta
137  public static <K, V> Builder<K, V> builderWithExpectedSize(int expectedSize) {
138    checkNonnegative(expectedSize, "expectedSize");
139    return new Builder<>(expectedSize);
140  }
141
142  /**
143   * A builder for creating immutable bimap instances, especially {@code public static final} bimaps
144   * ("constant bimaps"). Example:
145   *
146   * <pre>{@code
147   * static final ImmutableBiMap<String, Integer> WORD_TO_INT =
148   *     new ImmutableBiMap.Builder<String, Integer>()
149   *         .put("one", 1)
150   *         .put("two", 2)
151   *         .put("three", 3)
152   *         .build();
153   * }</pre>
154   *
155   * <p>For <i>small</i> immutable bimaps, the {@code ImmutableBiMap.of()} methods are even more
156   * convenient.
157   *
158   * <p>By default, a {@code Builder} will generate bimaps that iterate over entries in the order
159   * they were inserted into the builder. For example, in the above example, {@code
160   * WORD_TO_INT.entrySet()} is guaranteed to iterate over the entries in the order {@code "one"=1,
161   * "two"=2, "three"=3}, and {@code keySet()} and {@code values()} respect the same order. If you
162   * want a different order, consider using {@link #orderEntriesByValue(Comparator)}, which changes
163   * this builder to sort entries by value.
164   *
165   * <p>Builder instances can be reused - it is safe to call {@link #build} multiple times to build
166   * multiple bimaps in series. Each bimap is a superset of the bimaps created before it.
167   *
168   * @since 2.0
169   */
170  public static final class Builder<K, V> extends ImmutableMap.Builder<K, V> {
171
172    /**
173     * Creates a new builder. The returned builder is equivalent to the builder generated by {@link
174     * ImmutableBiMap#builder}.
175     */
176    public Builder() {}
177
178    Builder(int size) {
179      super(size);
180    }
181
182    /**
183     * Associates {@code key} with {@code value} in the built bimap. Duplicate keys or values are
184     * not allowed, and will cause {@link #build} to fail.
185     */
186    @CanIgnoreReturnValue
187    @Override
188    public Builder<K, V> put(K key, V value) {
189      super.put(key, value);
190      return this;
191    }
192
193    /**
194     * Adds the given {@code entry} to the bimap. Duplicate keys or values are not allowed, and will
195     * cause {@link #build} to fail.
196     *
197     * @since 19.0
198     */
199    @CanIgnoreReturnValue
200    @Override
201    public Builder<K, V> put(Entry<? extends K, ? extends V> entry) {
202      super.put(entry);
203      return this;
204    }
205
206    /**
207     * Associates all of the given map's keys and values in the built bimap. Duplicate keys or
208     * values are not allowed, and will cause {@link #build} to fail.
209     *
210     * @throws NullPointerException if any key or value in {@code map} is null
211     */
212    @CanIgnoreReturnValue
213    @Override
214    public Builder<K, V> putAll(Map<? extends K, ? extends V> map) {
215      super.putAll(map);
216      return this;
217    }
218
219    /**
220     * Adds all of the given entries to the built bimap. Duplicate keys or values are not allowed,
221     * and will cause {@link #build} to fail.
222     *
223     * @throws NullPointerException if any key, value, or entry is null
224     * @since 19.0
225     */
226    @CanIgnoreReturnValue
227    @Beta
228    @Override
229    public Builder<K, V> putAll(Iterable<? extends Entry<? extends K, ? extends V>> entries) {
230      super.putAll(entries);
231      return this;
232    }
233
234    /**
235     * Configures this {@code Builder} to order entries by value according to the specified
236     * comparator.
237     *
238     * <p>The sort order is stable, that is, if two entries have values that compare as equivalent,
239     * the entry that was inserted first will be first in the built map's iteration order.
240     *
241     * @throws IllegalStateException if this method was already called
242     * @since 19.0
243     */
244    @CanIgnoreReturnValue
245    @Beta
246    @Override
247    public Builder<K, V> orderEntriesByValue(Comparator<? super V> valueComparator) {
248      super.orderEntriesByValue(valueComparator);
249      return this;
250    }
251
252    @Override
253    @CanIgnoreReturnValue
254    Builder<K, V> combine(ImmutableMap.Builder<K, V> builder) {
255      super.combine(builder);
256      return this;
257    }
258
259    /**
260     * Returns a newly-created immutable bimap. The iteration order of the returned bimap is the
261     * order in which entries were inserted into the builder, unless {@link #orderEntriesByValue}
262     * was called, in which case entries are sorted by value.
263     *
264     * @throws IllegalArgumentException if duplicate keys or values were added
265     */
266    @Override
267    public ImmutableBiMap<K, V> build() {
268      switch (size) {
269        case 0:
270          return of();
271        case 1:
272          return of(entries[0].getKey(), entries[0].getValue());
273        default:
274          /*
275           * If entries is full, or if hash flooding is detected, then this implementation may end
276           * up using the entries array directly and writing over the entry objects with
277           * non-terminal entries, but this is safe; if this Builder is used further, it will grow
278           * the entries array (so it can't affect the original array), and future build() calls
279           * will always copy any entry objects that cannot be safely reused.
280           */
281          if (valueComparator != null) {
282            if (entriesUsed) {
283              entries = Arrays.copyOf(entries, size);
284            }
285            Arrays.sort(
286                entries,
287                0,
288                size,
289                Ordering.from(valueComparator).onResultOf(Maps.<V>valueFunction()));
290          }
291          entriesUsed = true;
292          return RegularImmutableBiMap.fromEntryArray(size, entries);
293      }
294    }
295
296    @Override
297    @VisibleForTesting
298    ImmutableBiMap<K, V> buildJdkBacked() {
299      checkState(
300          valueComparator == null,
301          "buildJdkBacked is for tests only, doesn't support orderEntriesByValue");
302      switch (size) {
303        case 0:
304          return of();
305        case 1:
306          return of(entries[0].getKey(), entries[0].getValue());
307        default:
308          entriesUsed = true;
309          return RegularImmutableBiMap.fromEntryArray(size, entries);
310      }
311    }
312  }
313
314  /**
315   * Returns an immutable bimap containing the same entries as {@code map}. If {@code map} somehow
316   * contains entries with duplicate keys (for example, if it is a {@code SortedMap} whose
317   * comparator is not <i>consistent with equals</i>), the results of this method are undefined.
318   *
319   * <p>The returned {@code BiMap} iterates over entries in the same order as the {@code entrySet}
320   * of the original map.
321   *
322   * <p>Despite the method name, this method attempts to avoid actually copying the data when it is
323   * safe to do so. The exact circumstances under which a copy will or will not be performed are
324   * undocumented and subject to change.
325   *
326   * @throws IllegalArgumentException if two keys have the same value or two values have the same
327   *     key
328   * @throws NullPointerException if any key or value in {@code map} is null
329   */
330  public static <K, V> ImmutableBiMap<K, V> copyOf(Map<? extends K, ? extends V> map) {
331    if (map instanceof ImmutableBiMap) {
332      @SuppressWarnings("unchecked") // safe since map is not writable
333      ImmutableBiMap<K, V> bimap = (ImmutableBiMap<K, V>) map;
334      // TODO(lowasser): if we need to make a copy of a BiMap because the
335      // forward map is a view, don't make a copy of the non-view delegate map
336      if (!bimap.isPartialView()) {
337        return bimap;
338      }
339    }
340    return copyOf(map.entrySet());
341  }
342
343  /**
344   * Returns an immutable bimap containing the given entries. The returned bimap iterates over
345   * entries in the same order as the original iterable.
346   *
347   * @throws IllegalArgumentException if two keys have the same value or two values have the same
348   *     key
349   * @throws NullPointerException if any key, value, or entry is null
350   * @since 19.0
351   */
352  @Beta
353  public static <K, V> ImmutableBiMap<K, V> copyOf(
354      Iterable<? extends Entry<? extends K, ? extends V>> entries) {
355    @SuppressWarnings("unchecked") // we'll only be using getKey and getValue, which are covariant
356    Entry<K, V>[] entryArray = (Entry<K, V>[]) Iterables.toArray(entries, EMPTY_ENTRY_ARRAY);
357    switch (entryArray.length) {
358      case 0:
359        return of();
360      case 1:
361        Entry<K, V> entry = entryArray[0];
362        return of(entry.getKey(), entry.getValue());
363      default:
364        /*
365         * The current implementation will end up using entryArray directly, though it will write
366         * over the (arbitrary, potentially mutable) Entry objects actually stored in entryArray.
367         */
368        return RegularImmutableBiMap.fromEntries(entryArray);
369    }
370  }
371
372  ImmutableBiMap() {}
373
374  /**
375   * {@inheritDoc}
376   *
377   * <p>The inverse of an {@code ImmutableBiMap} is another {@code ImmutableBiMap}.
378   */
379  @Override
380  public abstract ImmutableBiMap<V, K> inverse();
381
382  /**
383   * Returns an immutable set of the values in this map, in the same order they appear in {@link
384   * #entrySet}.
385   */
386  @Override
387  public ImmutableSet<V> values() {
388    return inverse().keySet();
389  }
390
391  @Override
392  final ImmutableSet<V> createValues() {
393    throw new AssertionError("should never be called");
394  }
395
396  /**
397   * Guaranteed to throw an exception and leave the bimap unmodified.
398   *
399   * @throws UnsupportedOperationException always
400   * @deprecated Unsupported operation.
401   */
402  @CanIgnoreReturnValue
403  @Deprecated
404  @Override
405  public V forcePut(K key, V value) {
406    throw new UnsupportedOperationException();
407  }
408
409  /**
410   * Serialized type for all ImmutableBiMap instances. It captures the logical contents and they are
411   * reconstructed using public factory methods. This ensures that the implementation types remain
412   * as implementation details.
413   *
414   * <p>Since the bimap is immutable, ImmutableBiMap doesn't require special logic for keeping the
415   * bimap and its inverse in sync during serialization, the way AbstractBiMap does.
416   */
417  private static class SerializedForm extends ImmutableMap.SerializedForm {
418    SerializedForm(ImmutableBiMap<?, ?> bimap) {
419      super(bimap);
420    }
421
422    @Override
423    Object readResolve() {
424      Builder<Object, Object> builder = new Builder<>();
425      return createMap(builder);
426    }
427
428    private static final long serialVersionUID = 0;
429  }
430
431  @Override
432  Object writeReplace() {
433    return new SerializedForm(this);
434  }
435}