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.checkElementIndex;
020 import static com.google.common.base.Preconditions.checkNotNull;
021 import static com.google.common.base.Preconditions.checkPositionIndex;
022 import static com.google.common.base.Preconditions.checkPositionIndexes;
023
024 import com.google.common.annotations.GwtCompatible;
025
026 import java.io.InvalidObjectException;
027 import java.io.ObjectInputStream;
028 import java.io.Serializable;
029 import java.util.ArrayList;
030 import java.util.Collection;
031 import java.util.Collections;
032 import java.util.Iterator;
033 import java.util.List;
034 import java.util.RandomAccess;
035
036 import javax.annotation.Nullable;
037
038 /**
039 * A high-performance, immutable, random-access {@code List} implementation.
040 * Does not permit null elements.
041 *
042 * <p>Unlike {@link Collections#unmodifiableList}, which is a <i>view</i> of a
043 * separate collection that can still change, an instance of {@code
044 * ImmutableList} contains its own private data and will <i>never</i> change.
045 * {@code ImmutableList} is convenient for {@code public static final} lists
046 * ("constant lists") and also lets you easily make a "defensive copy" of a list
047 * provided to your class by a caller.
048 *
049 * <p><b>Note:</b> Although this class is not final, it cannot be subclassed as
050 * it has no public or protected constructors. Thus, instances of this type are
051 * guaranteed to be immutable.
052 *
053 * <p>See the Guava User Guide article on <a href=
054 * "http://code.google.com/p/guava-libraries/wiki/ImmutableCollectionsExplained">
055 * immutable collections</a>.
056 *
057 * @see ImmutableMap
058 * @see ImmutableSet
059 * @author Kevin Bourrillion
060 * @since 2.0 (imported from Google Collections Library)
061 */
062 @GwtCompatible(serializable = true, emulated = true)
063 @SuppressWarnings("serial") // we're overriding default serialization
064 public abstract class ImmutableList<E> extends ImmutableCollection<E>
065 implements List<E>, RandomAccess {
066 /**
067 * Returns the empty immutable list. This set behaves and performs comparably
068 * to {@link Collections#emptyList}, and is preferable mainly for consistency
069 * and maintainability of your code.
070 */
071 // Casting to any type is safe because the list will never hold any elements.
072 @SuppressWarnings("unchecked")
073 public static <E> ImmutableList<E> of() {
074 return (ImmutableList<E>) EmptyImmutableList.INSTANCE;
075 }
076
077 /**
078 * Returns an immutable list containing a single element. This list behaves
079 * and performs comparably to {@link Collections#singleton}, but will not
080 * accept a null element. It is preferable mainly for consistency and
081 * maintainability of your code.
082 *
083 * @throws NullPointerException if {@code element} is null
084 */
085 public static <E> ImmutableList<E> of(E element) {
086 return new SingletonImmutableList<E>(element);
087 }
088
089 /**
090 * Returns an immutable list containing the given elements, in order.
091 *
092 * @throws NullPointerException if any element is null
093 */
094 public static <E> ImmutableList<E> of(E e1, E e2) {
095 return construct(e1, e2);
096 }
097
098 /**
099 * Returns an immutable list containing the given elements, in order.
100 *
101 * @throws NullPointerException if any element is null
102 */
103 public static <E> ImmutableList<E> of(E e1, E e2, E e3) {
104 return construct(e1, e2, e3);
105 }
106
107 /**
108 * Returns an immutable list containing the given elements, in order.
109 *
110 * @throws NullPointerException if any element is null
111 */
112 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4) {
113 return construct(e1, e2, e3, e4);
114 }
115
116 /**
117 * Returns an immutable list containing the given elements, in order.
118 *
119 * @throws NullPointerException if any element is null
120 */
121 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5) {
122 return construct(e1, e2, e3, e4, e5);
123 }
124
125 /**
126 * Returns an immutable list containing the given elements, in order.
127 *
128 * @throws NullPointerException if any element is null
129 */
130 public static <E> ImmutableList<E> of(E e1, E e2, E e3, E e4, E e5, E e6) {
131 return construct(e1, e2, e3, e4, e5, e6);
132 }
133
134 /**
135 * Returns an immutable list containing the given elements, in order.
136 *
137 * @throws NullPointerException if any element is null
138 */
139 public static <E> ImmutableList<E> of(
140 E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
141 return construct(e1, e2, e3, e4, e5, e6, e7);
142 }
143
144 /**
145 * Returns an immutable list containing the given elements, in order.
146 *
147 * @throws NullPointerException if any element is null
148 */
149 public static <E> ImmutableList<E> of(
150 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
151 return construct(e1, e2, e3, e4, e5, e6, e7, e8);
152 }
153
154 /**
155 * Returns an immutable list containing the given elements, in order.
156 *
157 * @throws NullPointerException if any element is null
158 */
159 public static <E> ImmutableList<E> of(
160 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
161 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9);
162 }
163
164 /**
165 * Returns an immutable list containing the given elements, in order.
166 *
167 * @throws NullPointerException if any element is null
168 */
169 public static <E> ImmutableList<E> of(
170 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
171 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10);
172 }
173
174 /**
175 * Returns an immutable list containing the given elements, in order.
176 *
177 * @throws NullPointerException if any element is null
178 */
179 public static <E> ImmutableList<E> of(
180 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11) {
181 return construct(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10, e11);
182 }
183
184 // These go up to eleven. After that, you just get the varargs form, and
185 // whatever warnings might come along with it. :(
186
187 /**
188 * Returns an immutable list containing the given elements, in order.
189 *
190 * @throws NullPointerException if any element is null
191 * @since 3.0 (source-compatible since 2.0)
192 */
193 public static <E> ImmutableList<E> of(
194 E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10, E e11, E e12,
195 E... others) {
196 Object[] array = new Object[12 + others.length];
197 array[0] = e1;
198 array[1] = e2;
199 array[2] = e3;
200 array[3] = e4;
201 array[4] = e5;
202 array[5] = e6;
203 array[6] = e7;
204 array[7] = e8;
205 array[8] = e9;
206 array[9] = e10;
207 array[10] = e11;
208 array[11] = e12;
209 System.arraycopy(others, 0, array, 12, others.length);
210 return construct(array);
211 }
212
213 /**
214 * Returns an immutable list containing the given elements, in order. If
215 * {@code elements} is a {@link Collection}, this method behaves exactly as
216 * {@link #copyOf(Collection)}; otherwise, it behaves exactly as {@code
217 * copyOf(elements.iterator()}.
218 *
219 * @throws NullPointerException if any of {@code elements} is null
220 */
221 public static <E> ImmutableList<E> copyOf(Iterable<? extends E> elements) {
222 checkNotNull(elements); // TODO(kevinb): is this here only for GWT?
223 return (elements instanceof Collection)
224 ? copyOf(Collections2.cast(elements))
225 : copyOf(elements.iterator());
226 }
227
228 /**
229 * Returns an immutable list containing the given elements, in order.
230 *
231 * <p>Despite the method name, this method attempts to avoid actually copying
232 * the data when it is safe to do so. The exact circumstances under which a
233 * copy will or will not be performed are undocumented and subject to change.
234 *
235 * <p>Note that if {@code list} is a {@code List<String>}, then {@code
236 * ImmutableList.copyOf(list)} returns an {@code ImmutableList<String>}
237 * containing each of the strings in {@code list}, while
238 * ImmutableList.of(list)} returns an {@code ImmutableList<List<String>>}
239 * containing one element (the given list itself).
240 *
241 * <p>This method is safe to use even when {@code elements} is a synchronized
242 * or concurrent collection that is currently being modified by another
243 * thread.
244 *
245 * @throws NullPointerException if any of {@code elements} is null
246 */
247 public static <E> ImmutableList<E> copyOf(Collection<? extends E> elements) {
248 if (elements instanceof ImmutableCollection) {
249 @SuppressWarnings("unchecked") // all supported methods are covariant
250 ImmutableList<E> list = ((ImmutableCollection<E>) elements).asList();
251 return list.isPartialView() ? copyFromCollection(list) : list;
252 }
253 return copyFromCollection(elements);
254 }
255
256 /**
257 * Returns an immutable list containing the given elements, in order.
258 *
259 * @throws NullPointerException if any of {@code elements} is null
260 */
261 public static <E> ImmutableList<E> copyOf(Iterator<? extends E> elements) {
262 return copyFromCollection(Lists.newArrayList(elements));
263 }
264
265 /**
266 * Returns an immutable list containing the given elements, in order.
267 *
268 * @throws NullPointerException if any of {@code elements} is null
269 * @since 3.0
270 */
271 public static <E> ImmutableList<E> copyOf(E[] elements) {
272 switch (elements.length) {
273 case 0:
274 return ImmutableList.of();
275 case 1:
276 return new SingletonImmutableList<E>(elements[0]);
277 default:
278 return construct(elements.clone());
279 }
280 }
281
282 private static <E> ImmutableList<E> copyFromCollection(
283 Collection<? extends E> collection) {
284 Object[] elements = collection.toArray();
285 switch (elements.length) {
286 case 0:
287 return of();
288 case 1:
289 @SuppressWarnings("unchecked") // collection had only Es in it
290 ImmutableList<E> list = new SingletonImmutableList<E>((E) elements[0]);
291 return list;
292 default:
293 // safe to use the array without copying it
294 // as specified by Collection.toArray().
295 return construct(elements);
296 }
297 }
298
299 /** {@code elements} has to be internally created array. */
300 private static <E> ImmutableList<E> construct(Object... elements) {
301 for (int i = 0; i < elements.length; i++) {
302 checkElementNotNull(elements[i], i);
303 }
304 return new RegularImmutableList<E>(elements);
305 }
306
307 // We do this instead of Preconditions.checkNotNull to save boxing and array
308 // creation cost.
309 private static Object checkElementNotNull(Object element, int index) {
310 if (element == null) {
311 throw new NullPointerException("at index " + index);
312 }
313 return element;
314 }
315
316 ImmutableList() {}
317
318 // This declaration is needed to make List.iterator() and
319 // ImmutableCollection.iterator() consistent.
320 @Override public UnmodifiableIterator<E> iterator() {
321 return listIterator();
322 }
323
324 @Override public UnmodifiableListIterator<E> listIterator() {
325 return listIterator(0);
326 }
327
328 @Override public UnmodifiableListIterator<E> listIterator(int index) {
329 return new AbstractIndexedListIterator<E>(size(), index) {
330 @Override
331 protected E get(int index) {
332 return ImmutableList.this.get(index);
333 }
334 };
335 }
336
337 @Override
338 public int indexOf(@Nullable Object object) {
339 return (object == null) ? -1 : Lists.indexOfImpl(this, object);
340 }
341
342 @Override
343 public int lastIndexOf(@Nullable Object object) {
344 return (object == null) ? -1 : Lists.lastIndexOfImpl(this, object);
345 }
346
347 @Override
348 public boolean contains(@Nullable Object object) {
349 return indexOf(object) >= 0;
350 }
351
352 // constrain the return type to ImmutableList<E>
353
354 /**
355 * Returns an immutable list of the elements between the specified {@code
356 * fromIndex}, inclusive, and {@code toIndex}, exclusive. (If {@code
357 * fromIndex} and {@code toIndex} are equal, the empty immutable list is
358 * returned.)
359 */
360 @Override
361 public ImmutableList<E> subList(int fromIndex, int toIndex) {
362 checkPositionIndexes(fromIndex, toIndex, size());
363 int length = toIndex - fromIndex;
364 switch (length) {
365 case 0:
366 return of();
367 case 1:
368 return of(get(fromIndex));
369 default:
370 return subListUnchecked(fromIndex, toIndex);
371 }
372 }
373
374 /**
375 * Called by the default implementation of {@link #subList} when
376 * {@code toIndex - fromIndex > 1}, after index validation has already been performed.
377 */
378 ImmutableList<E> subListUnchecked(int fromIndex, int toIndex) {
379 return new SubList(fromIndex, toIndex - fromIndex);
380 }
381
382 class SubList extends ImmutableList<E> {
383 transient final int offset;
384 transient final int length;
385
386 SubList(int offset, int length) {
387 this.offset = offset;
388 this.length = length;
389 }
390
391 @Override
392 public int size() {
393 return length;
394 }
395
396 @Override
397 public E get(int index) {
398 checkElementIndex(index, length);
399 return ImmutableList.this.get(index + offset);
400 }
401
402 @Override
403 public ImmutableList<E> subList(int fromIndex, int toIndex) {
404 checkPositionIndexes(fromIndex, toIndex, length);
405 return ImmutableList.this.subList(fromIndex + offset, toIndex + offset);
406 }
407
408 @Override
409 boolean isPartialView() {
410 return true;
411 }
412 }
413
414 /**
415 * Guaranteed to throw an exception and leave the list unmodified.
416 *
417 * @throws UnsupportedOperationException always
418 */
419 @Override
420 public final boolean addAll(int index, Collection<? extends E> newElements) {
421 throw new UnsupportedOperationException();
422 }
423
424 /**
425 * Guaranteed to throw an exception and leave the list unmodified.
426 *
427 * @throws UnsupportedOperationException always
428 */
429 @Override
430 public final E set(int index, E element) {
431 throw new UnsupportedOperationException();
432 }
433
434 /**
435 * Guaranteed to throw an exception and leave the list unmodified.
436 *
437 * @throws UnsupportedOperationException always
438 */
439 @Override
440 public final void add(int index, E element) {
441 throw new UnsupportedOperationException();
442 }
443
444 /**
445 * Guaranteed to throw an exception and leave the list unmodified.
446 *
447 * @throws UnsupportedOperationException always
448 */
449 @Override
450 public final E remove(int index) {
451 throw new UnsupportedOperationException();
452 }
453
454 /**
455 * Returns this list instance.
456 *
457 * @since 2.0
458 */
459 @Override public ImmutableList<E> asList() {
460 return this;
461 }
462
463 /**
464 * Returns a view of this immutable list in reverse order. For example, {@code
465 * ImmutableList.of(1, 2, 3).reverse()} is equivalent to {@code
466 * ImmutableList.of(3, 2, 1)}.
467 *
468 * @return a view of this immutable list in reverse order
469 * @since 7.0
470 */
471 public ImmutableList<E> reverse() {
472 return new ReverseImmutableList<E>(this);
473 }
474
475 private static class ReverseImmutableList<E> extends ImmutableList<E> {
476 private final transient ImmutableList<E> forwardList;
477 private final transient int size;
478
479 ReverseImmutableList(ImmutableList<E> backingList) {
480 this.forwardList = backingList;
481 this.size = backingList.size();
482 }
483
484 private int reverseIndex(int index) {
485 return (size - 1) - index;
486 }
487
488 private int reversePosition(int index) {
489 return size - index;
490 }
491
492 @Override public ImmutableList<E> reverse() {
493 return forwardList;
494 }
495
496 @Override public boolean contains(@Nullable Object object) {
497 return forwardList.contains(object);
498 }
499
500 @Override public boolean containsAll(Collection<?> targets) {
501 return forwardList.containsAll(targets);
502 }
503
504 @Override public int indexOf(@Nullable Object object) {
505 int index = forwardList.lastIndexOf(object);
506 return (index >= 0) ? reverseIndex(index) : -1;
507 }
508
509 @Override public int lastIndexOf(@Nullable Object object) {
510 int index = forwardList.indexOf(object);
511 return (index >= 0) ? reverseIndex(index) : -1;
512 }
513
514 @Override public ImmutableList<E> subList(int fromIndex, int toIndex) {
515 checkPositionIndexes(fromIndex, toIndex, size);
516 return forwardList.subList(
517 reversePosition(toIndex), reversePosition(fromIndex)).reverse();
518 }
519
520 @Override public E get(int index) {
521 checkElementIndex(index, size);
522 return forwardList.get(reverseIndex(index));
523 }
524
525 @Override public UnmodifiableListIterator<E> listIterator(int index) {
526 checkPositionIndex(index, size);
527 final UnmodifiableListIterator<E> forward =
528 forwardList.listIterator(reversePosition(index));
529 return new UnmodifiableListIterator<E>() {
530 @Override public boolean hasNext() {
531 return forward.hasPrevious();
532 }
533
534 @Override public boolean hasPrevious() {
535 return forward.hasNext();
536 }
537
538 @Override public E next() {
539 return forward.previous();
540 }
541
542 @Override public int nextIndex() {
543 return reverseIndex(forward.previousIndex());
544 }
545
546 @Override public E previous() {
547 return forward.next();
548 }
549
550 @Override public int previousIndex() {
551 return reverseIndex(forward.nextIndex());
552 }
553 };
554 }
555
556 @Override public int size() {
557 return size;
558 }
559
560 @Override public boolean isEmpty() {
561 return forwardList.isEmpty();
562 }
563
564 @Override boolean isPartialView() {
565 return forwardList.isPartialView();
566 }
567 }
568
569 @Override public boolean equals(Object obj) {
570 return Lists.equalsImpl(this, obj);
571 }
572
573 @Override public int hashCode() {
574 return Lists.hashCodeImpl(this);
575 }
576
577 /*
578 * Serializes ImmutableLists as their logical contents. This ensures that
579 * implementation types do not leak into the serialized representation.
580 */
581 private static class SerializedForm implements Serializable {
582 final Object[] elements;
583 SerializedForm(Object[] elements) {
584 this.elements = elements;
585 }
586 Object readResolve() {
587 return copyOf(elements);
588 }
589 private static final long serialVersionUID = 0;
590 }
591
592 private void readObject(ObjectInputStream stream)
593 throws InvalidObjectException {
594 throw new InvalidObjectException("Use SerializedForm");
595 }
596
597 @Override Object writeReplace() {
598 return new SerializedForm(toArray());
599 }
600
601 /**
602 * Returns a new builder. The generated builder is equivalent to the builder
603 * created by the {@link Builder} constructor.
604 */
605 public static <E> Builder<E> builder() {
606 return new Builder<E>();
607 }
608
609 /**
610 * A builder for creating immutable list instances, especially {@code public
611 * static final} lists ("constant lists"). Example: <pre> {@code
612 *
613 * public static final ImmutableList<Color> GOOGLE_COLORS
614 * = new ImmutableList.Builder<Color>()
615 * .addAll(WEBSAFE_COLORS)
616 * .add(new Color(0, 191, 255))
617 * .build();}</pre>
618 *
619 * Builder instances can be reused; it is safe to call {@link #build} multiple
620 * times to build multiple lists in series. Each new list contains all the
621 * elements of the ones created before it.
622 *
623 * @since 2.0 (imported from Google Collections Library)
624 */
625 public static final class Builder<E> extends ImmutableCollection.Builder<E> {
626 private final ArrayList<E> contents = Lists.newArrayList();
627
628 /**
629 * Creates a new builder. The returned builder is equivalent to the builder
630 * generated by {@link ImmutableList#builder}.
631 */
632 public Builder() {}
633
634 /**
635 * Adds {@code element} to the {@code ImmutableList}.
636 *
637 * @param element the element to add
638 * @return this {@code Builder} object
639 * @throws NullPointerException if {@code element} is null
640 */
641 @Override public Builder<E> add(E element) {
642 contents.add(checkNotNull(element));
643 return this;
644 }
645
646 /**
647 * Adds each element of {@code elements} to the {@code ImmutableList}.
648 *
649 * @param elements the {@code Iterable} to add to the {@code ImmutableList}
650 * @return this {@code Builder} object
651 * @throws NullPointerException if {@code elements} is null or contains a
652 * null element
653 */
654 @Override public Builder<E> addAll(Iterable<? extends E> elements) {
655 if (elements instanceof Collection) {
656 Collection<?> collection = (Collection<?>) elements;
657 contents.ensureCapacity(contents.size() + collection.size());
658 }
659 super.addAll(elements);
660 return this;
661 }
662
663 /**
664 * Adds each element of {@code elements} to the {@code ImmutableList}.
665 *
666 * @param elements the {@code Iterable} to add to the {@code ImmutableList}
667 * @return this {@code Builder} object
668 * @throws NullPointerException if {@code elements} is null or contains a
669 * null element
670 */
671 @Override public Builder<E> add(E... elements) {
672 contents.ensureCapacity(contents.size() + elements.length);
673 super.add(elements);
674 return this;
675 }
676
677 /**
678 * Adds each element of {@code elements} to the {@code ImmutableList}.
679 *
680 * @param elements the {@code Iterable} to add to the {@code ImmutableList}
681 * @return this {@code Builder} object
682 * @throws NullPointerException if {@code elements} is null or contains a
683 * null element
684 */
685 @Override public Builder<E> addAll(Iterator<? extends E> elements) {
686 super.addAll(elements);
687 return this;
688 }
689
690 /**
691 * Returns a newly-created {@code ImmutableList} based on the contents of
692 * the {@code Builder}.
693 */
694 @Override public ImmutableList<E> build() {
695 return copyOf(contents);
696 }
697 }
698 }