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.checkArgument;
020 import static com.google.common.base.Preconditions.checkNotNull;
021
022 import com.google.common.annotations.Beta;
023 import com.google.common.annotations.GwtCompatible;
024 import com.google.common.annotations.GwtIncompatible;
025 import com.google.common.base.Function;
026 import com.google.common.base.Optional;
027 import com.google.common.base.Preconditions;
028 import com.google.common.base.Predicate;
029
030 import java.util.Arrays;
031 import java.util.Collection;
032 import java.util.Collections;
033 import java.util.Comparator;
034 import java.util.Iterator;
035 import java.util.List;
036 import java.util.NoSuchElementException;
037 import java.util.Queue;
038 import java.util.RandomAccess;
039 import java.util.Set;
040 import java.util.SortedSet;
041
042 import javax.annotation.Nullable;
043
044 /**
045 * This class contains static utility methods that operate on or return objects
046 * of type {@code Iterable}. Except as noted, each method has a corresponding
047 * {@link Iterator}-based method in the {@link Iterators} class.
048 *
049 * <p><i>Performance notes:</i> Unless otherwise noted, all of the iterables
050 * produced in this class are <i>lazy</i>, which means that their iterators
051 * only advance the backing iteration when absolutely necessary.
052 *
053 * <p>See the Guava User Guide article on <a href=
054 * "http://code.google.com/p/guava-libraries/wiki/CollectionUtilitiesExplained#Iterables">
055 * {@code Iterables}</a>.
056 *
057 * @author Kevin Bourrillion
058 * @author Jared Levy
059 * @since 2.0 (imported from Google Collections Library)
060 */
061 @GwtCompatible(emulated = true)
062 public final class Iterables {
063 private Iterables() {}
064
065 /** Returns an unmodifiable view of {@code iterable}. */
066 public static <T> Iterable<T> unmodifiableIterable(
067 final Iterable<T> iterable) {
068 checkNotNull(iterable);
069 if (iterable instanceof UnmodifiableIterable ||
070 iterable instanceof ImmutableCollection) {
071 return iterable;
072 }
073 return new UnmodifiableIterable<T>(iterable);
074 }
075
076 /**
077 * Simply returns its argument.
078 *
079 * @deprecated no need to use this
080 * @since 10.0
081 */
082 @Deprecated public static <E> Iterable<E> unmodifiableIterable(
083 ImmutableCollection<E> iterable) {
084 return checkNotNull(iterable);
085 }
086
087 private static final class UnmodifiableIterable<T> extends FluentIterable<T> {
088 private final Iterable<T> iterable;
089
090 private UnmodifiableIterable(Iterable<T> iterable) {
091 this.iterable = iterable;
092 }
093
094 @Override
095 public Iterator<T> iterator() {
096 return Iterators.unmodifiableIterator(iterable.iterator());
097 }
098
099 @Override
100 public String toString() {
101 return iterable.toString();
102 }
103 // no equals and hashCode; it would break the contract!
104 }
105
106 /**
107 * Returns the number of elements in {@code iterable}.
108 */
109 public static int size(Iterable<?> iterable) {
110 return (iterable instanceof Collection)
111 ? ((Collection<?>) iterable).size()
112 : Iterators.size(iterable.iterator());
113 }
114
115 /**
116 * Returns {@code true} if {@code iterable} contains any object for which {@code equals(element)}
117 * is true.
118 */
119 public static boolean contains(Iterable<?> iterable, @Nullable Object element)
120 {
121 if (iterable instanceof Collection) {
122 Collection<?> collection = (Collection<?>) iterable;
123 try {
124 return collection.contains(element);
125 } catch (NullPointerException e) {
126 return false;
127 } catch (ClassCastException e) {
128 return false;
129 }
130 }
131 return Iterators.contains(iterable.iterator(), element);
132 }
133
134 /**
135 * Removes, from an iterable, every element that belongs to the provided
136 * collection.
137 *
138 * <p>This method calls {@link Collection#removeAll} if {@code iterable} is a
139 * collection, and {@link Iterators#removeAll} otherwise.
140 *
141 * @param removeFrom the iterable to (potentially) remove elements from
142 * @param elementsToRemove the elements to remove
143 * @return {@code true} if any element was removed from {@code iterable}
144 */
145 public static boolean removeAll(
146 Iterable<?> removeFrom, Collection<?> elementsToRemove) {
147 return (removeFrom instanceof Collection)
148 ? ((Collection<?>) removeFrom).removeAll(checkNotNull(elementsToRemove))
149 : Iterators.removeAll(removeFrom.iterator(), elementsToRemove);
150 }
151
152 /**
153 * Removes, from an iterable, every element that does not belong to the
154 * provided collection.
155 *
156 * <p>This method calls {@link Collection#retainAll} if {@code iterable} is a
157 * collection, and {@link Iterators#retainAll} otherwise.
158 *
159 * @param removeFrom the iterable to (potentially) remove elements from
160 * @param elementsToRetain the elements to retain
161 * @return {@code true} if any element was removed from {@code iterable}
162 */
163 public static boolean retainAll(
164 Iterable<?> removeFrom, Collection<?> elementsToRetain) {
165 return (removeFrom instanceof Collection)
166 ? ((Collection<?>) removeFrom).retainAll(checkNotNull(elementsToRetain))
167 : Iterators.retainAll(removeFrom.iterator(), elementsToRetain);
168 }
169
170 /**
171 * Removes, from an iterable, every element that satisfies the provided
172 * predicate.
173 *
174 * @param removeFrom the iterable to (potentially) remove elements from
175 * @param predicate a predicate that determines whether an element should
176 * be removed
177 * @return {@code true} if any elements were removed from the iterable
178 *
179 * @throws UnsupportedOperationException if the iterable does not support
180 * {@code remove()}.
181 * @since 2.0
182 */
183 public static <T> boolean removeIf(
184 Iterable<T> removeFrom, Predicate<? super T> predicate) {
185 if (removeFrom instanceof RandomAccess && removeFrom instanceof List) {
186 return removeIfFromRandomAccessList(
187 (List<T>) removeFrom, checkNotNull(predicate));
188 }
189 return Iterators.removeIf(removeFrom.iterator(), predicate);
190 }
191
192 private static <T> boolean removeIfFromRandomAccessList(
193 List<T> list, Predicate<? super T> predicate) {
194 // Note: Not all random access lists support set() so we need to deal with
195 // those that don't and attempt the slower remove() based solution.
196 int from = 0;
197 int to = 0;
198
199 for (; from < list.size(); from++) {
200 T element = list.get(from);
201 if (!predicate.apply(element)) {
202 if (from > to) {
203 try {
204 list.set(to, element);
205 } catch (UnsupportedOperationException e) {
206 slowRemoveIfForRemainingElements(list, predicate, to, from);
207 return true;
208 }
209 }
210 to++;
211 }
212 }
213
214 // Clear the tail of any remaining items
215 list.subList(to, list.size()).clear();
216 return from != to;
217 }
218
219 private static <T> void slowRemoveIfForRemainingElements(List<T> list,
220 Predicate<? super T> predicate, int to, int from) {
221 // Here we know that:
222 // * (to < from) and that both are valid indices.
223 // * Everything with (index < to) should be kept.
224 // * Everything with (to <= index < from) should be removed.
225 // * The element with (index == from) should be kept.
226 // * Everything with (index > from) has not been checked yet.
227
228 // Check from the end of the list backwards (minimize expected cost of
229 // moving elements when remove() is called). Stop before 'from' because
230 // we already know that should be kept.
231 for (int n = list.size() - 1; n > from; n--) {
232 if (predicate.apply(list.get(n))) {
233 list.remove(n);
234 }
235 }
236 // And now remove everything in the range [to, from) (going backwards).
237 for (int n = from - 1; n >= to; n--) {
238 list.remove(n);
239 }
240 }
241
242 /**
243 * Determines whether two iterables contain equal elements in the same order.
244 * More specifically, this method returns {@code true} if {@code iterable1}
245 * and {@code iterable2} contain the same number of elements and every element
246 * of {@code iterable1} is equal to the corresponding element of
247 * {@code iterable2}.
248 */
249 public static boolean elementsEqual(
250 Iterable<?> iterable1, Iterable<?> iterable2) {
251 return Iterators.elementsEqual(iterable1.iterator(), iterable2.iterator());
252 }
253
254 /**
255 * Returns a string representation of {@code iterable}, with the format
256 * {@code [e1, e2, ..., en]}.
257 */
258 public static String toString(Iterable<?> iterable) {
259 return Iterators.toString(iterable.iterator());
260 }
261
262 /**
263 * Returns the single element contained in {@code iterable}.
264 *
265 * @throws NoSuchElementException if the iterable is empty
266 * @throws IllegalArgumentException if the iterable contains multiple
267 * elements
268 */
269 public static <T> T getOnlyElement(Iterable<T> iterable) {
270 return Iterators.getOnlyElement(iterable.iterator());
271 }
272
273 /**
274 * Returns the single element contained in {@code iterable}, or {@code
275 * defaultValue} if the iterable is empty.
276 *
277 * @throws IllegalArgumentException if the iterator contains multiple
278 * elements
279 */
280 public static <T> T getOnlyElement(
281 Iterable<? extends T> iterable, @Nullable T defaultValue) {
282 return Iterators.getOnlyElement(iterable.iterator(), defaultValue);
283 }
284
285 /**
286 * Copies an iterable's elements into an array.
287 *
288 * @param iterable the iterable to copy
289 * @param type the type of the elements
290 * @return a newly-allocated array into which all the elements of the iterable
291 * have been copied
292 */
293 @GwtIncompatible("Array.newInstance(Class, int)")
294 public static <T> T[] toArray(Iterable<? extends T> iterable, Class<T> type) {
295 Collection<? extends T> collection = toCollection(iterable);
296 T[] array = ObjectArrays.newArray(type, collection.size());
297 return collection.toArray(array);
298 }
299
300 /**
301 * Copies an iterable's elements into an array.
302 *
303 * @param iterable the iterable to copy
304 * @return a newly-allocated array into which all the elements of the iterable
305 * have been copied
306 */
307 static Object[] toArray(Iterable<?> iterable) {
308 return toCollection(iterable).toArray();
309 }
310
311 /**
312 * Converts an iterable into a collection. If the iterable is already a
313 * collection, it is returned. Otherwise, an {@link java.util.ArrayList} is
314 * created with the contents of the iterable in the same iteration order.
315 */
316 private static <E> Collection<E> toCollection(Iterable<E> iterable) {
317 return (iterable instanceof Collection)
318 ? (Collection<E>) iterable
319 : Lists.newArrayList(iterable.iterator());
320 }
321
322 /**
323 * Adds all elements in {@code iterable} to {@code collection}.
324 *
325 * @return {@code true} if {@code collection} was modified as a result of this
326 * operation.
327 */
328 public static <T> boolean addAll(
329 Collection<T> addTo, Iterable<? extends T> elementsToAdd) {
330 if (elementsToAdd instanceof Collection) {
331 Collection<? extends T> c = Collections2.cast(elementsToAdd);
332 return addTo.addAll(c);
333 }
334 return Iterators.addAll(addTo, elementsToAdd.iterator());
335 }
336
337 /**
338 * Returns the number of elements in the specified iterable that equal the
339 * specified object. This implementation avoids a full iteration when the
340 * iterable is a {@link Multiset} or {@link Set}.
341 *
342 * @see Collections#frequency
343 */
344 public static int frequency(Iterable<?> iterable, @Nullable Object element) {
345 if ((iterable instanceof Multiset)) {
346 return ((Multiset<?>) iterable).count(element);
347 }
348 if ((iterable instanceof Set)) {
349 return ((Set<?>) iterable).contains(element) ? 1 : 0;
350 }
351 return Iterators.frequency(iterable.iterator(), element);
352 }
353
354 /**
355 * Returns an iterable whose iterators cycle indefinitely over the elements of
356 * {@code iterable}.
357 *
358 * <p>That iterator supports {@code remove()} if {@code iterable.iterator()}
359 * does. After {@code remove()} is called, subsequent cycles omit the removed
360 * element, which is no longer in {@code iterable}. The iterator's
361 * {@code hasNext()} method returns {@code true} until {@code iterable} is
362 * empty.
363 *
364 * <p><b>Warning:</b> Typical uses of the resulting iterator may produce an
365 * infinite loop. You should use an explicit {@code break} or be certain that
366 * you will eventually remove all the elements.
367 *
368 * <p>To cycle over the iterable {@code n} times, use the following:
369 * {@code Iterables.concat(Collections.nCopies(n, iterable))}
370 */
371 public static <T> Iterable<T> cycle(final Iterable<T> iterable) {
372 checkNotNull(iterable);
373 return new FluentIterable<T>() {
374 @Override
375 public Iterator<T> iterator() {
376 return Iterators.cycle(iterable);
377 }
378 @Override public String toString() {
379 return iterable.toString() + " (cycled)";
380 }
381 };
382 }
383
384 /**
385 * Returns an iterable whose iterators cycle indefinitely over the provided
386 * elements.
387 *
388 * <p>After {@code remove} is invoked on a generated iterator, the removed
389 * element will no longer appear in either that iterator or any other iterator
390 * created from the same source iterable. That is, this method behaves exactly
391 * as {@code Iterables.cycle(Lists.newArrayList(elements))}. The iterator's
392 * {@code hasNext} method returns {@code true} until all of the original
393 * elements have been removed.
394 *
395 * <p><b>Warning:</b> Typical uses of the resulting iterator may produce an
396 * infinite loop. You should use an explicit {@code break} or be certain that
397 * you will eventually remove all the elements.
398 *
399 * <p>To cycle over the elements {@code n} times, use the following:
400 * {@code Iterables.concat(Collections.nCopies(n, Arrays.asList(elements)))}
401 */
402 public static <T> Iterable<T> cycle(T... elements) {
403 return cycle(Lists.newArrayList(elements));
404 }
405
406 /**
407 * Combines two iterables into a single iterable. The returned iterable has an
408 * iterator that traverses the elements in {@code a}, followed by the elements
409 * in {@code b}. The source iterators are not polled until necessary.
410 *
411 * <p>The returned iterable's iterator supports {@code remove()} when the
412 * corresponding input iterator supports it.
413 */
414 @SuppressWarnings("unchecked")
415 public static <T> Iterable<T> concat(
416 Iterable<? extends T> a, Iterable<? extends T> b) {
417 checkNotNull(a);
418 checkNotNull(b);
419 return concat(Arrays.asList(a, b));
420 }
421
422 /**
423 * Combines three iterables into a single iterable. The returned iterable has
424 * an iterator that traverses the elements in {@code a}, followed by the
425 * elements in {@code b}, followed by the elements in {@code c}. The source
426 * iterators are not polled until necessary.
427 *
428 * <p>The returned iterable's iterator supports {@code remove()} when the
429 * corresponding input iterator supports it.
430 */
431 @SuppressWarnings("unchecked")
432 public static <T> Iterable<T> concat(Iterable<? extends T> a,
433 Iterable<? extends T> b, Iterable<? extends T> c) {
434 checkNotNull(a);
435 checkNotNull(b);
436 checkNotNull(c);
437 return concat(Arrays.asList(a, b, c));
438 }
439
440 /**
441 * Combines four iterables into a single iterable. The returned iterable has
442 * an iterator that traverses the elements in {@code a}, followed by the
443 * elements in {@code b}, followed by the elements in {@code c}, followed by
444 * the elements in {@code d}. The source iterators are not polled until
445 * necessary.
446 *
447 * <p>The returned iterable's iterator supports {@code remove()} when the
448 * corresponding input iterator supports it.
449 */
450 @SuppressWarnings("unchecked")
451 public static <T> Iterable<T> concat(Iterable<? extends T> a,
452 Iterable<? extends T> b, Iterable<? extends T> c,
453 Iterable<? extends T> d) {
454 checkNotNull(a);
455 checkNotNull(b);
456 checkNotNull(c);
457 checkNotNull(d);
458 return concat(Arrays.asList(a, b, c, d));
459 }
460
461 /**
462 * Combines multiple iterables into a single iterable. The returned iterable
463 * has an iterator that traverses the elements of each iterable in
464 * {@code inputs}. The input iterators are not polled until necessary.
465 *
466 * <p>The returned iterable's iterator supports {@code remove()} when the
467 * corresponding input iterator supports it.
468 *
469 * @throws NullPointerException if any of the provided iterables is null
470 */
471 public static <T> Iterable<T> concat(Iterable<? extends T>... inputs) {
472 return concat(ImmutableList.copyOf(inputs));
473 }
474
475 /**
476 * Combines multiple iterables into a single iterable. The returned iterable
477 * has an iterator that traverses the elements of each iterable in
478 * {@code inputs}. The input iterators are not polled until necessary.
479 *
480 * <p>The returned iterable's iterator supports {@code remove()} when the
481 * corresponding input iterator supports it. The methods of the returned
482 * iterable may throw {@code NullPointerException} if any of the input
483 * iterators is null.
484 */
485 public static <T> Iterable<T> concat(
486 final Iterable<? extends Iterable<? extends T>> inputs) {
487 checkNotNull(inputs);
488 return new FluentIterable<T>() {
489 @Override
490 public Iterator<T> iterator() {
491 return Iterators.concat(iterators(inputs));
492 }
493 };
494 }
495
496 /**
497 * Returns an iterator over the iterators of the given iterables.
498 */
499 private static <T> UnmodifiableIterator<Iterator<? extends T>> iterators(
500 Iterable<? extends Iterable<? extends T>> iterables) {
501 final Iterator<? extends Iterable<? extends T>> iterableIterator =
502 iterables.iterator();
503 return new UnmodifiableIterator<Iterator<? extends T>>() {
504 @Override
505 public boolean hasNext() {
506 return iterableIterator.hasNext();
507 }
508 @Override
509 public Iterator<? extends T> next() {
510 return iterableIterator.next().iterator();
511 }
512 };
513 }
514
515 /**
516 * Divides an iterable into unmodifiable sublists of the given size (the final
517 * iterable may be smaller). For example, partitioning an iterable containing
518 * {@code [a, b, c, d, e]} with a partition size of 3 yields {@code
519 * [[a, b, c], [d, e]]} -- an outer iterable containing two inner lists of
520 * three and two elements, all in the original order.
521 *
522 * <p>Iterators returned by the returned iterable do not support the {@link
523 * Iterator#remove()} method. The returned lists implement {@link
524 * RandomAccess}, whether or not the input list does.
525 *
526 * <p><b>Note:</b> if {@code iterable} is a {@link List}, use {@link
527 * Lists#partition(List, int)} instead.
528 *
529 * @param iterable the iterable to return a partitioned view of
530 * @param size the desired size of each partition (the last may be smaller)
531 * @return an iterable of unmodifiable lists containing the elements of {@code
532 * iterable} divided into partitions
533 * @throws IllegalArgumentException if {@code size} is nonpositive
534 */
535 public static <T> Iterable<List<T>> partition(
536 final Iterable<T> iterable, final int size) {
537 checkNotNull(iterable);
538 checkArgument(size > 0);
539 return new FluentIterable<List<T>>() {
540 @Override
541 public Iterator<List<T>> iterator() {
542 return Iterators.partition(iterable.iterator(), size);
543 }
544 };
545 }
546
547 /**
548 * Divides an iterable into unmodifiable sublists of the given size, padding
549 * the final iterable with null values if necessary. For example, partitioning
550 * an iterable containing {@code [a, b, c, d, e]} with a partition size of 3
551 * yields {@code [[a, b, c], [d, e, null]]} -- an outer iterable containing
552 * two inner lists of three elements each, all in the original order.
553 *
554 * <p>Iterators returned by the returned iterable do not support the {@link
555 * Iterator#remove()} method.
556 *
557 * @param iterable the iterable to return a partitioned view of
558 * @param size the desired size of each partition
559 * @return an iterable of unmodifiable lists containing the elements of {@code
560 * iterable} divided into partitions (the final iterable may have
561 * trailing null elements)
562 * @throws IllegalArgumentException if {@code size} is nonpositive
563 */
564 public static <T> Iterable<List<T>> paddedPartition(
565 final Iterable<T> iterable, final int size) {
566 checkNotNull(iterable);
567 checkArgument(size > 0);
568 return new FluentIterable<List<T>>() {
569 @Override
570 public Iterator<List<T>> iterator() {
571 return Iterators.paddedPartition(iterable.iterator(), size);
572 }
573 };
574 }
575
576 /**
577 * Returns the elements of {@code unfiltered} that satisfy a predicate. The
578 * resulting iterable's iterator does not support {@code remove()}.
579 */
580 public static <T> Iterable<T> filter(
581 final Iterable<T> unfiltered, final Predicate<? super T> predicate) {
582 checkNotNull(unfiltered);
583 checkNotNull(predicate);
584 return new FluentIterable<T>() {
585 @Override
586 public Iterator<T> iterator() {
587 return Iterators.filter(unfiltered.iterator(), predicate);
588 }
589 };
590 }
591
592 /**
593 * Returns all instances of class {@code type} in {@code unfiltered}. The
594 * returned iterable has elements whose class is {@code type} or a subclass of
595 * {@code type}. The returned iterable's iterator does not support
596 * {@code remove()}.
597 *
598 * @param unfiltered an iterable containing objects of any type
599 * @param type the type of elements desired
600 * @return an unmodifiable iterable containing all elements of the original
601 * iterable that were of the requested type
602 */
603 @GwtIncompatible("Class.isInstance")
604 public static <T> Iterable<T> filter(
605 final Iterable<?> unfiltered, final Class<T> type) {
606 checkNotNull(unfiltered);
607 checkNotNull(type);
608 return new FluentIterable<T>() {
609 @Override
610 public Iterator<T> iterator() {
611 return Iterators.filter(unfiltered.iterator(), type);
612 }
613 };
614 }
615
616 /**
617 * Returns {@code true} if any element in {@code iterable} satisfies the predicate.
618 */
619 public static <T> boolean any(
620 Iterable<T> iterable, Predicate<? super T> predicate) {
621 return Iterators.any(iterable.iterator(), predicate);
622 }
623
624 /**
625 * Returns {@code true} if every element in {@code iterable} satisfies the
626 * predicate. If {@code iterable} is empty, {@code true} is returned.
627 */
628 public static <T> boolean all(
629 Iterable<T> iterable, Predicate<? super T> predicate) {
630 return Iterators.all(iterable.iterator(), predicate);
631 }
632
633 /**
634 * Returns the first element in {@code iterable} that satisfies the given
635 * predicate; use this method only when such an element is known to exist. If
636 * it is possible that <i>no</i> element will match, use {@link #tryFind} or
637 * {@link #find(Iterable, Predicate, Object)} instead.
638 *
639 * @throws NoSuchElementException if no element in {@code iterable} matches
640 * the given predicate
641 */
642 public static <T> T find(Iterable<T> iterable,
643 Predicate<? super T> predicate) {
644 return Iterators.find(iterable.iterator(), predicate);
645 }
646
647 /**
648 * Returns the first element in {@code iterable} that satisfies the given
649 * predicate, or {@code defaultValue} if none found. Note that this can
650 * usually be handled more naturally using {@code
651 * tryFind(iterable, predicate).or(defaultValue)}.
652 *
653 * @since 7.0
654 */
655 public static <T> T find(Iterable<? extends T> iterable,
656 Predicate<? super T> predicate, @Nullable T defaultValue) {
657 return Iterators.find(iterable.iterator(), predicate, defaultValue);
658 }
659
660 /**
661 * Returns an {@link Optional} containing the first element in {@code
662 * iterable} that satisfies the given predicate, if such an element exists.
663 *
664 * <p><b>Warning:</b> avoid using a {@code predicate} that matches {@code
665 * null}. If {@code null} is matched in {@code iterable}, a
666 * NullPointerException will be thrown.
667 *
668 * @since 11.0
669 */
670 public static <T> Optional<T> tryFind(Iterable<T> iterable,
671 Predicate<? super T> predicate) {
672 return Iterators.tryFind(iterable.iterator(), predicate);
673 }
674
675 /**
676 * Returns the index in {@code iterable} of the first element that satisfies
677 * the provided {@code predicate}, or {@code -1} if the Iterable has no such
678 * elements.
679 *
680 * <p>More formally, returns the lowest index {@code i} such that
681 * {@code predicate.apply(Iterables.get(iterable, i))} returns {@code true},
682 * or {@code -1} if there is no such index.
683 *
684 * @since 2.0
685 */
686 public static <T> int indexOf(
687 Iterable<T> iterable, Predicate<? super T> predicate) {
688 return Iterators.indexOf(iterable.iterator(), predicate);
689 }
690
691 /**
692 * Returns an iterable that applies {@code function} to each element of {@code
693 * fromIterable}.
694 *
695 * <p>The returned iterable's iterator supports {@code remove()} if the
696 * provided iterator does. After a successful {@code remove()} call,
697 * {@code fromIterable} no longer contains the corresponding element.
698 *
699 * <p>If the input {@code Iterable} is known to be a {@code List} or other
700 * {@code Collection}, consider {@link Lists#transform} and {@link
701 * Collections2#transform}.
702 */
703 public static <F, T> Iterable<T> transform(final Iterable<F> fromIterable,
704 final Function<? super F, ? extends T> function) {
705 checkNotNull(fromIterable);
706 checkNotNull(function);
707 return new FluentIterable<T>() {
708 @Override
709 public Iterator<T> iterator() {
710 return Iterators.transform(fromIterable.iterator(), function);
711 }
712 };
713 }
714
715 /**
716 * Returns the element at the specified position in an iterable.
717 *
718 * @param position position of the element to return
719 * @return the element at the specified position in {@code iterable}
720 * @throws IndexOutOfBoundsException if {@code position} is negative or
721 * greater than or equal to the size of {@code iterable}
722 */
723 public static <T> T get(Iterable<T> iterable, int position) {
724 checkNotNull(iterable);
725 if (iterable instanceof List) {
726 return ((List<T>) iterable).get(position);
727 }
728
729 if (iterable instanceof Collection) {
730 // Can check both ends
731 Collection<T> collection = (Collection<T>) iterable;
732 Preconditions.checkElementIndex(position, collection.size());
733 } else {
734 // Can only check the lower end
735 checkNonnegativeIndex(position);
736 }
737 return Iterators.get(iterable.iterator(), position);
738 }
739
740 private static void checkNonnegativeIndex(int position) {
741 if (position < 0) {
742 throw new IndexOutOfBoundsException(
743 "position cannot be negative: " + position);
744 }
745 }
746
747 /**
748 * Returns the element at the specified position in an iterable or a default
749 * value otherwise.
750 *
751 * @param position position of the element to return
752 * @param defaultValue the default value to return if {@code position} is
753 * greater than or equal to the size of the iterable
754 * @return the element at the specified position in {@code iterable} or
755 * {@code defaultValue} if {@code iterable} contains fewer than
756 * {@code position + 1} elements.
757 * @throws IndexOutOfBoundsException if {@code position} is negative
758 * @since 4.0
759 */
760 public static <T> T get(Iterable<? extends T> iterable, int position, @Nullable T defaultValue) {
761 checkNotNull(iterable);
762 checkNonnegativeIndex(position);
763
764 try {
765 return get(iterable, position);
766 } catch (IndexOutOfBoundsException e) {
767 return defaultValue;
768 }
769 }
770
771 /**
772 * Returns the first element in {@code iterable} or {@code defaultValue} if
773 * the iterable is empty. The {@link Iterators} analog to this method is
774 * {@link Iterators#getNext}.
775 *
776 * @param defaultValue the default value to return if the iterable is empty
777 * @return the first element of {@code iterable} or the default value
778 * @since 7.0
779 */
780 public static <T> T getFirst(Iterable<? extends T> iterable, @Nullable T defaultValue) {
781 return Iterators.getNext(iterable.iterator(), defaultValue);
782 }
783
784 /**
785 * Returns the last element of {@code iterable}.
786 *
787 * @return the last element of {@code iterable}
788 * @throws NoSuchElementException if the iterable is empty
789 */
790 public static <T> T getLast(Iterable<T> iterable) {
791 // TODO(kevinb): Support a concurrently modified collection?
792 if (iterable instanceof List) {
793 List<T> list = (List<T>) iterable;
794 if (list.isEmpty()) {
795 throw new NoSuchElementException();
796 }
797 return getLastInNonemptyList(list);
798 }
799
800 /*
801 * TODO(kevinb): consider whether this "optimization" is worthwhile. Users
802 * with SortedSets tend to know they are SortedSets and probably would not
803 * call this method.
804 */
805 if (iterable instanceof SortedSet) {
806 SortedSet<T> sortedSet = (SortedSet<T>) iterable;
807 return sortedSet.last();
808 }
809
810 return Iterators.getLast(iterable.iterator());
811 }
812
813 /**
814 * Returns the last element of {@code iterable} or {@code defaultValue} if
815 * the iterable is empty.
816 *
817 * @param defaultValue the value to return if {@code iterable} is empty
818 * @return the last element of {@code iterable} or the default value
819 * @since 3.0
820 */
821 public static <T> T getLast(Iterable<? extends T> iterable, @Nullable T defaultValue) {
822 if (iterable instanceof Collection) {
823 Collection<? extends T> collection = Collections2.cast(iterable);
824 if (collection.isEmpty()) {
825 return defaultValue;
826 }
827 }
828
829 if (iterable instanceof List) {
830 List<? extends T> list = Lists.cast(iterable);
831 return getLastInNonemptyList(list);
832 }
833
834 /*
835 * TODO(kevinb): consider whether this "optimization" is worthwhile. Users
836 * with SortedSets tend to know they are SortedSets and probably would not
837 * call this method.
838 */
839 if (iterable instanceof SortedSet) {
840 SortedSet<? extends T> sortedSet = Sets.cast(iterable);
841 return sortedSet.last();
842 }
843
844 return Iterators.getLast(iterable.iterator(), defaultValue);
845 }
846
847 private static <T> T getLastInNonemptyList(List<T> list) {
848 return list.get(list.size() - 1);
849 }
850
851 /**
852 * Returns a view of {@code iterable} that skips its first
853 * {@code numberToSkip} elements. If {@code iterable} contains fewer than
854 * {@code numberToSkip} elements, the returned iterable skips all of its
855 * elements.
856 *
857 * <p>Modifications to the underlying {@link Iterable} before a call to
858 * {@code iterator()} are reflected in the returned iterator. That is, the
859 * iterator skips the first {@code numberToSkip} elements that exist when the
860 * {@code Iterator} is created, not when {@code skip()} is called.
861 *
862 * <p>The returned iterable's iterator supports {@code remove()} if the
863 * iterator of the underlying iterable supports it. Note that it is
864 * <i>not</i> possible to delete the last skipped element by immediately
865 * calling {@code remove()} on that iterator, as the {@code Iterator}
866 * contract states that a call to {@code remove()} before a call to
867 * {@code next()} will throw an {@link IllegalStateException}.
868 *
869 * @since 3.0
870 */
871 public static <T> Iterable<T> skip(final Iterable<T> iterable,
872 final int numberToSkip) {
873 checkNotNull(iterable);
874 checkArgument(numberToSkip >= 0, "number to skip cannot be negative");
875
876 if (iterable instanceof List) {
877 final List<T> list = (List<T>) iterable;
878 return new FluentIterable<T>() {
879 @Override
880 public Iterator<T> iterator() {
881 // TODO(kevinb): Support a concurrently modified collection?
882 return (numberToSkip >= list.size())
883 ? Iterators.<T>emptyIterator()
884 : list.subList(numberToSkip, list.size()).iterator();
885 }
886 };
887 }
888
889 return new FluentIterable<T>() {
890 @Override
891 public Iterator<T> iterator() {
892 final Iterator<T> iterator = iterable.iterator();
893
894 Iterators.advance(iterator, numberToSkip);
895
896 /*
897 * We can't just return the iterator because an immediate call to its
898 * remove() method would remove one of the skipped elements instead of
899 * throwing an IllegalStateException.
900 */
901 return new Iterator<T>() {
902 boolean atStart = true;
903
904 @Override
905 public boolean hasNext() {
906 return iterator.hasNext();
907 }
908
909 @Override
910 public T next() {
911 if (!hasNext()) {
912 throw new NoSuchElementException();
913 }
914
915 try {
916 return iterator.next();
917 } finally {
918 atStart = false;
919 }
920 }
921
922 @Override
923 public void remove() {
924 if (atStart) {
925 throw new IllegalStateException();
926 }
927 iterator.remove();
928 }
929 };
930 }
931 };
932 }
933
934 /**
935 * Creates an iterable with the first {@code limitSize} elements of the given
936 * iterable. If the original iterable does not contain that many elements, the
937 * returned iterator will have the same behavior as the original iterable. The
938 * returned iterable's iterator supports {@code remove()} if the original
939 * iterator does.
940 *
941 * @param iterable the iterable to limit
942 * @param limitSize the maximum number of elements in the returned iterator
943 * @throws IllegalArgumentException if {@code limitSize} is negative
944 * @since 3.0
945 */
946 public static <T> Iterable<T> limit(
947 final Iterable<T> iterable, final int limitSize) {
948 checkNotNull(iterable);
949 checkArgument(limitSize >= 0, "limit is negative");
950 return new FluentIterable<T>() {
951 @Override
952 public Iterator<T> iterator() {
953 return Iterators.limit(iterable.iterator(), limitSize);
954 }
955 };
956 }
957
958 /**
959 * Returns a view of the supplied iterable that wraps each generated
960 * {@link Iterator} through {@link Iterators#consumingIterator(Iterator)}.
961 *
962 * <p>Note: If {@code iterable} is a {@link Queue}, the returned iterable will
963 * get entries from {@link Queue#remove()} since {@link Queue}'s iteration
964 * order is undefined. Calling {@link Iterator#hasNext()} on a generated
965 * iterator from the returned iterable may cause an item to be immediately
966 * dequeued for return on a subsequent call to {@link Iterator#next()}.
967 *
968 * @param iterable the iterable to wrap
969 * @return a view of the supplied iterable that wraps each generated iterator
970 * through {@link Iterators#consumingIterator(Iterator)}; for queues,
971 * an iterable that generates iterators that return and consume the
972 * queue's elements in queue order
973 *
974 * @see Iterators#consumingIterator(Iterator)
975 * @since 2.0
976 */
977 public static <T> Iterable<T> consumingIterable(final Iterable<T> iterable) {
978 if (iterable instanceof Queue) {
979 return new FluentIterable<T>() {
980 @Override
981 public Iterator<T> iterator() {
982 return new ConsumingQueueIterator<T>((Queue<T>) iterable);
983 }
984 };
985 }
986
987 checkNotNull(iterable);
988
989 return new FluentIterable<T>() {
990 @Override
991 public Iterator<T> iterator() {
992 return Iterators.consumingIterator(iterable.iterator());
993 }
994 };
995 }
996
997 private static class ConsumingQueueIterator<T> extends AbstractIterator<T> {
998 private final Queue<T> queue;
999
1000 private ConsumingQueueIterator(Queue<T> queue) {
1001 this.queue = queue;
1002 }
1003
1004 @Override public T computeNext() {
1005 try {
1006 return queue.remove();
1007 } catch (NoSuchElementException e) {
1008 return endOfData();
1009 }
1010 }
1011 }
1012
1013 // Methods only in Iterables, not in Iterators
1014
1015 /**
1016 * Determines if the given iterable contains no elements.
1017 *
1018 * <p>There is no precise {@link Iterator} equivalent to this method, since
1019 * one can only ask an iterator whether it has any elements <i>remaining</i>
1020 * (which one does using {@link Iterator#hasNext}).
1021 *
1022 * @return {@code true} if the iterable contains no elements
1023 */
1024 public static boolean isEmpty(Iterable<?> iterable) {
1025 if (iterable instanceof Collection) {
1026 return ((Collection<?>) iterable).isEmpty();
1027 }
1028 return !iterable.iterator().hasNext();
1029 }
1030
1031 /**
1032 * Returns an iterable over the merged contents of all given
1033 * {@code iterables}. Equivalent entries will not be de-duplicated.
1034 *
1035 * <p>Callers must ensure that the source {@code iterables} are in
1036 * non-descending order as this method does not sort its input.
1037 *
1038 * <p>For any equivalent elements across all {@code iterables}, it is
1039 * undefined which element is returned first.
1040 *
1041 * @since 11.0
1042 */
1043 @Beta
1044 public static <T> Iterable<T> mergeSorted(
1045 final Iterable<? extends Iterable<? extends T>> iterables,
1046 final Comparator<? super T> comparator) {
1047 checkNotNull(iterables, "iterables");
1048 checkNotNull(comparator, "comparator");
1049 Iterable<T> iterable = new FluentIterable<T>() {
1050 @Override
1051 public Iterator<T> iterator() {
1052 return Iterators.mergeSorted(
1053 Iterables.transform(iterables, Iterables.<T>toIterator()),
1054 comparator);
1055 }
1056 };
1057 return new UnmodifiableIterable<T>(iterable);
1058 }
1059
1060 // TODO(user): Is this the best place for this? Move to fluent functions?
1061 // Useful as a public method?
1062 private static <T> Function<Iterable<? extends T>, Iterator<? extends T>>
1063 toIterator() {
1064 return new Function<Iterable<? extends T>, Iterator<? extends T>>() {
1065 @Override
1066 public Iterator<? extends T> apply(Iterable<? extends T> iterable) {
1067 return iterable.iterator();
1068 }
1069 };
1070 }
1071 }