001 /*
002 * Copyright (C) 2007 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
021 import com.google.common.annotations.GwtCompatible;
022 import com.google.common.base.Preconditions;
023
024 import java.io.InvalidObjectException;
025 import java.io.ObjectInputStream;
026 import java.io.Serializable;
027 import java.util.ArrayList;
028 import java.util.Collection;
029 import java.util.Collections;
030 import java.util.Iterator;
031 import java.util.List;
032 import java.util.RandomAccess;
033
034 import javax.annotation.Nullable;
035
036 /**
037 * A high-performance, immutable, random-access {@code List} implementation.
038 * Does not permit null elements.
039 *
040 * <p>Unlike {@link Collections#unmodifiableList}, which is a <i>view</i> of a
041 * separate collection that can still change, an instance of {@code
042 * ImmutableList} contains its own private data and will <i>never</i> change.
043 * {@code ImmutableList} is convenient for {@code public static final} lists
044 * ("constant lists") and also lets you easily make a "defensive copy" of a list
045 * provided to your class by a caller.
046 *
047 * <p><b>Note:</b> Although this class is not final, it cannot be subclassed as
048 * it has no public or protected constructors. Thus, instances of this type are
049 * guaranteed to be immutable.
050 *
051 * @see ImmutableMap
052 * @see ImmutableSet
053 * @author Kevin Bourrillion
054 * @since 2.0 (imported from Google Collections Library)
055 */
056 @GwtCompatible(serializable = true, emulated = true)
057 @SuppressWarnings("serial") // we're overriding default serialization
058 public abstract class ImmutableList<E> extends ImmutableCollection<E>
059 implements List<E>, RandomAccess {
060 /**
061 * Returns the empty immutable list. This set behaves and performs comparably
062 * to {@link Collections#emptyList}, and is preferable mainly for consistency
063 * and maintainability of your code.
064 */
065 // Casting to any type is safe because the list will never hold any elements.
066 @SuppressWarnings("unchecked")
067 public static <E> ImmutableList<E> of() {
068 return (ImmutableList<E>) EmptyImmutableList.INSTANCE;
069 }
070
071 /**
072 * Returns an immutable list containing a single element. This list behaves
073 * and performs comparably to {@link Collections#singleton}, but will not
074 * accept a null element. It is preferable mainly for consistency and
075 * maintainability of your code.
076 *
077 * @throws NullPointerException if {@code element} is null
078 */
079 public static <E> ImmutableList<E> of(E element) {
080 return new SingletonImmutableList<E>(element);
081 }
082
083 /**
084 * Returns an immutable list containing the given elements, in order.
085 *
086 * @throws NullPointerException if any element is null
087 */
088 public static <E> ImmutableList<E> of(E e1, E e2) {
089 return construct(e1, e2);
090 }
091
092 /**
093 * Returns an immutable list containing the given elements, in order.
094 *
095 * @throws NullPointerException if any element is null
096 */
097 public static <E> ImmutableList<E> of(E e1, E e2, E e3) {
098 return construct(e1, e2, e3);
099 }
100
101 /**
102 * Returns an immutable list containing the given elements, in order.
103 *
104 * @throws NullPointerException if any element is null
105 */
106 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4) {
107 return construct(e1, e2, e3, e4);
108 }
109
110 /**
111 * Returns an immutable list containing the given elements, in order.
112 *
113 * @throws NullPointerException if any element is null
114 */
115 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5) {
116 return construct(e1, e2, e3, e4, e5);
117 }
118
119 /**
120 * Returns an immutable list containing the given elements, in order.
121 *
122 * @throws NullPointerException if any element is null
123 */
124 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6) {
125 return construct(e1, e2, e3, e4, e5, e6);
126 }
127
128 /**
129 * Returns an immutable list containing the given elements, in order.
130 *
131 * @throws NullPointerException if any element is null
132 */
133 public static <E> ImmutableList<E> of(
134 E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
135 return construct(e1, e2, e3, e4, e5, e6, e7);
136 }
137
138 /**
139 * Returns an immutable list containing the given elements, in order.
140 *
141 * @throws NullPointerException if any element is null
142 */
143 public static <E> ImmutableList<E> of(
144 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
145 return construct(e1, e2, e3, e4, e5, e6, e7, e8);
146 }
147
148 /**
149 * Returns an immutable list containing the given elements, in order.
150 *
151 * @throws NullPointerException if any element is null
152 */
153 public static <E> ImmutableList<E> of(
154 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
155 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9);
156 }
157
158 /**
159 * Returns an immutable list containing the given elements, in order.
160 *
161 * @throws NullPointerException if any element is null
162 */
163 public static <E> ImmutableList<E> of(
164 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
165 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10);
166 }
167
168 /**
169 * Returns an immutable list containing the given elements, in order.
170 *
171 * @throws NullPointerException if any element is null
172 */
173 public static <E> ImmutableList<E> of(
174 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11) {
175 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10, e11);
176 }
177
178 // These go up to eleven. After that, you just get the varargs form, and
179 // whatever warnings might come along with it. :(
180
181 /**
182 * Returns an immutable list containing the given elements, in order.
183 *
184 * @throws NullPointerException if any element is null
185 * @since 3.0 (source-compatible since 2.0)
186 */
187 public static <E> ImmutableList<E> of(
188 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11, E e12,
189 E... others) {
190 Object[] array = new Object[12 + others.length];
191 array[0] = e1;
192 array[1] = e2;
193 array[2] = e3;
194 array[3] = e4;
195 array[4] = e5;
196 array[5] = e6;
197 array[6] = e7;
198 array[7] = e8;
199 array[8] = e9;
200 array[9] = e10;
201 array[10] = e11;
202 array[11] = e12;
203 System.arraycopy(others, 0, array, 12, others.length);
204 return construct(array);
205 }
206
207 /**
208 * Returns an immutable list containing the given elements, in order. If
209 * {@code elements} is a {@link Collection}, this method behaves exactly as
210 * {@link #copyOf(Collection)}; otherwise, it behaves exactly as {@code
211 * copyOf(elements.iterator()}.
212 *
213 * @throws NullPointerException if any of {@code elements} is null
214 */
215 public static <E> ImmutableList<E> copyOf(Iterable<? extends E> elements) {
216 checkNotNull(elements); // TODO(kevinb): is this here only for GWT?
217 return (elements instanceof Collection)
218 ? copyOf(Collections2.cast(elements))
219 : copyOf(elements.iterator());
220 }
221
222 /**
223 * Returns an immutable list containing the given elements, in order.
224 *
225 * <p>Despite the method name, this method attempts to avoid actually copying
226 * the data when it is safe to do so. The exact circumstances under which a
227 * copy will or will not be performed are undocumented and subject to change.
228 *
229 * <p>Note that if {@code list} is a {@code List<String>}, then {@code
230 * ImmutableList.copyOf(list)} returns an {@code ImmutableList<String>}
231 * containing each of the strings in {@code list}, while
232 * ImmutableList.of(list)} returns an {@code ImmutableList<List<String>>}
233 * containing one element (the given list itself).
234 *
235 * <p>This method is safe to use even when {@code elements} is a synchronized
236 * or concurrent collection that is currently being modified by another
237 * thread.
238 *
239 * @throws NullPointerException if any of {@code elements} is null
240 */
241 public static <E> ImmutableList<E> copyOf(Collection<? extends E> elements) {
242 if (elements instanceof ImmutableCollection) {
243 @SuppressWarnings("unchecked") // all supported methods are covariant
244 ImmutableList<E> list = ((ImmutableCollection<E>) elements).asList();
245 return list.isPartialView() ? copyFromCollection(list) : list;
246 }
247 return copyFromCollection(elements);
248 }
249
250 /**
251 * Returns an immutable list containing the given elements, in order.
252 *
253 * @throws NullPointerException if any of {@code elements} is null
254 */
255 public static <E> ImmutableList<E> copyOf(Iterator<? extends E> elements) {
256 return copyFromCollection(Lists.newArrayList(elements));
257 }
258
259 /**
260 * Returns an immutable list containing the given elements, in order.
261 *
262 * @throws NullPointerException if any of {@code elements} is null
263 * @since 3.0
264 */
265 public static <E> ImmutableList<E> copyOf(E[] elements) {
266 switch (elements.length) {
267 case 0:
268 return ImmutableList.of();
269 case 1:
270 return new SingletonImmutableList<E>(elements[0]);
271 default:
272 return construct(elements.clone());
273 }
274 }
275
276 private static <E> ImmutableList<E> copyFromCollection(
277 Collection<? extends E> collection) {
278 Object[] elements = collection.toArray();
279 switch (elements.length) {
280 case 0:
281 return of();
282 case 1:
283 @SuppressWarnings("unchecked") // collection had only Es in it
284 ImmutableList<E> list = new SingletonImmutableList<E>((E) elements[0]);
285 return list;
286 default:
287 // safe to use the array without copying it
288 // as specified by Collection.toArray().
289 return construct(elements);
290 }
291 }
292
293 /** {@code elements} has to be internally created array. */
294 private static <E> ImmutableList<E> construct(Object... elements) {
295 for (int i = 0; i < elements.length; i++) {
296 checkElementNotNull(elements[i], i);
297 }
298 return new RegularImmutableList<E>(elements);
299 }
300
301 // We do this instead of Preconditions.checkNotNull to save boxing and array
302 // creation cost.
303 private static Object checkElementNotNull(Object element, int index) {
304 if (element == null) {
305 throw new NullPointerException("at index " + index);
306 }
307 return element;
308 }
309
310 ImmutableList() {}
311
312 // This declaration is needed to make List.iterator() and
313 // ImmutableCollection.iterator() consistent.
314 @Override public UnmodifiableIterator<E> iterator() {
315 return listIterator();
316 }
317
318 @Override public UnmodifiableListIterator<E> listIterator() {
319 return listIterator(0);
320 }
321
322 @Override public abstract UnmodifiableListIterator<E> listIterator(int index);
323
324 // Mark these two methods with @Nullable
325
326 @Override
327 public abstract int indexOf(@Nullable Object object);
328
329 @Override
330 public abstract int lastIndexOf(@Nullable Object object);
331
332 // constrain the return type to ImmutableList<E>
333
334 /**
335 * Returns an immutable list of the elements between the specified {@code
336 * fromIndex}, inclusive, and {@code toIndex}, exclusive. (If {@code
337 * fromIndex} and {@code toIndex} are equal, the empty immutable list is
338 * returned.)
339 */
340 @Override
341 public abstract ImmutableList<E> subList(int fromIndex, int toIndex);
342
343 /**
344 * Guaranteed to throw an exception and leave the list unmodified.
345 *
346 * @throws UnsupportedOperationException always
347 */
348 @Override
349 public final boolean addAll(int index, Collection<? extends E> newElements) {
350 throw new UnsupportedOperationException();
351 }
352
353 /**
354 * Guaranteed to throw an exception and leave the list unmodified.
355 *
356 * @throws UnsupportedOperationException always
357 */
358 @Override
359 public final E set(int index, E element) {
360 throw new UnsupportedOperationException();
361 }
362
363 /**
364 * Guaranteed to throw an exception and leave the list unmodified.
365 *
366 * @throws UnsupportedOperationException always
367 */
368 @Override
369 public final void add(int index, E element) {
370 throw new UnsupportedOperationException();
371 }
372
373 /**
374 * Guaranteed to throw an exception and leave the list unmodified.
375 *
376 * @throws UnsupportedOperationException always
377 */
378 @Override
379 public final E remove(int index) {
380 throw new UnsupportedOperationException();
381 }
382
383 /**
384 * Returns this list instance.
385 *
386 * @since 2.0
387 */
388 @Override public ImmutableList<E> asList() {
389 return this;
390 }
391
392 /**
393 * Returns a view of this immutable list in reverse order. For example, {@code
394 * ImmutableList.of(1, 2, 3).reverse()} is equivalent to {@code
395 * ImmutableList.of(3, 2, 1)}.
396 *
397 * @return a view of this immutable list in reverse order
398 * @since 7.0
399 */
400 public ImmutableList<E> reverse() {
401 return new ReverseImmutableList<E>(this);
402 }
403
404 private static class ReverseImmutableList<E> extends ImmutableList<E> {
405 private transient final ImmutableList<E> forwardList;
406 private transient final int size;
407
408 ReverseImmutableList(ImmutableList<E> backingList) {
409 this.forwardList = backingList;
410 this.size = backingList.size();
411 }
412
413 private int reverseIndex(int index) {
414 return (size - 1) - index;
415 }
416
417 private int reversePosition(int index) {
418 return size - index;
419 }
420
421 @Override public ImmutableList<E> reverse() {
422 return forwardList;
423 }
424
425 @Override public boolean contains(@Nullable Object object) {
426 return forwardList.contains(object);
427 }
428
429 @Override public boolean containsAll(Collection<?> targets) {
430 return forwardList.containsAll(targets);
431 }
432
433 @Override public int indexOf(@Nullable Object object) {
434 int index = forwardList.lastIndexOf(object);
435 return (index >= 0) ? reverseIndex(index) : -1;
436 }
437
438 @Override public int lastIndexOf(@Nullable Object object) {
439 int index = forwardList.indexOf(object);
440 return (index >= 0) ? reverseIndex(index) : -1;
441 }
442
443 @Override public ImmutableList<E> subList(int fromIndex, int toIndex) {
444 Preconditions.checkPositionIndexes(fromIndex, toIndex, size);
445 return forwardList.subList(
446 reversePosition(toIndex), reversePosition(fromIndex)).reverse();
447 }
448
449 @Override public E get(int index) {
450 Preconditions.checkElementIndex(index, size);
451 return forwardList.get(reverseIndex(index));
452 }
453
454 @Override public UnmodifiableListIterator<E> listIterator(int index) {
455 Preconditions.checkPositionIndex(index, size);
456 final UnmodifiableListIterator<E> forward =
457 forwardList.listIterator(reversePosition(index));
458 return new UnmodifiableListIterator<E>() {
459 @Override public boolean hasNext() {
460 return forward.hasPrevious();
461 }
462
463 @Override public boolean hasPrevious() {
464 return forward.hasNext();
465 }
466
467 @Override public E next() {
468 return forward.previous();
469 }
470
471 @Override public int nextIndex() {
472 return reverseIndex(forward.previousIndex());
473 }
474
475 @Override public E previous() {
476 return forward.next();
477 }
478
479 @Override public int previousIndex() {
480 return reverseIndex(forward.nextIndex());
481 }
482 };
483 }
484
485 @Override public int size() {
486 return size;
487 }
488
489 @Override public boolean isEmpty() {
490 return forwardList.isEmpty();
491 }
492
493 @Override boolean isPartialView() {
494 return forwardList.isPartialView();
495 }
496 }
497
498 @Override public boolean equals(Object obj) {
499 return Lists.equalsImpl(this, obj);
500 }
501
502 @Override public int hashCode() {
503 return Lists.hashCodeImpl(this);
504 }
505
506 /*
507 * Serializes ImmutableLists as their logical contents. This ensures that
508 * implementation types do not leak into the serialized representation.
509 */
510 private static class SerializedForm implements Serializable {
511 final Object[] elements;
512 SerializedForm(Object[] elements) {
513 this.elements = elements;
514 }
515 Object readResolve() {
516 return copyOf(elements);
517 }
518 private static final long serialVersionUID = 0;
519 }
520
521 private void readObject(ObjectInputStream stream)
522 throws InvalidObjectException {
523 throw new InvalidObjectException("Use SerializedForm");
524 }
525
526 @Override Object writeReplace() {
527 return new SerializedForm(toArray());
528 }
529
530 /**
531 * Returns a new builder. The generated builder is equivalent to the builder
532 * created by the {@link Builder} constructor.
533 */
534 public static <E> Builder<E> builder() {
535 return new Builder<E>();
536 }
537
538 /**
539 * A builder for creating immutable list instances, especially {@code public
540 * static final} lists ("constant lists"). Example: <pre> {@code
541 *
542 * public static final ImmutableList<Color> GOOGLE_COLORS
543 * = new ImmutableList.Builder<Color>()
544 * .addAll(WEBSAFE_COLORS)
545 * .add(new Color(0, 191, 255))
546 * .build();}</pre>
547 *
548 * Builder instances can be reused; it is safe to call {@link #build} multiple
549 * times to build multiple lists in series. Each new list contains all the
550 * elements of the ones created before it.
551 *
552 * @since 2.0 (imported from Google Collections Library)
553 */
554 public static final class Builder<E> extends ImmutableCollection.Builder<E> {
555 private final ArrayList<E> contents = Lists.newArrayList();
556
557 /**
558 * Creates a new builder. The returned builder is equivalent to the builder
559 * generated by {@link ImmutableList#builder}.
560 */
561 public Builder() {}
562
563 /**
564 * Adds {@code element} to the {@code ImmutableList}.
565 *
566 * @param element the element to add
567 * @return this {@code Builder} object
568 * @throws NullPointerException if {@code element} is null
569 */
570 @Override public Builder<E> add(E element) {
571 contents.add(checkNotNull(element));
572 return this;
573 }
574
575 /**
576 * Adds each element of {@code elements} to the {@code ImmutableList}.
577 *
578 * @param elements the {@code Iterable} to add to the {@code ImmutableList}
579 * @return this {@code Builder} object
580 * @throws NullPointerException if {@code elements} is null or contains a
581 * null element
582 */
583 @Override public Builder<E> addAll(Iterable<? extends E> elements) {
584 if (elements instanceof Collection) {
585 Collection<?> collection = (Collection<?>) elements;
586 contents.ensureCapacity(contents.size() + collection.size());
587 }
588 super.addAll(elements);
589 return this;
590 }
591
592 /**
593 * Adds each element of {@code elements} to the {@code ImmutableList}.
594 *
595 * @param elements the {@code Iterable} to add to the {@code ImmutableList}
596 * @return this {@code Builder} object
597 * @throws NullPointerException if {@code elements} is null or contains a
598 * null element
599 */
600 @Override public Builder<E> add(E... elements) {
601 contents.ensureCapacity(contents.size() + elements.length);
602 super.add(elements);
603 return this;
604 }
605
606 /**
607 * Adds each element of {@code elements} to the {@code ImmutableList}.
608 *
609 * @param elements the {@code Iterable} to add to the {@code ImmutableList}
610 * @return this {@code Builder} object
611 * @throws NullPointerException if {@code elements} is null or contains a
612 * null element
613 */
614 @Override public Builder<E> addAll(Iterator<? extends E> elements) {
615 super.addAll(elements);
616 return this;
617 }
618
619 /**
620 * Returns a newly-created {@code ImmutableList} based on the contents of
621 * the {@code Builder}.
622 */
623 @Override public ImmutableList<E> build() {
624 return copyOf(contents);
625 }
626 }
627 }