com.google.common.collect

Class Comparators

java.lang.Object

com.google.common.collect.Comparators

@Beta
 @GwtCompatible
public final class Comparators
extends Object

Provides static methods for working with Comparator instances. For many other helpful comparator utilities, see either Comparator itself (for Java 8 or later), or com.google.common.collect.Ordering (otherwise).

Relationship to Ordering

In light of the significant enhancements to Comparator in Java 8, the overwhelming majority of usages of Ordering can be written using only built-in JDK APIs. Because of this, and because it's awkward to have to convert comparators into Ordering instances, Ordering and its methods are planned for deletion. This class is intended to "fill the gap" and provide those features of Ordering not already provided by the JDK.

Since:

21.0

Author:

Louis Wasserman

Method Summary

Modifier and Type	Method and Description
static <T> boolean	isInOrder(Iterable<? extends T> iterable, Comparator<T> comparator) Returns true if each element in iterable after the first is greater than or equal to the element that preceded it, according to the specified comparator.
static <T> boolean	isInStrictOrder(Iterable<? extends T> iterable, Comparator<T> comparator) Returns true if each element in iterable after the first is strictly greater than the element that preceded it, according to the specified comparator.
static <T,S extends T> Comparator<Iterable<S>>	lexicographical(Comparator<T> comparator) 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.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

lexicographical

public static <T,S extends T> Comparator<Iterable<S>> lexicographical(Comparator<T> comparator)

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 [] < [1] < [1, 1] < [1, 2] < [2].

Note that Collections.reverseOrder(lexicographical(comparator)) is not equivalent to lexicographical(Collections.reverseOrder(comparator)) (consider how each would order [1] and [1, 1]).

isInOrder

public static <T> boolean isInOrder(Iterable<? extends T> iterable,
                                    Comparator<T> comparator)

Returns true if each element in 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.

isInStrictOrder

public static <T> boolean isInStrictOrder(Iterable<? extends T> iterable,
                                          Comparator<T> comparator)

Returns true if each element in iterable after the first is strictly 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.