@GwtCompatible public final class Comparators extends Object
Comparator
instances. For many other helpful
comparator utilities, see either Comparator
itself (for Java 8 or later), or com.google.common.collect.Ordering
(otherwise).
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. This class is
intended to "fill the gap" and provide those features of Ordering
not already provided by
the JDK.
Modifier and Type | Method and Description |
---|---|
static <T> Comparator<Optional<T>> |
emptiesFirst(Comparator<? super T> valueComparator)
Returns a comparator of
Optional values which treats Optional.empty() as less
than all other values, and orders the rest using valueComparator on the contained
value. |
static <T> Comparator<Optional<T>> |
emptiesLast(Comparator<? super T> valueComparator)
Returns a comparator of
Optional values which treats Optional.empty() as greater
than all other values, and orders the rest using valueComparator on the contained
value. |
static <T> Collector<T,?,List<T>> |
greatest(int k,
Comparator<? super T> comparator)
Returns a
Collector that returns the k greatest (relative to the specified
Comparator ) input elements, in descending order, as an unmodifiable List . |
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> Collector<T,?,List<T>> |
least(int k,
Comparator<? super T> comparator)
Returns a
Collector that returns the k smallest (relative to the specified
Comparator ) input elements, in ascending order, as an unmodifiable List . |
static <T,S extends T> |
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.
|
@Beta public static <T,S extends T> Comparator<Iterable<S>> lexicographical(Comparator<T> comparator)
[] < [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]
).
@Beta public static <T> boolean isInOrder(Iterable<? extends T> iterable, Comparator<T> comparator)
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.@Beta public static <T> boolean isInStrictOrder(Iterable<? extends T> iterable, Comparator<T> comparator)
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.public static <T> Collector<T,?,List<T>> least(int k, Comparator<? super T> comparator)
Collector
that returns the k
smallest (relative to the specified
Comparator
) input elements, in ascending order, as an unmodifiable List
. Ties
are broken arbitrarily.
For example:
Stream.of("foo", "quux", "banana", "elephant")
.collect(least(2, comparingInt(String::length)))
// returns {"foo", "quux"}
This Collector
uses O(k) memory and takes expected time O(n) (worst-case O(n log
k)), as opposed to e.g. Stream.sorted(comparator).limit(k)
, which currently takes O(n
log n) time and O(n) space.
IllegalArgumentException
- if k < 0
public static <T> Collector<T,?,List<T>> greatest(int k, Comparator<? super T> comparator)
Collector
that returns the k
greatest (relative to the specified
Comparator
) input elements, in descending order, as an unmodifiable List
. Ties
are broken arbitrarily.
For example:
Stream.of("foo", "quux", "banana", "elephant")
.collect(greatest(2, comparingInt(String::length)))
// returns {"elephant", "banana"}
This Collector
uses O(k) memory and takes expected time O(n) (worst-case O(n log
k)), as opposed to e.g. Stream.sorted(comparator.reversed()).limit(k)
, which currently
takes O(n log n) time and O(n) space.
IllegalArgumentException
- if k < 0
@Beta public static <T> Comparator<Optional<T>> emptiesFirst(Comparator<? super T> valueComparator)
Optional
values which treats Optional.empty()
as less
than all other values, and orders the rest using valueComparator
on the contained
value.@Beta public static <T> Comparator<Optional<T>> emptiesLast(Comparator<? super T> valueComparator)
Optional
values which treats Optional.empty()
as greater
than all other values, and orders the rest using valueComparator
on the contained
value.Copyright © 2010–2019. All rights reserved.