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.VisibleForTesting;
025 import com.google.common.base.Function;
026
027 import java.util.Arrays;
028 import java.util.Collections;
029 import java.util.Comparator;
030 import java.util.HashSet;
031 import java.util.Iterator;
032 import java.util.List;
033 import java.util.Map;
034 import java.util.NoSuchElementException;
035 import java.util.SortedMap;
036 import java.util.SortedSet;
037 import java.util.TreeSet;
038 import java.util.concurrent.atomic.AtomicInteger;
039
040 import javax.annotation.Nullable;
041
042 /**
043 * A comparator, with additional methods to support common operations. This is
044 * an "enriched" version of {@code Comparator}, in the same sense that {@link
045 * FluentIterable} is an enriched {@link Iterable}). For example: <pre> {@code
046 *
047 * if (Ordering.from(comparator).reverse().isOrdered(list)) { ... }}</pre>
048 *
049 * The {@link #from(Comparator)} method returns the equivalent {@code Ordering}
050 * instance for a pre-existing comparator. You can also skip the comparator step
051 * and extend {@code Ordering} directly: <pre> {@code
052 *
053 * Ordering<String> byLengthOrdering = new Ordering<String>() {
054 * public int compare(String left, String right) {
055 * return Ints.compare(left.length(), right.length());
056 * }
057 * };}</pre>
058 *
059 * Except as noted, the orderings returned by the factory methods of this
060 * class are serializable if and only if the provided instances that back them
061 * are. For example, if {@code ordering} and {@code function} can themselves be
062 * serialized, then {@code ordering.onResultOf(function)} can as well.
063 *
064 * <p>See the Guava User Guide article on <a href=
065 * "http://code.google.com/p/guava-libraries/wiki/OrderingExplained">
066 * {@code Ordering}</a>.
067 *
068 * @author Jesse Wilson
069 * @author Kevin Bourrillion
070 * @since 2.0 (imported from Google Collections Library)
071 */
072 @GwtCompatible
073 public abstract class Ordering<T> implements Comparator<T> {
074 // Natural order
075
076 /**
077 * Returns a serializable ordering that uses the natural order of the values.
078 * The ordering throws a {@link NullPointerException} when passed a null
079 * parameter.
080 *
081 * <p>The type specification is {@code <C extends Comparable>}, instead of
082 * the technically correct {@code <C extends Comparable<? super C>>}, to
083 * support legacy types from before Java 5.
084 */
085 @GwtCompatible(serializable = true)
086 @SuppressWarnings("unchecked") // TODO(kevinb): right way to explain this??
087 public static <C extends Comparable> Ordering<C> natural() {
088 return (Ordering<C>) NaturalOrdering.INSTANCE;
089 }
090
091 // Static factories
092
093 /**
094 * Returns an ordering based on an <i>existing</i> comparator instance. Note
095 * that there's no need to create a <i>new</i> comparator just to pass it in
096 * here; simply subclass {@code Ordering} and implement its {@code compareTo}
097 * method directly instead.
098 *
099 * @param comparator the comparator that defines the order
100 * @return comparator itself if it is already an {@code Ordering}; otherwise
101 * an ordering that wraps that comparator
102 */
103 @GwtCompatible(serializable = true)
104 public static <T> Ordering<T> from(Comparator<T> comparator) {
105 return (comparator instanceof Ordering)
106 ? (Ordering<T>) comparator
107 : new ComparatorOrdering<T>(comparator);
108 }
109
110 /**
111 * Simply returns its argument.
112 *
113 * @deprecated no need to use this
114 */
115 @GwtCompatible(serializable = true)
116 @Deprecated public static <T> Ordering<T> from(Ordering<T> ordering) {
117 return checkNotNull(ordering);
118 }
119
120 /**
121 * Returns an ordering that compares objects according to the order in
122 * which they appear in the given list. Only objects present in the list
123 * (according to {@link Object#equals}) may be compared. This comparator
124 * imposes a "partial ordering" over the type {@code T}. Subsequent changes
125 * to the {@code valuesInOrder} list will have no effect on the returned
126 * comparator. Null values in the list are not supported.
127 *
128 * <p>The returned comparator throws an {@link ClassCastException} when it
129 * receives an input parameter that isn't among the provided values.
130 *
131 * <p>The generated comparator is serializable if all the provided values are
132 * serializable.
133 *
134 * @param valuesInOrder the values that the returned comparator will be able
135 * to compare, in the order the comparator should induce
136 * @return the comparator described above
137 * @throws NullPointerException if any of the provided values is null
138 * @throws IllegalArgumentException if {@code valuesInOrder} contains any
139 * duplicate values (according to {@link Object#equals})
140 */
141 @GwtCompatible(serializable = true)
142 public static <T> Ordering<T> explicit(List<T> valuesInOrder) {
143 return new ExplicitOrdering<T>(valuesInOrder);
144 }
145
146 /**
147 * Returns an ordering that compares objects according to the order in
148 * which they are given to this method. Only objects present in the argument
149 * list (according to {@link Object#equals}) may be compared. This comparator
150 * imposes a "partial ordering" over the type {@code T}. Null values in the
151 * argument list are not supported.
152 *
153 * <p>The returned comparator throws a {@link ClassCastException} when it
154 * receives an input parameter that isn't among the provided values.
155 *
156 * <p>The generated comparator is serializable if all the provided values are
157 * serializable.
158 *
159 * @param leastValue the value which the returned comparator should consider
160 * the "least" of all values
161 * @param remainingValuesInOrder the rest of the values that the returned
162 * comparator will be able to compare, in the order the comparator should
163 * follow
164 * @return the comparator described above
165 * @throws NullPointerException if any of the provided values is null
166 * @throws IllegalArgumentException if any duplicate values (according to
167 * {@link Object#equals(Object)}) are present among the method arguments
168 */
169 @GwtCompatible(serializable = true)
170 public static <T> Ordering<T> explicit(
171 T leastValue, T... remainingValuesInOrder) {
172 return explicit(Lists.asList(leastValue, remainingValuesInOrder));
173 }
174
175 // Ordering<Object> singletons
176
177 /**
178 * Returns an ordering which treats all values as equal, indicating "no
179 * ordering." Passing this ordering to any <i>stable</i> sort algorithm
180 * results in no change to the order of elements. Note especially that {@link
181 * #sortedCopy} and {@link #immutableSortedCopy} are stable, and in the
182 * returned instance these are implemented by simply copying the source list.
183 *
184 * <p>Example: <pre> {@code
185 *
186 * Ordering.allEqual().nullsLast().sortedCopy(
187 * asList(t, null, e, s, null, t, null))}</pre>
188 *
189 * Assuming {@code t}, {@code e} and {@code s} are non-null, this returns
190 * {@code [t, e, s, t, null, null, null]} regardlesss of the true comparison
191 * order of those three values (which might not even implement {@link
192 * Comparable} at all).
193 *
194 * <p><b>Warning:</b> by definition, this comparator is not <i>consistent with
195 * equals</i> (as defined {@linkplain Comparator here}). Avoid its use in
196 * APIs, such as {@link TreeSet#TreeSet(Comparator)}, where such consistency
197 * is expected.
198 *
199 * <p>The returned comparator is serializable.
200 */
201 @GwtCompatible(serializable = true)
202 @SuppressWarnings("unchecked")
203 public static Ordering<Object> allEqual() {
204 return AllEqualOrdering.INSTANCE;
205 }
206
207 /**
208 * Returns an ordering that compares objects by the natural ordering of their
209 * string representations as returned by {@code toString()}. It does not
210 * support null values.
211 *
212 * <p>The comparator is serializable.
213 */
214 @GwtCompatible(serializable = true)
215 public static Ordering<Object> usingToString() {
216 return UsingToStringOrdering.INSTANCE;
217 }
218
219 /**
220 * Returns an arbitrary ordering over all objects, for which {@code compare(a,
221 * b) == 0} implies {@code a == b} (identity equality). There is no meaning
222 * whatsoever to the order imposed, but it is constant for the life of the VM.
223 *
224 * <p>Because the ordering is identity-based, it is not "consistent with
225 * {@link Object#equals(Object)}" as defined by {@link Comparator}. Use
226 * caution when building a {@link SortedSet} or {@link SortedMap} from it, as
227 * the resulting collection will not behave exactly according to spec.
228 *
229 * <p>This ordering is not serializable, as its implementation relies on
230 * {@link System#identityHashCode(Object)}, so its behavior cannot be
231 * preserved across serialization.
232 *
233 * @since 2.0
234 */
235 public static Ordering<Object> arbitrary() {
236 return ArbitraryOrderingHolder.ARBITRARY_ORDERING;
237 }
238
239 private static class ArbitraryOrderingHolder {
240 static final Ordering<Object> ARBITRARY_ORDERING = new ArbitraryOrdering();
241 }
242
243 @VisibleForTesting static class ArbitraryOrdering extends Ordering<Object> {
244 @SuppressWarnings("deprecation") // TODO(kevinb): ?
245 private Map<Object, Integer> uids =
246 Platform.tryWeakKeys(new MapMaker()).makeComputingMap(
247 new Function<Object, Integer>() {
248 final AtomicInteger counter = new AtomicInteger(0);
249 @Override
250 public Integer apply(Object from) {
251 return counter.getAndIncrement();
252 }
253 });
254
255 @Override public int compare(Object left, Object right) {
256 if (left == right) {
257 return 0;
258 } else if (left == null) {
259 return -1;
260 } else if (right == null) {
261 return 1;
262 }
263 int leftCode = identityHashCode(left);
264 int rightCode = identityHashCode(right);
265 if (leftCode != rightCode) {
266 return leftCode < rightCode ? -1 : 1;
267 }
268
269 // identityHashCode collision (rare, but not as rare as you'd think)
270 int result = uids.get(left).compareTo(uids.get(right));
271 if (result == 0) {
272 throw new AssertionError(); // extremely, extremely unlikely.
273 }
274 return result;
275 }
276
277 @Override public String toString() {
278 return "Ordering.arbitrary()";
279 }
280
281 /*
282 * We need to be able to mock identityHashCode() calls for tests, because it
283 * can take 1-10 seconds to find colliding objects. Mocking frameworks that
284 * can do magic to mock static method calls still can't do so for a system
285 * class, so we need the indirection. In production, Hotspot should still
286 * recognize that the call is 1-morphic and should still be willing to
287 * inline it if necessary.
288 */
289 int identityHashCode(Object object) {
290 return System.identityHashCode(object);
291 }
292 }
293
294 // Constructor
295
296 /**
297 * Constructs a new instance of this class (only invokable by the subclass
298 * constructor, typically implicit).
299 */
300 protected Ordering() {}
301
302 // Instance-based factories (and any static equivalents)
303
304 /**
305 * Returns the reverse of this ordering; the {@code Ordering} equivalent to
306 * {@link Collections#reverseOrder(Comparator)}.
307 */
308 // type parameter <S> lets us avoid the extra <String> in statements like:
309 // Ordering<String> o = Ordering.<String>natural().reverse();
310 @GwtCompatible(serializable = true)
311 public <S extends T> Ordering<S> reverse() {
312 return new ReverseOrdering<S>(this);
313 }
314
315 /**
316 * Returns an ordering that treats {@code null} as less than all other values
317 * and uses {@code this} to compare non-null values.
318 */
319 // type parameter <S> lets us avoid the extra <String> in statements like:
320 // Ordering<String> o = Ordering.<String>natural().nullsFirst();
321 @GwtCompatible(serializable = true)
322 public <S extends T> Ordering<S> nullsFirst() {
323 return new NullsFirstOrdering<S>(this);
324 }
325
326 /**
327 * Returns an ordering that treats {@code null} as greater than all other
328 * values and uses this ordering to compare non-null values.
329 */
330 // type parameter <S> lets us avoid the extra <String> in statements like:
331 // Ordering<String> o = Ordering.<String>natural().nullsLast();
332 @GwtCompatible(serializable = true)
333 public <S extends T> Ordering<S> nullsLast() {
334 return new NullsLastOrdering<S>(this);
335 }
336
337 /**
338 * Returns a new ordering on {@code F} which orders elements by first applying
339 * a function to them, then comparing those results using {@code this}. For
340 * example, to compare objects by their string forms, in a case-insensitive
341 * manner, use: <pre> {@code
342 *
343 * Ordering.from(String.CASE_INSENSITIVE_ORDER)
344 * .onResultOf(Functions.toStringFunction())}</pre>
345 */
346 @GwtCompatible(serializable = true)
347 public <F> Ordering<F> onResultOf(Function<F, ? extends T> function) {
348 return new ByFunctionOrdering<F, T>(function, this);
349 }
350
351 /**
352 * Returns an ordering which first uses the ordering {@code this}, but which
353 * in the event of a "tie", then delegates to {@code secondaryComparator}.
354 * For example, to sort a bug list first by status and second by priority, you
355 * might use {@code byStatus.compound(byPriority)}. For a compound ordering
356 * with three or more components, simply chain multiple calls to this method.
357 *
358 * <p>An ordering produced by this method, or a chain of calls to this method,
359 * is equivalent to one created using {@link Ordering#compound(Iterable)} on
360 * the same component comparators.
361 */
362 @GwtCompatible(serializable = true)
363 public <U extends T> Ordering<U> compound(
364 Comparator<? super U> secondaryComparator) {
365 return new CompoundOrdering<U>(this, checkNotNull(secondaryComparator));
366 }
367
368 /**
369 * Returns an ordering which tries each given comparator in order until a
370 * non-zero result is found, returning that result, and returning zero only if
371 * all comparators return zero. The returned ordering is based on the state of
372 * the {@code comparators} iterable at the time it was provided to this
373 * method.
374 *
375 * <p>The returned ordering is equivalent to that produced using {@code
376 * Ordering.from(comp1).compound(comp2).compound(comp3) . . .}.
377 *
378 * <p><b>Warning:</b> Supplying an argument with undefined iteration order,
379 * such as a {@link HashSet}, will produce non-deterministic results.
380 *
381 * @param comparators the comparators to try in order
382 */
383 @GwtCompatible(serializable = true)
384 public static <T> Ordering<T> compound(
385 Iterable<? extends Comparator<? super T>> comparators) {
386 return new CompoundOrdering<T>(comparators);
387 }
388
389 /**
390 * Returns a new ordering which sorts iterables by comparing corresponding
391 * elements pairwise until a nonzero result is found; imposes "dictionary
392 * order". If the end of one iterable is reached, but not the other, the
393 * shorter iterable is considered to be less than the longer one. For example,
394 * a lexicographical natural ordering over integers considers {@code
395 * [] < [1] < [1, 1] < [1, 2] < [2]}.
396 *
397 * <p>Note that {@code ordering.lexicographical().reverse()} is not
398 * equivalent to {@code ordering.reverse().lexicographical()} (consider how
399 * each would order {@code [1]} and {@code [1, 1]}).
400 *
401 * @since 2.0
402 */
403 @GwtCompatible(serializable = true)
404 // type parameter <S> lets us avoid the extra <String> in statements like:
405 // Ordering<Iterable<String>> o =
406 // Ordering.<String>natural().lexicographical();
407 public <S extends T> Ordering<Iterable<S>> lexicographical() {
408 /*
409 * Note that technically the returned ordering should be capable of
410 * handling not just {@code Iterable<S>} instances, but also any {@code
411 * Iterable<? extends S>}. However, the need for this comes up so rarely
412 * that it doesn't justify making everyone else deal with the very ugly
413 * wildcard.
414 */
415 return new LexicographicalOrdering<S>(this);
416 }
417
418 // Regular instance methods
419
420 // Override to add @Nullable
421 @Override public abstract int compare(@Nullable T left, @Nullable T right);
422
423 /**
424 * Returns the least of the specified values according to this ordering. If
425 * there are multiple least values, the first of those is returned. The
426 * iterator will be left exhausted: its {@code hasNext()} method will return
427 * {@code false}.
428 *
429 * @param iterator the iterator whose minimum element is to be determined
430 * @throws NoSuchElementException if {@code iterator} is empty
431 * @throws ClassCastException if the parameters are not <i>mutually
432 * comparable</i> under this ordering.
433 *
434 * @since 11.0
435 */
436 @Beta
437 public <E extends T> E min(Iterator<E> iterator) {
438 // let this throw NoSuchElementException as necessary
439 E minSoFar = iterator.next();
440
441 while (iterator.hasNext()) {
442 minSoFar = min(minSoFar, iterator.next());
443 }
444
445 return minSoFar;
446 }
447
448 /**
449 * Returns the least of the specified values according to this ordering. If
450 * there are multiple least values, the first of those is returned.
451 *
452 * @param iterable the iterable whose minimum element is to be determined
453 * @throws NoSuchElementException if {@code iterable} is empty
454 * @throws ClassCastException if the parameters are not <i>mutually
455 * comparable</i> under this ordering.
456 */
457 public <E extends T> E min(Iterable<E> iterable) {
458 return min(iterable.iterator());
459 }
460
461 /**
462 * Returns the lesser of the two values according to this ordering. If the
463 * values compare as 0, the first is returned.
464 *
465 * <p><b>Implementation note:</b> this method is invoked by the default
466 * implementations of the other {@code min} overloads, so overriding it will
467 * affect their behavior.
468 *
469 * @param a value to compare, returned if less than or equal to b.
470 * @param b value to compare.
471 * @throws ClassCastException if the parameters are not <i>mutually
472 * comparable</i> under this ordering.
473 */
474 public <E extends T> E min(@Nullable E a, @Nullable E b) {
475 return compare(a, b) <= 0 ? a : b;
476 }
477
478 /**
479 * Returns the least of the specified values according to this ordering. If
480 * there are multiple least values, the first of those is returned.
481 *
482 * @param a value to compare, returned if less than or equal to the rest.
483 * @param b value to compare
484 * @param c value to compare
485 * @param rest values to compare
486 * @throws ClassCastException if the parameters are not <i>mutually
487 * comparable</i> under this ordering.
488 */
489 public <E extends T> E min(
490 @Nullable E a, @Nullable E b, @Nullable E c, E... rest) {
491 E minSoFar = min(min(a, b), c);
492
493 for (E r : rest) {
494 minSoFar = min(minSoFar, r);
495 }
496
497 return minSoFar;
498 }
499
500 /**
501 * Returns the greatest of the specified values according to this ordering. If
502 * there are multiple greatest values, the first of those is returned. The
503 * iterator will be left exhausted: its {@code hasNext()} method will return
504 * {@code false}.
505 *
506 * @param iterator the iterator whose maximum element is to be determined
507 * @throws NoSuchElementException if {@code iterator} is empty
508 * @throws ClassCastException if the parameters are not <i>mutually
509 * comparable</i> under this ordering.
510 *
511 * @since 11.0
512 */
513 @Beta
514 public <E extends T> E max(Iterator<E> iterator) {
515 // let this throw NoSuchElementException as necessary
516 E maxSoFar = iterator.next();
517
518 while (iterator.hasNext()) {
519 maxSoFar = max(maxSoFar, iterator.next());
520 }
521
522 return maxSoFar;
523 }
524
525 /**
526 * Returns the greatest of the specified values according to this ordering. If
527 * there are multiple greatest values, the first of those is returned.
528 *
529 * @param iterable the iterable whose maximum element is to be determined
530 * @throws NoSuchElementException if {@code iterable} is empty
531 * @throws ClassCastException if the parameters are not <i>mutually
532 * comparable</i> under this ordering.
533 */
534 public <E extends T> E max(Iterable<E> iterable) {
535 return max(iterable.iterator());
536 }
537
538 /**
539 * Returns the greater of the two values according to this ordering. If the
540 * values compare as 0, the first is returned.
541 *
542 * <p><b>Implementation note:</b> this method is invoked by the default
543 * implementations of the other {@code max} overloads, so overriding it will
544 * affect their behavior.
545 *
546 * @param a value to compare, returned if greater than or equal to b.
547 * @param b value to compare.
548 * @throws ClassCastException if the parameters are not <i>mutually
549 * comparable</i> under this ordering.
550 */
551 public <E extends T> E max(@Nullable E a, @Nullable E b) {
552 return compare(a, b) >= 0 ? a : b;
553 }
554
555 /**
556 * Returns the greatest of the specified values according to this ordering. If
557 * there are multiple greatest values, the first of those is returned.
558 *
559 * @param a value to compare, returned if greater than or equal to the rest.
560 * @param b value to compare
561 * @param c value to compare
562 * @param rest values to compare
563 * @throws ClassCastException if the parameters are not <i>mutually
564 * comparable</i> under this ordering.
565 */
566 public <E extends T> E max(
567 @Nullable E a, @Nullable E b, @Nullable E c, E... rest) {
568 E maxSoFar = max(max(a, b), c);
569
570 for (E r : rest) {
571 maxSoFar = max(maxSoFar, r);
572 }
573
574 return maxSoFar;
575 }
576
577 /**
578 * Returns the {@code k} least elements of the given iterable according to
579 * this ordering, in order from least to greatest. If there are fewer than
580 * {@code k} elements present, all will be included.
581 *
582 * <p>The implementation does not necessarily use a <i>stable</i> sorting
583 * algorithm; when multiple elements are equivalent, it is undefined which
584 * will come first.
585 *
586 * @return an immutable {@code RandomAccess} list of the {@code k} least
587 * elements in ascending order
588 * @throws IllegalArgumentException if {@code k} is negative
589 * @since 8.0
590 */
591 @Beta
592 public <E extends T> List<E> leastOf(Iterable<E> iterable, int k) {
593 checkArgument(k >= 0, "%d is negative", k);
594
595 // values is not an E[], but we use it as such for readability. Hack.
596 @SuppressWarnings("unchecked")
597 E[] values = (E[]) Iterables.toArray(iterable);
598
599 // TODO(nshupe): also sort whole list if k is *near* values.length?
600 // TODO(kevinb): benchmark this impl against hand-coded heap
601 E[] resultArray;
602 if (values.length <= k) {
603 Arrays.sort(values, this);
604 resultArray = values;
605 } else {
606 quicksortLeastK(values, 0, values.length - 1, k);
607
608 // this is not an E[], but we use it as such for readability. Hack.
609 @SuppressWarnings("unchecked")
610 E[] tmp = (E[]) new Object[k];
611 resultArray = tmp;
612 System.arraycopy(values, 0, resultArray, 0, k);
613 }
614
615 return Collections.unmodifiableList(Arrays.asList(resultArray));
616 }
617
618 /**
619 * Returns the {@code k} greatest elements of the given iterable according to
620 * this ordering, in order from greatest to least. If there are fewer than
621 * {@code k} elements present, all will be included.
622 *
623 * <p>The implementation does not necessarily use a <i>stable</i> sorting
624 * algorithm; when multiple elements are equivalent, it is undefined which
625 * will come first.
626 *
627 * @return an immutable {@code RandomAccess} list of the {@code k} greatest
628 * elements in <i>descending order</i>
629 * @throws IllegalArgumentException if {@code k} is negative
630 * @since 8.0
631 */
632 @Beta
633 public <E extends T> List<E> greatestOf(Iterable<E> iterable, int k) {
634 // TODO(kevinb): see if delegation is hurting performance noticeably
635 // TODO(kevinb): if we change this implementation, add full unit tests.
636 return reverse().leastOf(iterable, k);
637 }
638
639 private <E extends T> void quicksortLeastK(
640 E[] values, int left, int right, int k) {
641 if (right > left) {
642 int pivotIndex = (left + right) >>> 1; // left + ((right - left) / 2)
643 int pivotNewIndex = partition(values, left, right, pivotIndex);
644 quicksortLeastK(values, left, pivotNewIndex - 1, k);
645 if (pivotNewIndex < k) {
646 quicksortLeastK(values, pivotNewIndex + 1, right, k);
647 }
648 }
649 }
650
651 private <E extends T> int partition(
652 E[] values, int left, int right, int pivotIndex) {
653 E pivotValue = values[pivotIndex];
654
655 values[pivotIndex] = values[right];
656 values[right] = pivotValue;
657
658 int storeIndex = left;
659 for (int i = left; i < right; i++) {
660 if (compare(values[i], pivotValue) < 0) {
661 ObjectArrays.swap(values, storeIndex, i);
662 storeIndex++;
663 }
664 }
665 ObjectArrays.swap(values, right, storeIndex);
666 return storeIndex;
667 }
668
669 /**
670 * Returns a copy of the given iterable sorted by this ordering. The input is
671 * not modified. The returned list is modifiable, serializable, and has random
672 * access.
673 *
674 * <p>Unlike {@link Sets#newTreeSet(Iterable)}, this method does not discard
675 * elements that are duplicates according to the comparator. The sort
676 * performed is <i>stable</i>, meaning that such elements will appear in the
677 * resulting list in the same order they appeared in the input.
678 *
679 * @param iterable the elements to be copied and sorted
680 * @return a new list containing the given elements in sorted order
681 */
682 public <E extends T> List<E> sortedCopy(Iterable<E> iterable) {
683 @SuppressWarnings("unchecked") // does not escape, and contains only E's
684 E[] array = (E[]) Iterables.toArray(iterable);
685 Arrays.sort(array, this);
686 return Lists.newArrayList(Arrays.asList(array));
687 }
688
689 /**
690 * Returns an <i>immutable</i> copy of the given iterable sorted by this
691 * ordering. The input is not modified.
692 *
693 * <p>Unlike {@link Sets#newTreeSet(Iterable)}, this method does not discard
694 * elements that are duplicates according to the comparator. The sort
695 * performed is <i>stable</i>, meaning that such elements will appear in the
696 * resulting list in the same order they appeared in the input.
697 *
698 * @param iterable the elements to be copied and sorted
699 * @return a new immutable list containing the given elements in sorted order
700 * @throws NullPointerException if {@code iterable} or any of its elements is
701 * null
702 * @since 3.0
703 */
704 public <E extends T> ImmutableList<E> immutableSortedCopy(
705 Iterable<E> iterable) {
706 @SuppressWarnings("unchecked") // we'll only ever have E's in here
707 E[] elements = (E[]) Iterables.toArray(iterable);
708 for (E e : elements) {
709 checkNotNull(e);
710 }
711 Arrays.sort(elements, this);
712 return ImmutableList.asImmutableList(elements);
713 }
714
715 /**
716 * Returns {@code true} if each element in {@code iterable} after the first is
717 * greater than or equal to the element that preceded it, according to this
718 * ordering. Note that this is always true when the iterable has fewer than
719 * two elements.
720 */
721 public boolean isOrdered(Iterable<? extends T> iterable) {
722 Iterator<? extends T> it = iterable.iterator();
723 if (it.hasNext()) {
724 T prev = it.next();
725 while (it.hasNext()) {
726 T next = it.next();
727 if (compare(prev, next) > 0) {
728 return false;
729 }
730 prev = next;
731 }
732 }
733 return true;
734 }
735
736 /**
737 * Returns {@code true} if each element in {@code iterable} after the first is
738 * <i>strictly</i> greater than the element that preceded it, according to
739 * this ordering. Note that this is always true when the iterable has fewer
740 * than two elements.
741 */
742 public boolean isStrictlyOrdered(Iterable<? extends T> iterable) {
743 Iterator<? extends T> it = iterable.iterator();
744 if (it.hasNext()) {
745 T prev = it.next();
746 while (it.hasNext()) {
747 T next = it.next();
748 if (compare(prev, next) >= 0) {
749 return false;
750 }
751 prev = next;
752 }
753 }
754 return true;
755 }
756
757 /**
758 * {@link Collections#binarySearch(List, Object, Comparator) Searches}
759 * {@code sortedList} for {@code key} using the binary search algorithm. The
760 * list must be sorted using this ordering.
761 *
762 * @param sortedList the list to be searched
763 * @param key the key to be searched for
764 */
765 public int binarySearch(List<? extends T> sortedList, @Nullable T key) {
766 return Collections.binarySearch(sortedList, key, this);
767 }
768
769 /**
770 * Exception thrown by a {@link Ordering#explicit(List)} or {@link
771 * Ordering#explicit(Object, Object[])} comparator when comparing a value
772 * outside the set of values it can compare. Extending {@link
773 * ClassCastException} may seem odd, but it is required.
774 */
775 // TODO(kevinb): make this public, document it right
776 @VisibleForTesting
777 static class IncomparableValueException extends ClassCastException {
778 final Object value;
779
780 IncomparableValueException(Object value) {
781 super("Cannot compare value: " + value);
782 this.value = value;
783 }
784
785 private static final long serialVersionUID = 0;
786 }
787
788 // Never make these public
789 static final int LEFT_IS_GREATER = 1;
790 static final int RIGHT_IS_GREATER = -1;
791 }