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.concurrent.atomic.AtomicInteger;
038
039 import javax.annotation.Nullable;
040
041 /**
042 * A comparator with added methods to support common functions. For example:
043 * <pre> {@code
044 *
045 * if (Ordering.from(comparator).reverse().isOrdered(list)) { ... }}</pre>
046 *
047 * The {@link #from(Comparator)} method returns the equivalent {@code Ordering}
048 * instance for a pre-existing comparator. You can also skip the comparator step
049 * and extend {@code Ordering} directly: <pre> {@code
050 *
051 * Ordering<String> byLengthOrdering = new Ordering<String>() {
052 * public int compare(String left, String right) {
053 * return Ints.compare(left.length(), right.length());
054 * }
055 * };}</pre>
056 *
057 * Except as noted, the orderings returned by the factory methods of this
058 * class are serializable if and only if the provided instances that back them
059 * are. For example, if {@code ordering} and {@code function} can themselves be
060 * serialized, then {@code ordering.onResultOf(function)} can as well.
061 *
062 * @author Jesse Wilson
063 * @author Kevin Bourrillion
064 * @since 2 (imported from Google Collections Library)
065 */
066 @GwtCompatible
067 public abstract class Ordering<T> implements Comparator<T> {
068 // Static factories
069
070 /**
071 * Returns a serializable ordering that uses the natural order of the values.
072 * The ordering throws a {@link NullPointerException} when passed a null
073 * parameter.
074 *
075 * <p>The type specification is {@code <C extends Comparable>}, instead of
076 * the technically correct {@code <C extends Comparable<? super C>>}, to
077 * support legacy types from before Java 5.
078 */
079 @GwtCompatible(serializable = true)
080 @SuppressWarnings("unchecked") // TODO(kevinb): the right way to explain this??
081 public static <C extends Comparable> Ordering<C> natural() {
082 return (Ordering<C>) NaturalOrdering.INSTANCE;
083 }
084
085 /**
086 * Returns an ordering for a pre-existing {@code comparator}. Note
087 * that if the comparator is not pre-existing, and you don't require
088 * serialization, you can subclass {@code Ordering} and implement its
089 * {@link #compare(Object, Object) compare} method instead.
090 *
091 * @param comparator the comparator that defines the order
092 */
093 @GwtCompatible(serializable = true)
094 public static <T> Ordering<T> from(Comparator<T> comparator) {
095 return (comparator instanceof Ordering)
096 ? (Ordering<T>) comparator
097 : new ComparatorOrdering<T>(comparator);
098 }
099
100 /**
101 * Simply returns its argument.
102 *
103 * @deprecated no need to use this
104 */
105 @GwtCompatible(serializable = true)
106 @Deprecated public static <T> Ordering<T> from(Ordering<T> ordering) {
107 return checkNotNull(ordering);
108 }
109
110 /**
111 * Returns an ordering that compares objects according to the order in
112 * which they appear in the given list. Only objects present in the list
113 * (according to {@link Object#equals}) may be compared. This comparator
114 * imposes a "partial ordering" over the type {@code T}. Subsequent changes
115 * to the {@code valuesInOrder} list will have no effect on the returned
116 * comparator. Null values in the list are not supported.
117 *
118 * <p>The returned comparator throws an {@link ClassCastException} when it
119 * receives an input parameter that isn't among the provided values.
120 *
121 * <p>The generated comparator is serializable if all the provided values are
122 * serializable.
123 *
124 * @param valuesInOrder the values that the returned comparator will be able
125 * to compare, in the order the comparator should induce
126 * @return the comparator described above
127 * @throws NullPointerException if any of the provided values is null
128 * @throws IllegalArgumentException if {@code valuesInOrder} contains any
129 * duplicate values (according to {@link Object#equals})
130 */
131 @GwtCompatible(serializable = true)
132 public static <T> Ordering<T> explicit(List<T> valuesInOrder) {
133 return new ExplicitOrdering<T>(valuesInOrder);
134 }
135
136 /**
137 * Returns an ordering that compares objects according to the order in
138 * which they are given to this method. Only objects present in the argument
139 * list (according to {@link Object#equals}) may be compared. This comparator
140 * imposes a "partial ordering" over the type {@code T}. Null values in the
141 * argument list are not supported.
142 *
143 * <p>The returned comparator throws a {@link ClassCastException} when it
144 * receives an input parameter that isn't among the provided values.
145 *
146 * <p>The generated comparator is serializable if all the provided values are
147 * serializable.
148 *
149 * @param leastValue the value which the returned comparator should consider
150 * the "least" of all values
151 * @param remainingValuesInOrder the rest of the values that the returned
152 * comparator will be able to compare, in the order the comparator should
153 * follow
154 * @return the comparator described above
155 * @throws NullPointerException if any of the provided values is null
156 * @throws IllegalArgumentException if any duplicate values (according to
157 * {@link Object#equals(Object)}) are present among the method arguments
158 */
159 @GwtCompatible(serializable = true)
160 public static <T> Ordering<T> explicit(
161 T leastValue, T... remainingValuesInOrder) {
162 return explicit(Lists.asList(leastValue, remainingValuesInOrder));
163 }
164
165 /**
166 * Exception thrown by a {@link Ordering#explicit(List)} or {@link
167 * Ordering#explicit(Object, Object[])} comparator when comparing a value
168 * outside the set of values it can compare. Extending {@link
169 * ClassCastException} may seem odd, but it is required.
170 */
171 // TODO(kevinb): make this public, document it right
172 @VisibleForTesting
173 static class IncomparableValueException extends ClassCastException {
174 final Object value;
175
176 IncomparableValueException(Object value) {
177 super("Cannot compare value: " + value);
178 this.value = value;
179 }
180
181 private static final long serialVersionUID = 0;
182 }
183
184 /**
185 * Returns an arbitrary ordering over all objects, for which {@code compare(a,
186 * b) == 0} implies {@code a == b} (identity equality). There is no meaning
187 * whatsoever to the order imposed, but it is constant for the life of the VM.
188 *
189 * <p>Because the ordering is identity-based, it is not "consistent with
190 * {@link Object#equals(Object)}" as defined by {@link Comparator}. Use
191 * caution when building a {@link SortedSet} or {@link SortedMap} from it, as
192 * the resulting collection will not behave exactly according to spec.
193 *
194 * <p>This ordering is not serializable, as its implementation relies on
195 * {@link System#identityHashCode(Object)}, so its behavior cannot be
196 * preserved across serialization.
197 *
198 * @since 2
199 */
200 public static Ordering<Object> arbitrary() {
201 return ArbitraryOrderingHolder.ARBITRARY_ORDERING;
202 }
203
204 private static class ArbitraryOrderingHolder {
205 static final Ordering<Object> ARBITRARY_ORDERING = new ArbitraryOrdering();
206 }
207
208 @VisibleForTesting static class ArbitraryOrdering extends Ordering<Object> {
209 private Map<Object, Integer> uids =
210 Platform.tryWeakKeys(new MapMaker()).makeComputingMap(
211 new Function<Object, Integer>() {
212 final AtomicInteger counter = new AtomicInteger(0);
213 @Override
214 public Integer apply(Object from) {
215 return counter.getAndIncrement();
216 }
217 });
218
219 @Override public int compare(Object left, Object right) {
220 if (left == right) {
221 return 0;
222 }
223 int leftCode = identityHashCode(left);
224 int rightCode = identityHashCode(right);
225 if (leftCode != rightCode) {
226 return leftCode < rightCode ? -1 : 1;
227 }
228
229 // identityHashCode collision (rare, but not as rare as you'd think)
230 int result = uids.get(left).compareTo(uids.get(right));
231 if (result == 0) {
232 throw new AssertionError(); // extremely, extremely unlikely.
233 }
234 return result;
235 }
236
237 @Override public String toString() {
238 return "Ordering.arbitrary()";
239 }
240
241 /*
242 * We need to be able to mock identityHashCode() calls for tests, because it
243 * can take 1-10 seconds to find colliding objects. Mocking frameworks that
244 * can do magic to mock static method calls still can't do so for a system
245 * class, so we need the indirection. In production, Hotspot should still
246 * recognize that the call is 1-morphic and should still be willing to
247 * inline it if necessary.
248 */
249 int identityHashCode(Object object) {
250 return System.identityHashCode(object);
251 }
252 }
253
254 /**
255 * Returns an ordering that compares objects by the natural ordering of their
256 * string representations as returned by {@code toString()}. It does not
257 * support null values.
258 *
259 * <p>The comparator is serializable.
260 */
261 @GwtCompatible(serializable = true)
262 public static Ordering<Object> usingToString() {
263 return UsingToStringOrdering.INSTANCE;
264 }
265
266 /**
267 * Returns an ordering which tries each given comparator in order until a
268 * non-zero result is found, returning that result, and returning zero only if
269 * all comparators return zero. The returned ordering is based on the state of
270 * the {@code comparators} iterable at the time it was provided to this
271 * method.
272 *
273 * <p>The returned ordering is equivalent to that produced using {@code
274 * Ordering.from(comp1).compound(comp2).compound(comp3) . . .}.
275 *
276 * <p><b>Warning:</b> Supplying an argument with undefined iteration order,
277 * such as a {@link HashSet}, will produce non-deterministic results.
278 *
279 * @param comparators the comparators to try in order
280 */
281 @GwtCompatible(serializable = true)
282 public static <T> Ordering<T> compound(
283 Iterable<? extends Comparator<? super T>> comparators) {
284 return new CompoundOrdering<T>(comparators);
285 }
286
287 /**
288 * Constructs a new instance of this class (only invokable by the subclass
289 * constructor, typically implicit).
290 */
291 protected Ordering() {}
292
293 // Non-static factories
294
295 /**
296 * Returns an ordering which first uses the ordering {@code this}, but which
297 * in the event of a "tie", then delegates to {@code secondaryComparator}.
298 * For example, to sort a bug list first by status and second by priority, you
299 * might use {@code byStatus.compound(byPriority)}. For a compound ordering
300 * with three or more components, simply chain multiple calls to this method.
301 *
302 * <p>An ordering produced by this method, or a chain of calls to this method,
303 * is equivalent to one created using {@link Ordering#compound(Iterable)} on
304 * the same component comparators.
305 */
306 @GwtCompatible(serializable = true)
307 public <U extends T> Ordering<U> compound(
308 Comparator<? super U> secondaryComparator) {
309 return new CompoundOrdering<U>(this, checkNotNull(secondaryComparator));
310 }
311
312 /**
313 * Returns the reverse of this ordering; the {@code Ordering} equivalent to
314 * {@link Collections#reverseOrder(Comparator)}.
315 */
316 // type parameter <S> lets us avoid the extra <String> in statements like:
317 // Ordering<String> o = Ordering.<String>natural().reverse();
318 @GwtCompatible(serializable = true)
319 public <S extends T> Ordering<S> reverse() {
320 return new ReverseOrdering<S>(this);
321 }
322
323 /**
324 * Returns a new ordering on {@code F} which orders elements by first applying
325 * a function to them, then comparing those results using {@code this}. For
326 * example, to compare objects by their string forms, in a case-insensitive
327 * manner, use: <pre> {@code
328 *
329 * Ordering.from(String.CASE_INSENSITIVE_ORDER)
330 * .onResultOf(Functions.toStringFunction())}</pre>
331 */
332 @GwtCompatible(serializable = true)
333 public <F> Ordering<F> onResultOf(Function<F, ? extends T> function) {
334 return new ByFunctionOrdering<F, T>(function, this);
335 }
336
337 /**
338 * Returns a new ordering which sorts iterables by comparing corresponding
339 * elements pairwise until a nonzero result is found; imposes "dictionary
340 * order". If the end of one iterable is reached, but not the other, the
341 * shorter iterable is considered to be less than the longer one. For example,
342 * a lexicographical natural ordering over integers considers {@code
343 * [] < [1] < [1, 1] < [1, 2] < [2]}.
344 *
345 * <p>Note that {@code ordering.lexicographical().reverse()} is not
346 * equivalent to {@code ordering.reverse().lexicographical()} (consider how
347 * each would order {@code [1]} and {@code [1, 1]}).
348 *
349 * @since 2
350 */
351 @GwtCompatible(serializable = true)
352 // type parameter <S> lets us avoid the extra <String> in statements like:
353 // Ordering<Iterable<String>> o =
354 // Ordering.<String>natural().lexicographical();
355 public <S extends T> Ordering<Iterable<S>> lexicographical() {
356 /*
357 * Note that technically the returned ordering should be capable of
358 * handling not just {@code Iterable<S>} instances, but also any {@code
359 * Iterable<? extends S>}. However, the need for this comes up so rarely
360 * that it doesn't justify making everyone else deal with the very ugly
361 * wildcard.
362 */
363 return new LexicographicalOrdering<S>(this);
364 }
365
366 /**
367 * Returns an ordering that treats {@code null} as less than all other values
368 * and uses {@code this} to compare non-null values.
369 */
370 // type parameter <S> lets us avoid the extra <String> in statements like:
371 // Ordering<String> o = Ordering.<String>natural().nullsFirst();
372 @GwtCompatible(serializable = true)
373 public <S extends T> Ordering<S> nullsFirst() {
374 return new NullsFirstOrdering<S>(this);
375 }
376
377 /**
378 * Returns an ordering that treats {@code null} as greater than all other
379 * values and uses this ordering to compare non-null values.
380 */
381 // type parameter <S> lets us avoid the extra <String> in statements like:
382 // Ordering<String> o = Ordering.<String>natural().nullsLast();
383 @GwtCompatible(serializable = true)
384 public <S extends T> Ordering<S> nullsLast() {
385 return new NullsLastOrdering<S>(this);
386 }
387
388 // Regular instance methods
389
390 // Override to add @Nullable
391 @Override public abstract int compare(@Nullable T left, @Nullable T right);
392
393 /**
394 * Returns the {@code k} least elements of the given iterable according to
395 * this ordering, in order from least to greatest. If there are fewer than
396 * {@code k} elements present, all will be included.
397 *
398 * <p>The implementation does not necessarily use a <em>stable</em> sorting
399 * algorithm; when multiple elements are equivalent, it is undefined which
400 * will come first.
401 *
402 * @return an immutable {@code RandomAccess} list of the {@code k} least
403 * elements in ascending order
404 * @throws IllegalArgumentException if {@code k} is negative
405 * @since 8
406 */
407 @Beta
408 public <E extends T> List<E> leastOf(Iterable<E> iterable, int k) {
409 checkArgument(k >= 0, "%d is negative", k);
410
411 // values is not an E[], but we use it as such for readability. Hack.
412 @SuppressWarnings("unchecked")
413 E[] values = (E[]) Iterables.toArray(iterable);
414
415 // TODO(nshupe): also sort whole list if k is *near* values.length?
416 // TODO(kevinb): benchmark this impl against hand-coded heap
417 E[] resultArray;
418 if (values.length <= k) {
419 Arrays.sort(values, this);
420 resultArray = values;
421 } else {
422 quicksortLeastK(values, 0, values.length - 1, k);
423
424 // this is not an E[], but we use it as such for readability. Hack.
425 @SuppressWarnings("unchecked")
426 E[] tmp = (E[]) new Object[k];
427 resultArray = tmp;
428 System.arraycopy(values, 0, resultArray, 0, k);
429 }
430
431 return Collections.unmodifiableList(Arrays.asList(resultArray));
432 }
433
434 /**
435 * Returns the {@code k} greatest elements of the given iterable according to
436 * this ordering, in order from greatest to least. If there are fewer than
437 * {@code k} elements present, all will be included.
438 *
439 * <p>The implementation does not necessarily use a <em>stable</em> sorting
440 * algorithm; when multiple elements are equivalent, it is undefined which
441 * will come first.
442 *
443 * @return an immutable {@code RandomAccess} list of the {@code k} greatest
444 * elements in <i>descending order</i>
445 * @throws IllegalArgumentException if {@code k} is negative
446 * @since 8
447 */
448 @Beta
449 public <E extends T> List<E> greatestOf(Iterable<E> iterable, int k) {
450 // TODO(kevinb): see if delegation is hurting performance noticeably
451 // TODO(kevinb): if we change this implementation, add full unit tests.
452 return reverse().leastOf(iterable, k);
453 }
454
455 private <E extends T> void quicksortLeastK(
456 E[] values, int left, int right, int k) {
457 if (right > left) {
458 int pivotIndex = (left + right) >>> 1; // left + ((right - left) / 2)
459 int pivotNewIndex = partition(values, left, right, pivotIndex);
460 quicksortLeastK(values, left, pivotNewIndex - 1, k);
461 if (pivotNewIndex < k) {
462 quicksortLeastK(values, pivotNewIndex + 1, right, k);
463 }
464 }
465 }
466
467 private <E extends T> int partition(
468 E[] values, int left, int right, int pivotIndex) {
469 E pivotValue = values[pivotIndex];
470
471 values[pivotIndex] = values[right];
472 values[right] = pivotValue;
473
474 int storeIndex = left;
475 for (int i = left; i < right; i++) {
476 if (compare(values[i], pivotValue) < 0) {
477 ObjectArrays.swap(values, storeIndex, i);
478 storeIndex++;
479 }
480 }
481 ObjectArrays.swap(values, right, storeIndex);
482 return storeIndex;
483 }
484
485 /**
486 * {@link Collections#binarySearch(List, Object, Comparator) Searches}
487 * {@code sortedList} for {@code key} using the binary search algorithm. The
488 * list must be sorted using this ordering.
489 *
490 * @param sortedList the list to be searched
491 * @param key the key to be searched for
492 */
493 public int binarySearch(List<? extends T> sortedList, @Nullable T key) {
494 return Collections.binarySearch(sortedList, key, this);
495 }
496
497 /**
498 * Returns a copy of the given iterable sorted by this ordering. The input is
499 * not modified. The returned list is modifiable, serializable, and has random
500 * access.
501 *
502 * <p>Unlike {@link Sets#newTreeSet(Iterable)}, this method does not discard
503 * elements that are duplicates according to the comparator. The sort
504 * performed is <i>stable</i>, meaning that such elements will appear in the
505 * resulting list in the same order they appeared in the input.
506 *
507 * @param iterable the elements to be copied and sorted
508 * @return a new list containing the given elements in sorted order
509 */
510 public <E extends T> List<E> sortedCopy(Iterable<E> iterable) {
511 List<E> list = Lists.newArrayList(iterable);
512 Collections.sort(list, this);
513 return list;
514 }
515
516 /**
517 * Returns an <i>immutable</i> copy of the given iterable sorted by this
518 * ordering. The input is not modified.
519 *
520 * <p>Unlike {@link Sets#newTreeSet(Iterable)}, this method does not discard
521 * elements that are duplicates according to the comparator. The sort
522 * performed is <i>stable</i>, meaning that such elements will appear in the
523 * resulting list in the same order they appeared in the input.
524 *
525 * @param iterable the elements to be copied and sorted
526 * @return a new immutable list containing the given elements in sorted order
527 * @throws NullPointerException if {@code iterable} or any of its elements is
528 * null
529 * @since 3
530 */
531 public <E extends T> ImmutableList<E> immutableSortedCopy(
532 Iterable<E> iterable) {
533 return ImmutableList.copyOf(sortedCopy(iterable));
534 }
535
536 /**
537 * Returns {@code true} if each element in {@code iterable} after the first is
538 * greater than or equal to the element that preceded it, according to this
539 * ordering. Note that this is always true when the iterable has fewer than
540 * two elements.
541 */
542 public boolean isOrdered(Iterable<? extends T> iterable) {
543 Iterator<? extends T> it = iterable.iterator();
544 if (it.hasNext()) {
545 T prev = it.next();
546 while (it.hasNext()) {
547 T next = it.next();
548 if (compare(prev, next) > 0) {
549 return false;
550 }
551 prev = next;
552 }
553 }
554 return true;
555 }
556
557 /**
558 * Returns {@code true} if each element in {@code iterable} after the first is
559 * <i>strictly</i> greater than the element that preceded it, according to
560 * this ordering. Note that this is always true when the iterable has fewer
561 * than two elements.
562 */
563 public boolean isStrictlyOrdered(Iterable<? extends T> iterable) {
564 Iterator<? extends T> it = iterable.iterator();
565 if (it.hasNext()) {
566 T prev = it.next();
567 while (it.hasNext()) {
568 T next = it.next();
569 if (compare(prev, next) >= 0) {
570 return false;
571 }
572 prev = next;
573 }
574 }
575 return true;
576 }
577
578 /**
579 * Returns the greatest of the specified values according to this ordering. If
580 * there are multiple greatest values, the first of those is returned.
581 *
582 * @param iterable the iterable whose maximum element is to be determined
583 * @throws NoSuchElementException if {@code iterable} is empty
584 * @throws ClassCastException if the parameters are not <i>mutually
585 * comparable</i> under this ordering.
586 */
587 public <E extends T> E max(Iterable<E> iterable) {
588 Iterator<E> iterator = iterable.iterator();
589
590 // let this throw NoSuchElementException as necessary
591 E maxSoFar = iterator.next();
592
593 while (iterator.hasNext()) {
594 maxSoFar = max(maxSoFar, iterator.next());
595 }
596
597 return maxSoFar;
598 }
599
600 /**
601 * Returns the greatest of the specified values according to this ordering. If
602 * there are multiple greatest values, the first of those is returned.
603 *
604 * @param a value to compare, returned if greater than or equal to the rest.
605 * @param b value to compare
606 * @param c value to compare
607 * @param rest values to compare
608 * @throws ClassCastException if the parameters are not <i>mutually
609 * comparable</i> under this ordering.
610 */
611 public <E extends T> E max(
612 @Nullable E a, @Nullable E b, @Nullable E c, E... rest) {
613 E maxSoFar = max(max(a, b), c);
614
615 for (E r : rest) {
616 maxSoFar = max(maxSoFar, r);
617 }
618
619 return maxSoFar;
620 }
621
622 /**
623 * Returns the greater of the two values according to this ordering. If the
624 * values compare as 0, the first is returned.
625 *
626 * <p><b>Implementation note:</b> this method is invoked by the default
627 * implementations of the other {@code max} overloads, so overriding it will
628 * affect their behavior.
629 *
630 * @param a value to compare, returned if greater than or equal to b.
631 * @param b value to compare.
632 * @throws ClassCastException if the parameters are not <i>mutually
633 * comparable</i> under this ordering.
634 */
635 public <E extends T> E max(@Nullable E a, @Nullable E b) {
636 return compare(a, b) >= 0 ? a : b;
637 }
638
639 /**
640 * Returns the least of the specified values according to this ordering. If
641 * there are multiple least values, the first of those is returned.
642 *
643 * @param iterable the iterable whose minimum element is to be determined
644 * @throws NoSuchElementException if {@code iterable} is empty
645 * @throws ClassCastException if the parameters are not <i>mutually
646 * comparable</i> under this ordering.
647 */
648 public <E extends T> E min(Iterable<E> iterable) {
649 Iterator<E> iterator = iterable.iterator();
650
651 // let this throw NoSuchElementException as necessary
652 E minSoFar = iterator.next();
653
654 while (iterator.hasNext()) {
655 minSoFar = min(minSoFar, iterator.next());
656 }
657
658 return minSoFar;
659 }
660
661 /**
662 * Returns the least of the specified values according to this ordering. If
663 * there are multiple least values, the first of those is returned.
664 *
665 * @param a value to compare, returned if less than or equal to the rest.
666 * @param b value to compare
667 * @param c value to compare
668 * @param rest values to compare
669 * @throws ClassCastException if the parameters are not <i>mutually
670 * comparable</i> under this ordering.
671 */
672 public <E extends T> E min(
673 @Nullable E a, @Nullable E b, @Nullable E c, E... rest) {
674 E minSoFar = min(min(a, b), c);
675
676 for (E r : rest) {
677 minSoFar = min(minSoFar, r);
678 }
679
680 return minSoFar;
681 }
682
683 /**
684 * Returns the lesser of the two values according to this ordering. If the
685 * values compare as 0, the first is returned.
686 *
687 * <p><b>Implementation note:</b> this method is invoked by the default
688 * implementations of the other {@code min} overloads, so overriding it will
689 * affect their behavior.
690 *
691 * @param a value to compare, returned if less than or equal to b.
692 * @param b value to compare.
693 * @throws ClassCastException if the parameters are not <i>mutually
694 * comparable</i> under this ordering.
695 */
696 public <E extends T> E min(@Nullable E a, @Nullable E b) {
697 return compare(a, b) <= 0 ? a : b;
698 }
699
700 // Never make these public
701 static final int LEFT_IS_GREATER = 1;
702 static final int RIGHT_IS_GREATER = -1;
703 }