| /* |
| * Copyright (C) 2016 The Guava Authors |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.google.common.collect; |
| |
| import static com.google.common.base.Preconditions.checkNotNull; |
| |
| import com.google.common.annotations.Beta; |
| import com.google.common.annotations.GwtCompatible; |
| import java.util.Comparator; |
| import java.util.Iterator; |
| import org.checkerframework.checker.nullness.qual.Nullable; |
| |
| /** |
| * Provides static methods for working with {@link Comparator} instances. For many other helpful |
| * comparator utilities, see either {@code Comparator} itself (for Java 8 or later), or {@code |
| * com.google.common.collect.Ordering} (otherwise). |
| * |
| * <h3>Relationship to {@code Ordering}</h3> |
| * |
| * <p>In light of the significant enhancements to {@code Comparator} in Java 8, the overwhelming |
| * majority of usages of {@code Ordering} can be written using only built-in JDK APIs. This class is |
| * intended to "fill the gap" and provide those features of {@code Ordering} not already provided by |
| * the JDK. |
| * |
| * @since 21.0 |
| * @author Louis Wasserman |
| */ |
| @Beta |
| @GwtCompatible |
| @ElementTypesAreNonnullByDefault |
| public final class Comparators { |
| private Comparators() {} |
| |
| /** |
| * Returns a new comparator which sorts iterables by comparing corresponding elements pairwise |
| * until a nonzero result is found; imposes "dictionary order." If the end of one iterable is |
| * reached, but not the other, the shorter iterable is considered to be less than the longer one. |
| * For example, a lexicographical natural ordering over integers considers {@code [] < [1] < [1, |
| * 1] < [1, 2] < [2]}. |
| * |
| * <p>Note that {@code Collections.reverseOrder(lexicographical(comparator))} is not equivalent to |
| * {@code lexicographical(Collections.reverseOrder(comparator))} (consider how each would order |
| * {@code [1]} and {@code [1, 1]}). |
| */ |
| // Note: 90% of the time we don't add type parameters or wildcards that serve only to "tweak" the |
| // desired return type. However, *nested* generics introduce a special class of problems that we |
| // think tip it over into being worthwhile. |
| public static <T extends @Nullable Object, S extends T> Comparator<Iterable<S>> lexicographical( |
| Comparator<T> comparator) { |
| return new LexicographicalOrdering<S>(checkNotNull(comparator)); |
| } |
| |
| /** |
| * Returns {@code true} if each element in {@code iterable} after the first is greater than or |
| * equal to the element that preceded it, according to the specified comparator. Note that this is |
| * always true when the iterable has fewer than two elements. |
| */ |
| public static <T extends @Nullable Object> boolean isInOrder( |
| Iterable<? extends T> iterable, Comparator<T> comparator) { |
| checkNotNull(comparator); |
| Iterator<? extends T> it = iterable.iterator(); |
| if (it.hasNext()) { |
| T prev = it.next(); |
| while (it.hasNext()) { |
| T next = it.next(); |
| if (comparator.compare(prev, next) > 0) { |
| return false; |
| } |
| prev = next; |
| } |
| } |
| return true; |
| } |
| |
| /** |
| * Returns {@code true} if each element in {@code iterable} after the first is <i>strictly</i> |
| * greater than the element that preceded it, according to the specified comparator. Note that |
| * this is always true when the iterable has fewer than two elements. |
| */ |
| public static <T extends @Nullable Object> boolean isInStrictOrder( |
| Iterable<? extends T> iterable, Comparator<T> comparator) { |
| checkNotNull(comparator); |
| Iterator<? extends T> it = iterable.iterator(); |
| if (it.hasNext()) { |
| T prev = it.next(); |
| while (it.hasNext()) { |
| T next = it.next(); |
| if (comparator.compare(prev, next) >= 0) { |
| return false; |
| } |
| prev = next; |
| } |
| } |
| return true; |
| } |
| |
| /** |
| * Returns the minimum of the two values. If the values compare as 0, the first is returned. |
| * |
| * <p>The recommended solution for finding the {@code minimum} of some values depends on the type |
| * of your data and the number of elements you have. Read more in the Guava User Guide article on |
| * <a href="https://github.com/google/guava/wiki/CollectionUtilitiesExplained#comparators">{@code |
| * Comparators}</a>. |
| * |
| * @param a first value to compare, returned if less than or equal to b. |
| * @param b second value to compare. |
| * @throws ClassCastException if the parameters are not <i>mutually comparable</i>. |
| * @since 30.0 |
| */ |
| @Beta |
| public static <T extends Comparable<? super T>> T min(T a, T b) { |
| return (a.compareTo(b) <= 0) ? a : b; |
| } |
| |
| /** |
| * Returns the minimum of the two values, according to the given comparator. If the values compare |
| * as equal, the first is returned. |
| * |
| * <p>The recommended solution for finding the {@code minimum} of some values depends on the type |
| * of your data and the number of elements you have. Read more in the Guava User Guide article on |
| * <a href="https://github.com/google/guava/wiki/CollectionUtilitiesExplained#comparators">{@code |
| * Comparators}</a>. |
| * |
| * @param a first value to compare, returned if less than or equal to b |
| * @param b second value to compare. |
| * @throws ClassCastException if the parameters are not <i>mutually comparable</i> using the given |
| * comparator. |
| * @since 30.0 |
| */ |
| @Beta |
| @ParametricNullness |
| public static <T extends @Nullable Object> T min( |
| @ParametricNullness T a, @ParametricNullness T b, Comparator<T> comparator) { |
| return (comparator.compare(a, b) <= 0) ? a : b; |
| } |
| |
| /** |
| * Returns the maximum of the two values. If the values compare as 0, the first is returned. |
| * |
| * <p>The recommended solution for finding the {@code maximum} of some values depends on the type |
| * of your data and the number of elements you have. Read more in the Guava User Guide article on |
| * <a href="https://github.com/google/guava/wiki/CollectionUtilitiesExplained#comparators">{@code |
| * Comparators}</a>. |
| * |
| * @param a first value to compare, returned if greater than or equal to b. |
| * @param b second value to compare. |
| * @throws ClassCastException if the parameters are not <i>mutually comparable</i>. |
| * @since 30.0 |
| */ |
| @Beta |
| public static <T extends Comparable<? super T>> T max(T a, T b) { |
| return (a.compareTo(b) >= 0) ? a : b; |
| } |
| |
| /** |
| * Returns the maximum of the two values, according to the given comparator. If the values compare |
| * as equal, the first is returned. |
| * |
| * <p>The recommended solution for finding the {@code maximum} of some values depends on the type |
| * of your data and the number of elements you have. Read more in the Guava User Guide article on |
| * <a href="https://github.com/google/guava/wiki/CollectionUtilitiesExplained#comparators">{@code |
| * Comparators}</a>. |
| * |
| * @param a first value to compare, returned if greater than or equal to b. |
| * @param b second value to compare. |
| * @throws ClassCastException if the parameters are not <i>mutually comparable</i> using the given |
| * comparator. |
| * @since 30.0 |
| */ |
| @Beta |
| @ParametricNullness |
| public static <T extends @Nullable Object> T max( |
| @ParametricNullness T a, @ParametricNullness T b, Comparator<T> comparator) { |
| return (comparator.compare(a, b) >= 0) ? a : b; |
| } |
| } |