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1   /*
2    * Copyright (C) 2008 The Guava Authors
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    * http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package com.google.common.collect;
18  
19  import static com.google.common.collect.CollectPreconditions.checkNonnegative;
20  
21  import com.google.common.annotations.Beta;
22  import com.google.common.annotations.GwtCompatible;
23  import com.google.errorprone.annotations.CanIgnoreReturnValue;
24  import java.util.Arrays;
25  import java.util.Comparator;
26  import java.util.Map;
27  import java.util.function.Function;
28  import java.util.stream.Collector;
29  import java.util.stream.Collectors;
30  
31  /**
32   * A {@link BiMap} whose contents will never change, with many other important properties detailed
33   * at {@link ImmutableCollection}.
34   *
35   * @author Jared Levy
36   * @since 2.0
37   */
38  @GwtCompatible(serializable = true, emulated = true)
39  public abstract class ImmutableBiMap<K, V> extends ImmutableBiMapFauxverideShim<K, V>
40      implements BiMap<K, V> {
41  
42    /**
43     * Returns a {@link Collector} that accumulates elements into an {@code ImmutableBiMap} whose
44     * keys and values are the result of applying the provided mapping functions to the input
45     * elements. Entries appear in the result {@code ImmutableBiMap} in encounter order.
46     *
47     * <p>If the mapped keys or values contain duplicates
48     * (according to {@link Object#equals(Object)}, an {@code IllegalArgumentException} is thrown
49     * when the collection operation is performed. (This differs from the {@code Collector} returned
50     * by {@link Collectors#toMap(Function, Function)}, which throws an
51     * {@code IllegalStateException}.)
52     *
53     * @since 21.0
54     */
55    @Beta
56    public static <T, K, V> Collector<T, ?, ImmutableBiMap<K, V>> toImmutableBiMap(
57        Function<? super T, ? extends K> keyFunction,
58        Function<? super T, ? extends V> valueFunction) {
59      return CollectCollectors.toImmutableBiMap(keyFunction, valueFunction);
60    }
61  
62    /**
63     * Returns the empty bimap.
64     */
65    // Casting to any type is safe because the set will never hold any elements.
66    @SuppressWarnings("unchecked")
67    public static <K, V> ImmutableBiMap<K, V> of() {
68      return (ImmutableBiMap<K, V>) RegularImmutableBiMap.EMPTY;
69    }
70  
71    /**
72     * Returns an immutable bimap containing a single entry.
73     */
74    public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1) {
75      return new SingletonImmutableBiMap<>(k1, v1);
76    }
77  
78    /**
79     * Returns an immutable map containing the given entries, in order.
80     *
81     * @throws IllegalArgumentException if duplicate keys or values are added
82     */
83    public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2) {
84      return RegularImmutableBiMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2));
85    }
86  
87    /**
88     * Returns an immutable map containing the given entries, in order.
89     *
90     * @throws IllegalArgumentException if duplicate keys or values are added
91     */
92    public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
93      return RegularImmutableBiMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3));
94    }
95  
96    /**
97     * Returns an immutable map containing the given entries, in order.
98     *
99     * @throws IllegalArgumentException if duplicate keys or values are added
100    */
101   public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
102     return RegularImmutableBiMap.fromEntries(
103         entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4));
104   }
105 
106   /**
107    * Returns an immutable map containing the given entries, in order.
108    *
109    * @throws IllegalArgumentException if duplicate keys or values are added
110    */
111   public static <K, V> ImmutableBiMap<K, V> of(
112       K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
113     return RegularImmutableBiMap.fromEntries(
114         entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4), entryOf(k5, v5));
115   }
116 
117   // looking for of() with > 5 entries? Use the builder instead.
118 
119   /**
120    * Returns a new builder. The generated builder is equivalent to the builder
121    * created by the {@link Builder} constructor.
122    */
123   public static <K, V> Builder<K, V> builder() {
124     return new Builder<>();
125   }
126 
127   /**
128    * Returns a new builder, expecting the specified number of entries to be added.
129    *
130    * <p>If {@code expectedSize} is exactly the number of entries added to the builder before {@link
131    * Builder#build} is called, the builder is likely to perform better than an unsized {@link
132    * #builder()} would have.
133    *
134    * <p>It is not specified if any performance benefits apply if {@code expectedSize} is close to,
135    * but not exactly, the number of entries added to the builder.
136    *
137    * @since 23.1
138    */
139   @Beta
140   public static <K, V> Builder<K, V> builderWithExpectedSize(int expectedSize) {
141     checkNonnegative(expectedSize, "expectedSize");
142     return new Builder<>(expectedSize);
143   }
144 
145   /**
146    * A builder for creating immutable bimap instances, especially {@code public
147    * static final} bimaps ("constant bimaps"). Example: <pre>   {@code
148    *
149    *   static final ImmutableBiMap<String, Integer> WORD_TO_INT =
150    *       new ImmutableBiMap.Builder<String, Integer>()
151    *           .put("one", 1)
152    *           .put("two", 2)
153    *           .put("three", 3)
154    *           .build();}</pre>
155    *
156    * <p>For <i>small</i> immutable bimaps, the {@code ImmutableBiMap.of()} methods
157    * are even more convenient.
158    *
159    * <p>By default, a {@code Builder} will generate bimaps that iterate over entries in the order
160    * they were inserted into the builder.  For example, in the above example,
161    * {@code WORD_TO_INT.entrySet()} is guaranteed to iterate over the entries in the order
162    * {@code "one"=1, "two"=2, "three"=3}, and {@code keySet()} and {@code values()} respect the same
163    * order. If you want a different order, consider using
164    * {@link #orderEntriesByValue(Comparator)}, which changes this builder to sort
165    * entries by value.
166    *
167    * <p>Builder instances can be reused - it is safe to call {@link #build}
168    * multiple times to build multiple bimaps in series. Each bimap is a superset
169    * of the bimaps created before it.
170    *
171    * @since 2.0
172    */
173   public static final class Builder<K, V> extends ImmutableMap.Builder<K, V> {
174 
175     /**
176      * Creates a new builder. The returned builder is equivalent to the builder
177      * generated by {@link ImmutableBiMap#builder}.
178      */
179     public Builder() {}
180 
181     Builder(int size) {
182       super(size);
183     }
184 
185     /**
186      * Associates {@code key} with {@code value} in the built bimap. Duplicate
187      * keys or values are not allowed, and will cause {@link #build} to fail.
188      */
189     @CanIgnoreReturnValue
190     @Override
191     public Builder<K, V> put(K key, V value) {
192       super.put(key, value);
193       return this;
194     }
195 
196     /**
197      * Adds the given {@code entry} to the bimap.  Duplicate keys or values
198      * are not allowed, and will cause {@link #build} to fail.
199      *
200      * @since 19.0
201      */
202     @CanIgnoreReturnValue
203     @Override
204     public Builder<K, V> put(Entry<? extends K, ? extends V> entry) {
205       super.put(entry);
206       return this;
207     }
208 
209     /**
210      * Associates all of the given map's keys and values in the built bimap.
211      * Duplicate keys or values are not allowed, and will cause {@link #build}
212      * to fail.
213      *
214      * @throws NullPointerException if any key or value in {@code map} is null
215      */
216     @CanIgnoreReturnValue
217     @Override
218     public Builder<K, V> putAll(Map<? extends K, ? extends V> map) {
219       super.putAll(map);
220       return this;
221     }
222 
223     /**
224      * Adds all of the given entries to the built bimap.  Duplicate keys or
225      * values are not allowed, and will cause {@link #build} to fail.
226      *
227      * @throws NullPointerException if any key, value, or entry is null
228      * @since 19.0
229      */
230     @CanIgnoreReturnValue
231     @Beta
232     @Override
233     public Builder<K, V> putAll(Iterable<? extends Entry<? extends K, ? extends V>> entries) {
234       super.putAll(entries);
235       return this;
236     }
237 
238     /**
239      * Configures this {@code Builder} to order entries by value according to the specified
240      * comparator.
241      *
242      * <p>The sort order is stable, that is, if two entries have values that compare
243      * as equivalent, the entry that was inserted first will be first in the built map's
244      * iteration order.
245      *
246      * @throws IllegalStateException if this method was already called
247      * @since 19.0
248      */
249     @CanIgnoreReturnValue
250     @Beta
251     @Override
252     public Builder<K, V> orderEntriesByValue(Comparator<? super V> valueComparator) {
253       super.orderEntriesByValue(valueComparator);
254       return this;
255     }
256 
257     @Override
258     @CanIgnoreReturnValue
259     Builder<K, V> combine(ImmutableMap.Builder<K, V> builder) {
260       super.combine(builder);
261       return this;
262     }
263 
264     /**
265      * Returns a newly-created immutable bimap.  The iteration order of the returned bimap is
266      * the order in which entries were inserted into the builder, unless
267      * {@link #orderEntriesByValue} was called, in which case entries are sorted by value.
268      *
269      * @throws IllegalArgumentException if duplicate keys or values were added
270      */
271     @Override
272     public ImmutableBiMap<K, V> build() {
273       switch (size) {
274         case 0:
275           return of();
276         case 1:
277           return of(entries[0].getKey(), entries[0].getValue());
278         default:
279           /*
280            * If entries is full, then this implementation may end up using the entries array
281            * directly and writing over the entry objects with non-terminal entries, but this is
282            * safe; if this Builder is used further, it will grow the entries array (so it can't
283            * affect the original array), and future build() calls will always copy any entry
284            * objects that cannot be safely reused.
285            */
286           if (valueComparator != null) {
287             if (entriesUsed) {
288               entries = Arrays.copyOf(entries, size);
289             }
290             Arrays.sort(
291                 entries,
292                 0,
293                 size,
294                 Ordering.from(valueComparator).onResultOf(Maps.<V>valueFunction()));
295           }
296           entriesUsed = size == entries.length;
297           return RegularImmutableBiMap.fromEntryArray(size, entries);
298       }
299     }
300   }
301 
302   /**
303    * Returns an immutable bimap containing the same entries as {@code map}. If
304    * {@code map} somehow contains entries with duplicate keys (for example, if
305    * it is a {@code SortedMap} whose comparator is not <i>consistent with
306    * equals</i>), the results of this method are undefined.
307    *
308    * <p>The returned {@code BiMap} iterates over entries in the same order as the
309    * {@code entrySet} of the original map.
310    *
311    * <p>Despite the method name, this method attempts to avoid actually copying
312    * the data when it is safe to do so. The exact circumstances under which a
313    * copy will or will not be performed are undocumented and subject to change.
314    *
315    * @throws IllegalArgumentException if two keys have the same value or two values have the same
316    *     key
317    * @throws NullPointerException if any key or value in {@code map} is null
318    */
319   public static <K, V> ImmutableBiMap<K, V> copyOf(Map<? extends K, ? extends V> map) {
320     if (map instanceof ImmutableBiMap) {
321       @SuppressWarnings("unchecked") // safe since map is not writable
322       ImmutableBiMap<K, V> bimap = (ImmutableBiMap<K, V>) map;
323       // TODO(lowasser): if we need to make a copy of a BiMap because the
324       // forward map is a view, don't make a copy of the non-view delegate map
325       if (!bimap.isPartialView()) {
326         return bimap;
327       }
328     }
329     return copyOf(map.entrySet());
330   }
331 
332   /**
333    * Returns an immutable bimap containing the given entries.  The returned bimap iterates over
334    * entries in the same order as the original iterable.
335    *
336    * @throws IllegalArgumentException if two keys have the same value or two
337    *         values have the same key
338    * @throws NullPointerException if any key, value, or entry is null
339    * @since 19.0
340    */
341   @Beta
342   public static <K, V> ImmutableBiMap<K, V> copyOf(
343       Iterable<? extends Entry<? extends K, ? extends V>> entries) {
344     @SuppressWarnings("unchecked") // we'll only be using getKey and getValue, which are covariant
345     Entry<K, V>[] entryArray = (Entry<K, V>[]) Iterables.toArray(entries, EMPTY_ENTRY_ARRAY);
346     switch (entryArray.length) {
347       case 0:
348         return of();
349       case 1:
350         Entry<K, V> entry = entryArray[0];
351         return of(entry.getKey(), entry.getValue());
352       default:
353         /*
354          * The current implementation will end up using entryArray directly, though it will write
355          * over the (arbitrary, potentially mutable) Entry objects actually stored in entryArray.
356          */
357         return RegularImmutableBiMap.fromEntries(entryArray);
358     }
359   }
360 
361   ImmutableBiMap() {}
362 
363   /**
364    * {@inheritDoc}
365    *
366    * <p>The inverse of an {@code ImmutableBiMap} is another
367    * {@code ImmutableBiMap}.
368    */
369   @Override
370   public abstract ImmutableBiMap<V, K> inverse();
371 
372   /**
373    * Returns an immutable set of the values in this map, in the same order they appear in {@link
374    * #entrySet}.
375    */
376   @Override
377   public ImmutableSet<V> values() {
378     return inverse().keySet();
379   }
380 
381   @Override
382   final ImmutableSet<V> createValues() {
383     throw new AssertionError("should never be called");
384   }
385 
386   /**
387    * Guaranteed to throw an exception and leave the bimap unmodified.
388    *
389    * @throws UnsupportedOperationException always
390    * @deprecated Unsupported operation.
391    */
392   @CanIgnoreReturnValue
393   @Deprecated
394   @Override
395   public V forcePut(K key, V value) {
396     throw new UnsupportedOperationException();
397   }
398 
399   /**
400    * Serialized type for all ImmutableBiMap instances. It captures the logical
401    * contents and they are reconstructed using public factory methods. This
402    * ensures that the implementation types remain as implementation details.
403    *
404    * Since the bimap is immutable, ImmutableBiMap doesn't require special logic
405    * for keeping the bimap and its inverse in sync during serialization, the way
406    * AbstractBiMap does.
407    */
408   private static class SerializedForm extends ImmutableMap.SerializedForm {
409     SerializedForm(ImmutableBiMap<?, ?> bimap) {
410       super(bimap);
411     }
412 
413     @Override
414     Object readResolve() {
415       Builder<Object, Object> builder = new Builder<>();
416       return createMap(builder);
417     }
418 
419     private static final long serialVersionUID = 0;
420   }
421 
422   @Override
423   Object writeReplace() {
424     return new SerializedForm(this);
425   }
426 }