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
017 package com.google.common.collect;
018
019 import static com.google.common.base.Preconditions.checkNotNull;
020 import static com.google.common.collect.Iterables.getOnlyElement;
021
022 import com.google.common.annotations.GwtCompatible;
023
024 import java.io.Serializable;
025 import java.util.ArrayList;
026 import java.util.Collections;
027 import java.util.HashMap;
028 import java.util.List;
029 import java.util.Map;
030
031 import javax.annotation.Nullable;
032
033 /**
034 * An immutable, hash-based {@link Map} with reliable user-specified iteration
035 * order. Does not permit null keys or values.
036 *
037 * <p>Unlike {@link Collections#unmodifiableMap}, which is a <i>view</i> of a
038 * separate map which can still change, an instance of {@code ImmutableMap}
039 * contains its own data and will <i>never</i> change. {@code ImmutableMap} is
040 * convenient for {@code public static final} maps ("constant maps") and also
041 * lets you easily make a "defensive copy" of a map provided to your class by a
042 * caller.
043 *
044 * <p><i>Performance notes:</i> unlike {@link HashMap}, {@code ImmutableMap} is
045 * not optimized for element types that have slow {@link Object#equals} or
046 * {@link Object#hashCode} implementations. You can get better performance by
047 * having your element type cache its own hash codes, and by making use of the
048 * cached values to short-circuit a slow {@code equals} algorithm.
049 *
050 * @author Jesse Wilson
051 * @author Kevin Bourrillion
052 * @since 2.0 (imported from Google Collections Library)
053 */
054 @GwtCompatible(serializable = true, emulated = true)
055 @SuppressWarnings("serial") // we're overriding default serialization
056 public abstract class ImmutableMap<K, V> implements Map<K, V>, Serializable {
057 /**
058 * Returns the empty map. This map behaves and performs comparably to
059 * {@link Collections#emptyMap}, and is preferable mainly for consistency
060 * and maintainability of your code.
061 */
062 // Casting to any type is safe because the set will never hold any elements.
063 @SuppressWarnings("unchecked")
064 public static <K, V> ImmutableMap<K, V> of() {
065 return (ImmutableMap<K, V>) EmptyImmutableMap.INSTANCE;
066 }
067
068 /**
069 * Returns an immutable map containing a single entry. This map behaves and
070 * performs comparably to {@link Collections#singletonMap} but will not accept
071 * a null key or value. It is preferable mainly for consistency and
072 * maintainability of your code.
073 */
074 public static <K, V> ImmutableMap<K, V> of(K k1, V v1) {
075 return new SingletonImmutableMap<K, V>(
076 checkNotNull(k1), checkNotNull(v1));
077 }
078
079 /**
080 * Returns an immutable map containing the given entries, in order.
081 *
082 * @throws IllegalArgumentException if duplicate keys are provided
083 */
084 public static <K, V> ImmutableMap<K, V> of(K k1, V v1, K k2, V v2) {
085 return new RegularImmutableMap<K, V>(entryOf(k1, v1), entryOf(k2, v2));
086 }
087
088 /**
089 * Returns an immutable map containing the given entries, in order.
090 *
091 * @throws IllegalArgumentException if duplicate keys are provided
092 */
093 public static <K, V> ImmutableMap<K, V> of(
094 K k1, V v1, K k2, V v2, K k3, V v3) {
095 return new RegularImmutableMap<K, V>(
096 entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3));
097 }
098
099 /**
100 * Returns an immutable map containing the given entries, in order.
101 *
102 * @throws IllegalArgumentException if duplicate keys are provided
103 */
104 public static <K, V> ImmutableMap<K, V> of(
105 K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
106 return new RegularImmutableMap<K, V>(
107 entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4));
108 }
109
110 /**
111 * Returns an immutable map containing the given entries, in order.
112 *
113 * @throws IllegalArgumentException if duplicate keys are provided
114 */
115 public static <K, V> ImmutableMap<K, V> of(
116 K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
117 return new RegularImmutableMap<K, V>(entryOf(k1, v1),
118 entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4), entryOf(k5, v5));
119 }
120
121 // looking for of() with > 5 entries? Use the builder instead.
122
123 /**
124 * Returns a new builder. The generated builder is equivalent to the builder
125 * created by the {@link Builder} constructor.
126 */
127 public static <K, V> Builder<K, V> builder() {
128 return new Builder<K, V>();
129 }
130
131 /**
132 * Verifies that {@code key} and {@code value} are non-null, and returns a new
133 * immutable entry with those values.
134 *
135 * <p>A call to {@link Map.Entry#setValue} on the returned entry will always
136 * throw {@link UnsupportedOperationException}.
137 */
138 static <K, V> Entry<K, V> entryOf(K key, V value) {
139 return Maps.immutableEntry(
140 checkNotNull(key, "null key"),
141 checkNotNull(value, "null value"));
142 }
143
144 /**
145 * A builder for creating immutable map instances, especially {@code public
146 * static final} maps ("constant maps"). Example: <pre> {@code
147 *
148 * static final ImmutableMap<String, Integer> WORD_TO_INT =
149 * new ImmutableMap.Builder<String, Integer>()
150 * .put("one", 1)
151 * .put("two", 2)
152 * .put("three", 3)
153 * .build();}</pre>
154 *
155 * For <i>small</i> immutable maps, the {@code ImmutableMap.of()} methods are
156 * even more convenient.
157 *
158 * <p>Builder instances can be reused - it is safe to call {@link #build}
159 * multiple times to build multiple maps in series. Each map is a superset of
160 * the maps created before it.
161 *
162 * @since 2.0 (imported from Google Collections Library)
163 */
164 public static class Builder<K, V> {
165 final ArrayList<Entry<K, V>> entries = Lists.newArrayList();
166
167 /**
168 * Creates a new builder. The returned builder is equivalent to the builder
169 * generated by {@link ImmutableMap#builder}.
170 */
171 public Builder() {}
172
173 /**
174 * Associates {@code key} with {@code value} in the built map. Duplicate
175 * keys are not allowed, and will cause {@link #build} to fail.
176 */
177 public Builder<K, V> put(K key, V value) {
178 entries.add(entryOf(key, value));
179 return this;
180 }
181
182 /**
183 * Associates all of the given map's keys and values in the built map.
184 * Duplicate keys are not allowed, and will cause {@link #build} to fail.
185 *
186 * @throws NullPointerException if any key or value in {@code map} is null
187 */
188 public Builder<K, V> putAll(Map<? extends K, ? extends V> map) {
189 entries.ensureCapacity(entries.size() + map.size());
190 for (Entry<? extends K, ? extends V> entry : map.entrySet()) {
191 put(entry.getKey(), entry.getValue());
192 }
193 return this;
194 }
195
196 /*
197 * TODO(kevinb): Should build() and the ImmutableBiMap & ImmutableSortedMap
198 * versions throw an IllegalStateException instead?
199 */
200
201 /**
202 * Returns a newly-created immutable map.
203 *
204 * @throws IllegalArgumentException if duplicate keys were added
205 */
206 public ImmutableMap<K, V> build() {
207 return fromEntryList(entries);
208 }
209
210 private static <K, V> ImmutableMap<K, V> fromEntryList(
211 List<Entry<K, V>> entries) {
212 int size = entries.size();
213 switch (size) {
214 case 0:
215 return of();
216 case 1:
217 return new SingletonImmutableMap<K, V>(getOnlyElement(entries));
218 default:
219 Entry<?, ?>[] entryArray
220 = entries.toArray(new Entry<?, ?>[entries.size()]);
221 return new RegularImmutableMap<K, V>(entryArray);
222 }
223 }
224 }
225
226 /**
227 * Returns an immutable map containing the same entries as {@code map}. If
228 * {@code map} somehow contains entries with duplicate keys (for example, if
229 * it is a {@code SortedMap} whose comparator is not <i>consistent with
230 * equals</i>), the results of this method are undefined.
231 *
232 * <p>Despite the method name, this method attempts to avoid actually copying
233 * the data when it is safe to do so. The exact circumstances under which a
234 * copy will or will not be performed are undocumented and subject to change.
235 *
236 * @throws NullPointerException if any key or value in {@code map} is null
237 */
238 public static <K, V> ImmutableMap<K, V> copyOf(
239 Map<? extends K, ? extends V> map) {
240 if ((map instanceof ImmutableMap) && !(map instanceof ImmutableSortedMap)) {
241 // TODO(user): Make ImmutableMap.copyOf(immutableBiMap) call copyOf()
242 // on the ImmutableMap delegate(), rather than the bimap itself
243
244 @SuppressWarnings("unchecked") // safe since map is not writable
245 ImmutableMap<K, V> kvMap = (ImmutableMap<K, V>) map;
246 if (!kvMap.isPartialView()) {
247 return kvMap;
248 }
249 }
250
251 @SuppressWarnings("unchecked") // we won't write to this array
252 Entry<K, V>[] entries = map.entrySet().toArray(new Entry[0]);
253 switch (entries.length) {
254 case 0:
255 return of();
256 case 1:
257 return new SingletonImmutableMap<K, V>(entryOf(
258 entries[0].getKey(), entries[0].getValue()));
259 default:
260 for (int i = 0; i < entries.length; i++) {
261 K k = entries[i].getKey();
262 V v = entries[i].getValue();
263 entries[i] = entryOf(k, v);
264 }
265 return new RegularImmutableMap<K, V>(entries);
266 }
267 }
268
269 ImmutableMap() {}
270
271 /**
272 * Guaranteed to throw an exception and leave the map unmodified.
273 *
274 * @throws UnsupportedOperationException always
275 */
276 @Override
277 public final V put(K k, V v) {
278 throw new UnsupportedOperationException();
279 }
280
281 /**
282 * Guaranteed to throw an exception and leave the map unmodified.
283 *
284 * @throws UnsupportedOperationException always
285 */
286 @Override
287 public final V remove(Object o) {
288 throw new UnsupportedOperationException();
289 }
290
291 /**
292 * Guaranteed to throw an exception and leave the map unmodified.
293 *
294 * @throws UnsupportedOperationException always
295 */
296 @Override
297 public final void putAll(Map<? extends K, ? extends V> map) {
298 throw new UnsupportedOperationException();
299 }
300
301 /**
302 * Guaranteed to throw an exception and leave the map unmodified.
303 *
304 * @throws UnsupportedOperationException always
305 */
306 @Override
307 public final void clear() {
308 throw new UnsupportedOperationException();
309 }
310
311 @Override
312 public boolean isEmpty() {
313 return size() == 0;
314 }
315
316 @Override
317 public boolean containsKey(@Nullable Object key) {
318 return get(key) != null;
319 }
320
321 // Overriding to mark it Nullable
322 @Override
323 public abstract boolean containsValue(@Nullable Object value);
324
325 // Overriding to mark it Nullable
326 @Override
327 public abstract V get(@Nullable Object key);
328
329 /**
330 * Returns an immutable set of the mappings in this map. The entries are in
331 * the same order as the parameters used to build this map.
332 */
333 @Override
334 public abstract ImmutableSet<Entry<K, V>> entrySet();
335
336 /**
337 * Returns an immutable set of the keys in this map. These keys are in
338 * the same order as the parameters used to build this map.
339 */
340 @Override
341 public abstract ImmutableSet<K> keySet();
342
343 /**
344 * Returns an immutable collection of the values in this map. The values are
345 * in the same order as the parameters used to build this map.
346 */
347 @Override
348 public abstract ImmutableCollection<V> values();
349
350 @Override public boolean equals(@Nullable Object object) {
351 if (object == this) {
352 return true;
353 }
354 if (object instanceof Map) {
355 Map<?, ?> that = (Map<?, ?>) object;
356 return this.entrySet().equals(that.entrySet());
357 }
358 return false;
359 }
360
361 abstract boolean isPartialView();
362
363 @Override public int hashCode() {
364 // not caching hash code since it could change if map values are mutable
365 // in a way that modifies their hash codes
366 return entrySet().hashCode();
367 }
368
369 @Override public String toString() {
370 return Maps.toStringImpl(this);
371 }
372
373 /**
374 * Serialized type for all ImmutableMap instances. It captures the logical
375 * contents and they are reconstructed using public factory methods. This
376 * ensures that the implementation types remain as implementation details.
377 */
378 static class SerializedForm implements Serializable {
379 private final Object[] keys;
380 private final Object[] values;
381 SerializedForm(ImmutableMap<?, ?> map) {
382 keys = new Object[map.size()];
383 values = new Object[map.size()];
384 int i = 0;
385 for (Entry<?, ?> entry : map.entrySet()) {
386 keys[i] = entry.getKey();
387 values[i] = entry.getValue();
388 i++;
389 }
390 }
391 Object readResolve() {
392 Builder<Object, Object> builder = new Builder<Object, Object>();
393 return createMap(builder);
394 }
395 Object createMap(Builder<Object, Object> builder) {
396 for (int i = 0; i < keys.length; i++) {
397 builder.put(keys[i], values[i]);
398 }
399 return builder.build();
400 }
401 private static final long serialVersionUID = 0;
402 }
403
404 Object writeReplace() {
405 return new SerializedForm(this);
406 }
407 }