Package com.tangosol.util.function

Interface Remote.Comparator<T>

Type Parameters:

T - the type of objects that may be compared by this comparator

All Superinterfaces:

Comparator<T>, Serializable

All Known Implementing Classes:

EntryComparator, InverseComparator, SafeComparator

Enclosing class:

Remote

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public static interface Remote.Comparator<T>
extends Comparator<T>, Serializable

A comparison function, which imposes a total ordering on some collection of objects. Comparators can be passed to a sort method (such as Collections.sort or Arrays.sort) to allow precise control over the sort order. Comparators can also be used to control the order of certain data structures (such as sorted sets or sorted maps), or to provide an ordering for collections of objects that don't have a natural ordering.

The ordering imposed by a comparator c on a set of elements S is said to be consistent with equals if and only if c.compare(e1, e2)==0 has the same boolean value as e1.equals(e2) for every e1 and e2 in S.

Caution should be exercised when using a comparator capable of imposing an ordering inconsistent with equals to order a sorted set (or sorted map). Suppose a sorted set (or sorted map) with an explicit comparator c is used with elements (or keys) drawn from a set S. If the ordering imposed by c on S is inconsistent with equals, the sorted set (or sorted map) will behave "strangely." In particular the sorted set (or sorted map) will violate the general contract for set (or map), which is defined in terms of equals.

For example, suppose one adds two elements a and b such that (a.equals(b) && c.compare(a, b) != 0) to an empty TreeSet with comparator c. The second add operation will return true (and the size of the tree set will increase) because a and b are not equivalent from the tree set's perspective, even though this is contrary to the specification of the Set.add method.

Note: It is generally a good idea for comparators to also implement java.io.Serializable, as they may be used as ordering methods in serializable data structures (like TreeSet, TreeMap). In order for the data structure to serialize successfully, the comparator (if provided) must implement Serializable.

For the mathematically inclined, the relation that defines the imposed ordering that a given comparator c imposes on a given set of objects S is:

       {(x, y) such that c.compare(x, y) <= 0}.
 

The quotient for this total order is:

       {(x, y) such that c.compare(x, y) == 0}.
 

It follows immediately from the contract for compare that the quotient is an equivalence relation on S, and that the imposed ordering is a total order on S. When we say that the ordering imposed by c on S is consistent with equals, we mean that the quotient for the ordering is the equivalence relation defined by the objects' equals(Object) method(s):

     {(x, y) such that x.equals(y)}. 

Unlike Comparable, a comparator may optionally permit comparison of null arguments, while maintaining the requirements for an equivalence relation.

This interface is a member of the Java Collections Framework.

Method Summary

Modifier and Type	Method	Description
static <T,U extends Comparable<? super U>> Remote.Comparator<T>	comparing(Remote.Function<? super T,? extends U> keyExtractor)	Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator<T> that compares by that sort key.
static <T,U> Remote.Comparator<T>	comparing(Remote.Function<? super T,? extends U> keyExtractor, Remote.Comparator<? super U> keyComparator)	Accepts a function that extracts a sort key from a type T, and returns a Comparator<T> that compares by that sort key using the specified Remote.Comparator.
static <T> Remote.Comparator<T>	comparingDouble(Remote.ToDoubleFunction<? super T> keyExtractor)	Accepts a function that extracts a double sort key from a type T, and returns a Comparator<T> that compares by that sort key.
static <T> Remote.Comparator<T>	comparingInt(Remote.ToIntFunction<? super T> keyExtractor)	Accepts a function that extracts an int sort key from a type T, and returns a Comparator<T> that compares by that sort key.
static <T> Remote.Comparator<T>	comparingLong(Remote.ToLongFunction<? super T> keyExtractor)	Accepts a function that extracts a long sort key from a type T, and returns a Comparator<T> that compares by that sort key.
static <T extends Comparable<? super T>> Remote.Comparator<T>	naturalOrder()	Returns a comparator that compares Comparable objects in natural order.
static <T> Remote.Comparator<T>	nullsFirst(Remote.Comparator<T> comparator)	Returns a null-friendly comparator that considers null to be less than non-null.
static <T> Remote.Comparator<T>	nullsLast(Remote.Comparator<T> comparator)	Returns a null-friendly comparator that considers null to be greater than non-null.
default Remote.Comparator<T>	reversed()	Returns a comparator that imposes the reverse ordering of this comparator.
static <T extends Comparable<? super T>> Remote.Comparator<T>	reverseOrder()	Returns a comparator that imposes the reverse of the natural ordering.
default Remote.Comparator<T>	thenComparing(Remote.Comparator<? super T> other)	Returns a lexicographic-order comparator with another comparator.
default <U extends Comparable<? super U>> Remote.Comparator<T>	thenComparing(Remote.Function<? super T,? extends U> keyExtractor)	Returns a lexicographic-order comparator with a function that extracts a Comparable sort key.
default <U> Remote.Comparator<T>	thenComparing(Remote.Function<? super T,? extends U> keyExtractor, Remote.Comparator<? super U> keyComparator)	Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator.
default Remote.Comparator<T>	thenComparingDouble(Remote.ToDoubleFunction<? super T> keyExtractor)	Returns a lexicographic-order comparator with a function that extracts a double sort key.
default Remote.Comparator<T>	thenComparingInt(Remote.ToIntFunction<? super T> keyExtractor)	Returns a lexicographic-order comparator with a function that extracts a int sort key.
default Remote.Comparator<T>	thenComparingLong(Remote.ToLongFunction<? super T> keyExtractor)	Returns a lexicographic-order comparator with a function that extracts a long sort key.

Methods inherited from interface java.util.Comparator

compare, equals, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong

Method Detail

reversed

default Remote.Comparator<T> reversed()

Returns a comparator that imposes the reverse ordering of this comparator.

Specified by:

reversed in interface Comparator<T>

Returns:

a comparator that imposes the reverse ordering of this comparator.

thenComparing

default Remote.Comparator<T> thenComparing(Remote.Comparator<? super T> other)

Returns a lexicographic-order comparator with another comparator. If this Comparator considers two elements equal, i.e. compare(a, b) == 0, other is used to determine the order.

Parameters:

other - the other comparator to be used when this comparator compares two objects that are equal.

Returns:

a lexicographic-order comparator composed of this and then the other comparator

Throws:

NullPointerException - if the argument is null.

Since:

1.8

API Note:

For example, to sort a collection of String based on the length and then case-insensitive natural ordering, the comparator can be composed using following code,

     Comparator<String> cmp = Comparator.comparingInt(String::length)
             .thenComparing(String.CASE_INSENSITIVE_ORDER);
 

thenComparing

default <U> Remote.Comparator<T> thenComparing(Remote.Function<? super T,? extends U> keyExtractor,
                                               Remote.Comparator<? super U> keyComparator)

Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given Comparator.

Type Parameters:

U - the type of the sort key

Parameters:

keyExtractor - the function used to extract the sort key

keyComparator - the Comparator used to compare the sort key

Returns:

a lexicographic-order comparator composed of this comparator and then comparing on the key extracted by the keyExtractor function

Throws:

NullPointerException - if either argument is null.

See Also:

comparing(Function, Comparator), thenComparing(Comparator)

Implementation Requirements:

This default implementation behaves as if thenComparing(comparing(keyExtractor, cmp)) .

thenComparing

default <U extends Comparable<? super U>> Remote.Comparator<T> thenComparing(Remote.Function<? super T,? extends U> keyExtractor)

Returns a lexicographic-order comparator with a function that extracts a Comparable sort key.

Type Parameters:

U - the type of the Comparable sort key

Parameters:

keyExtractor - the function used to extract the Comparable sort key

Returns:

a lexicographic-order comparator composed of this and then the Comparable sort key.

Throws:

NullPointerException - if the argument is null.

See Also:

comparing(Function), thenComparing(Comparator)

Implementation Requirements:

This default implementation behaves as if thenComparing(comparing(keyExtractor)).

thenComparingInt

default Remote.Comparator<T> thenComparingInt(Remote.ToIntFunction<? super T> keyExtractor)

Returns a lexicographic-order comparator with a function that extracts a int sort key.

Parameters:

keyExtractor - the function used to extract the integer sort key

Returns:

a lexicographic-order comparator composed of this and then the int sort key

Throws:

NullPointerException - if the argument is null.

See Also:

comparingInt(ToIntFunction), thenComparing(Comparator)

Implementation Requirements:

This default implementation behaves as if thenComparing(comparingInt(keyExtractor)).

thenComparingLong

default Remote.Comparator<T> thenComparingLong(Remote.ToLongFunction<? super T> keyExtractor)

Returns a lexicographic-order comparator with a function that extracts a long sort key.

Parameters:

keyExtractor - the function used to extract the long sort key

Returns:

a lexicographic-order comparator composed of this and then the long sort key

Throws:

NullPointerException - if the argument is null.

See Also:

comparingLong(ToLongFunction), thenComparing(Comparator)

Implementation Requirements:

This default implementation behaves as if thenComparing(comparingLong(keyExtractor)).

thenComparingDouble

default Remote.Comparator<T> thenComparingDouble(Remote.ToDoubleFunction<? super T> keyExtractor)

Returns a lexicographic-order comparator with a function that extracts a double sort key.

Parameters:

keyExtractor - the function used to extract the double sort key

Returns:

a lexicographic-order comparator composed of this and then the double sort key

Throws:

NullPointerException - if the argument is null.

See Also:

comparingDouble(ToDoubleFunction), thenComparing(Comparator)

Implementation Requirements:

This default implementation behaves as if thenComparing(comparingDouble(keyExtractor)).

reverseOrder

static <T extends Comparable<? super T>> Remote.Comparator<T> reverseOrder()

Returns a comparator that imposes the reverse of the natural ordering.

Type Parameters:

T - the Comparable type of element to be compared

Returns:

a comparator that imposes the reverse of the natural ordering on Comparable objects.

See Also:

Comparable

naturalOrder

static <T extends Comparable<? super T>> Remote.Comparator<T> naturalOrder()

Returns a comparator that compares Comparable objects in natural order.

Type Parameters:

T - the Comparable type of element to be compared

Returns:

a comparator that imposes the natural ordering on Comparable objects.

Since:

1.8

See Also:

Comparable

nullsFirst

static <T> Remote.Comparator<T> nullsFirst(Remote.Comparator<T> comparator)

Returns a null-friendly comparator that considers null to be less than non-null. When both are null, they are considered equal. If both are non-null, the specified Comparator is used to determine the order. If the specified comparator is null, then the returned comparator considers all non-null values to be equal.

Type Parameters:

T - the type of the elements to be compared

Parameters:

comparator - a Comparator for comparing non-null values

Returns:

a comparator that considers null to be less than non-null, and compares non-null objects with the supplied Comparator.

nullsLast

static <T> Remote.Comparator<T> nullsLast(Remote.Comparator<T> comparator)

Returns a null-friendly comparator that considers null to be greater than non-null. When both are null, they are considered equal. If both are non-null, the specified Comparator is used to determine the order. If the specified comparator is null, then the returned comparator considers all non-null values to be equal.

Type Parameters:

T - the type of the elements to be compared

Parameters:

comparator - a Comparator for comparing non-null values

Returns:

a comparator that considers null to be greater than non-null, and compares non-null objects with the supplied Comparator.

comparing

static <T,U> Remote.Comparator<T> comparing(Remote.Function<? super T,? extends U> keyExtractor,
                                                  Remote.Comparator<? super U> keyComparator)

Accepts a function that extracts a sort key from a type T, and returns a Comparator<T> that compares by that sort key using the specified Remote.Comparator.

Type Parameters:

T - the type of element to be compared

U - the type of the sort key

Parameters:

keyExtractor - the function used to extract the sort key

keyComparator - the Comparator used to compare the sort key

Returns:

a comparator that compares by an extracted key using the specified Comparator

Throws:

NullPointerException - if either argument is null

API Note:

For example, to obtain a Comparator that compares Person objects by their last name ignoring case differences,

     Comparator<Person> cmp = Comparator.comparing(
             Person::getLastName,
             String.CASE_INSENSITIVE_ORDER);
 

comparing

static <T,U extends Comparable<? super U>> Remote.Comparator<T> comparing(Remote.Function<? super T,? extends U> keyExtractor)

Accepts a function that extracts a Comparable sort key from a type T, and returns a Comparator<T> that compares by that sort key.

Type Parameters:

T - the type of element to be compared

U - the type of the Comparable sort key

Parameters:

keyExtractor - the function used to extract the Comparable sort key

Returns:

a comparator that compares by an extracted key

Throws:

NullPointerException - if the argument is null

API Note:

For example, to obtain a Comparator that compares Person objects by their last name,

     Comparator<Person> byLastName = Comparator.comparing(Person::getLastName);
 

comparingInt

static <T> Remote.Comparator<T> comparingInt(Remote.ToIntFunction<? super T> keyExtractor)

Accepts a function that extracts an int sort key from a type T, and returns a Comparator<T> that compares by that sort key.

Type Parameters:

T - the type of element to be compared

Parameters:

keyExtractor - the function used to extract the integer sort key

Returns:

a comparator that compares by an extracted key

Throws:

NullPointerException - if the argument is null

See Also:

comparing(Function)

comparingLong

static <T> Remote.Comparator<T> comparingLong(Remote.ToLongFunction<? super T> keyExtractor)

Accepts a function that extracts a long sort key from a type T, and returns a Comparator<T> that compares by that sort key.

Type Parameters:

T - the type of element to be compared

Parameters:

keyExtractor - the function used to extract the long sort key

Returns:

a comparator that compares by an extracted key

Throws:

NullPointerException - if the argument is null

See Also:

comparing(Function)

comparingDouble

static <T> Remote.Comparator<T> comparingDouble(Remote.ToDoubleFunction<? super T> keyExtractor)

Accepts a function that extracts a double sort key from a type T, and returns a Comparator<T> that compares by that sort key.

Type Parameters:

T - the type of element to be compared

Parameters:

keyExtractor - the function used to extract the double sort key

Returns:

a comparator that compares by an extracted key

Throws:

NullPointerException - if the argument is null

See Also:

comparing(Function)