OpenJDK 1.23 · java.util.Comparator · APIdia, the JavaDoc alternative

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)}.

In other words, when the imposed ordering is consistent with equals, the equivalence classes defined by the equivalence relation of the equals method and the equivalence classes defined by the quotient of the compare method are the same.

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 and Description
public int	Returns: a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. compare(T the first object to be compared. o1, T the second object to be compared. o2) Compares its two arguments for order.
public static < the type of element to be compared T, the type of the sort key U> Comparator<T>	Returns: a comparator that compares by an extracted key using the specified `Comparator` comparing(Function<? super T, ? extends U> the function used to extract the sort key keyExtractor, Comparator<? super U> the `Comparator` used to compare the sort key 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 `Comparator`.
public static < the type of element to be compared T, the type of the `Comparable` sort key U extends Comparable<? super U>> Comparator<T>	Returns: a comparator that compares by an extracted key comparing(Function<? super T, ? extends U> the function used to extract the `Comparable` sort key 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.
public static < the type of element to be compared T> Comparator<T>	Returns: a comparator that compares by an extracted key comparingDouble(ToDoubleFunction<? super T> the function used to extract the double sort key 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.
public static < the type of element to be compared T> Comparator<T>	Returns: a comparator that compares by an extracted key comparingInt(ToIntFunction<? super T> the function used to extract the integer sort key 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.
public static < the type of element to be compared T> Comparator<T>	Returns: a comparator that compares by an extracted key comparingLong(ToLongFunction<? super T> the function used to extract the long sort key 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.
public boolean	Returns: `true` only if the specified object is also a comparator and it imposes the same ordering as this comparator. equals(Object the reference object with which to compare. obj) Indicates whether some other object is "equal to" this comparator.
public static < the `Comparable` type of element to be compared T extends Comparable<? super T>> Comparator<T>	Returns: a comparator that imposes the natural ordering on `Comparable` objects. naturalOrder() Returns a comparator that compares `Comparable` objects in natural order.
public static < the type of the elements to be compared T> Comparator<T>	Returns: a comparator that considers `null` to be less than non-null, and compares non-null objects with the supplied `Comparator`. nullsFirst(Comparator<? super T> a `Comparator` for comparing non-null values comparator) Returns a null-friendly comparator that considers `null` to be less than non-null.
public static < the type of the elements to be compared T> Comparator<T>	Returns: a comparator that considers `null` to be greater than non-null, and compares non-null objects with the supplied `Comparator`. nullsLast(Comparator<? super T> a `Comparator` for comparing non-null values comparator) Returns a null-friendly comparator that considers `null` to be greater than non-null.
public default Comparator<T>	Returns: a comparator that imposes the reverse ordering of this comparator. reversed() Returns a comparator that imposes the reverse ordering of this comparator.
public static < the `Comparable` type of element to be compared T extends Comparable<? super T>> Comparator<T>	Returns: a comparator that imposes the reverse of the natural ordering on `Comparable` objects. reverseOrder() Returns a comparator that imposes the reverse of the natural ordering.
public default Comparator<T>	Returns: a lexicographic-order comparator composed of this and then the other comparator thenComparing(Comparator<? super T> the other comparator to be used when this comparator compares two objects that are equal. other) Returns a lexicographic-order comparator with another comparator.
public default < the type of the sort key U> Comparator<T>	Returns: a lexicographic-order comparator composed of this comparator and then comparing on the key extracted by the keyExtractor function thenComparing(Function<? super T, ? extends U> the function used to extract the sort key keyExtractor, Comparator<? super U> the `Comparator` used to compare the sort key keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given `Comparator`.
public default < the type of the `Comparable` sort key U extends Comparable<? super U>> Comparator<T>	Returns: a lexicographic-order comparator composed of this and then the `Comparable` sort key. thenComparing(Function<? super T, ? extends U> the function used to extract the `Comparable` sort key keyExtractor) Returns a lexicographic-order comparator with a function that extracts a `Comparable` sort key.
public default Comparator<T>	Returns: a lexicographic-order comparator composed of this and then the `double` sort key thenComparingDouble(ToDoubleFunction<? super T> the function used to extract the double sort key keyExtractor) Returns a lexicographic-order comparator with a function that extracts a `double` sort key.
public default Comparator<T>	Returns: a lexicographic-order comparator composed of this and then the `int` sort key thenComparingInt(ToIntFunction<? super T> the function used to extract the integer sort key keyExtractor) Returns a lexicographic-order comparator with a function that extracts an `int` sort key.
public default Comparator<T>	Returns: a lexicographic-order comparator composed of this and then the `long` sort key thenComparingLong(ToLongFunction<? super T> the function used to extract the long sort key keyExtractor) Returns a lexicographic-order comparator with a function that extracts a `long` sort key.

Method Detail

compare back to summary

compare	back to summary
public int compare(T o1, T o2) Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. The implementor must ensure that `signum(compare(x, y)) == -signum(compare(y, x))` for all `x` and `y`. (This implies that `compare(x, y)` must throw an exception if and only if `compare(y, x)` throws an exception.) The implementor must also ensure that the relation is transitive: `((compare(x, y)>0) && (compare(y, z)>0))` implies `compare(x, z)>0`. Finally, the implementor must ensure that `compare(x, y)==0` implies that `signum(compare(x, z))==signum(compare(y, z))` for all `z`. API Note It is generally the case, but not strictly required that `(compare(x, y)==0) == (x.equals(y))`. Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals." Parameters o1:T the first object to be compared. o2:T the second object to be compared. Returns:int a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second. Exceptions NullPointerException: if an argument is null and this comparator does not permit null arguments ClassCastException: if the arguments' types prevent them from being compared by this comparator.

public int compare(T o1, T o2)

Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.

The implementor must ensure that signum(compare(x, y)) == -signum(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.)

The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0.

Finally, the implementor must ensure that compare(x, y)==0 implies that signum(compare(x, z))==signum(compare(y, z)) for all z.

API Note

It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals."

Parameters

o1:T: the first object to be compared.
o2:T: the second object to be compared.

Returns:int

a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.

Exceptions

NullPointerException:: if an argument is null and this comparator does not permit null arguments
ClassCastException:: if the arguments' types prevent them from being compared by this comparator.

comparing back to summary

comparing	back to summary
public static <T, U> Comparator<T> comparing(Function<? super T, ? extends U> keyExtractor, 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 `Comparator`. The returned comparator is serializable if the specified function and comparator are both serializable. 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);` Parameters <T> the type of element to be compared <U> the type of the sort key keyExtractor:Function<? super T, ? extends U> the function used to extract the sort key keyComparator:Comparator<? super U> the `Comparator` used to compare the sort key Returns:Comparator<T> a comparator that compares by an extracted key using the specified `Comparator` Exceptions NullPointerException: if either argument is null Since 1.8

public static <T, U> Comparator<T> comparing(Function<? super T, ? extends U> keyExtractor, 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 Comparator.

The returned comparator is serializable if the specified function and comparator are both serializable.

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);

Parameters

<T>: the type of element to be compared
: the type of the sort key
keyExtractor:Function<? super T, ? extends U>: the function used to extract the sort key
keyComparator:Comparator<? super U>: the Comparator used to compare the sort key

Returns:Comparator<T>

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

Exceptions

NullPointerException:: if either argument is null

Since

1.8

comparing back to summary

comparing	back to summary
public static <T, U extends Comparable<? super U>> Comparator<T> comparing(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. The returned comparator is serializable if the specified function is also serializable. API Note For example, to obtain a `Comparator` that compares `Person` objects by their last name, `Comparator<Person> byLastName = Comparator.comparing(Person::getLastName);` Parameters <T> the type of element to be compared <U> the type of the `Comparable` sort key keyExtractor:Function<? super T, ? extends U> the function used to extract the `Comparable` sort key Returns:Comparator<T> a comparator that compares by an extracted key Exceptions NullPointerException: if the argument is null Since 1.8

public static <T, U extends Comparable<? super U>> Comparator<T> comparing(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.

The returned comparator is serializable if the specified function is also serializable.

API Note

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

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

Parameters

<T>: the type of element to be compared
: the type of the Comparable sort key
keyExtractor:Function<? super T, ? extends U>: the function used to extract the Comparable sort key

Returns:Comparator<T>

a comparator that compares by an extracted key

Exceptions

NullPointerException:: if the argument is null

Since

1.8

comparingDouble back to summary

comparingDouble	back to summary
public static <T> Comparator<T> comparingDouble(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. The returned comparator is serializable if the specified function is also serializable. Parameters <T> the type of element to be compared keyExtractor:ToDoubleFunction<? super T> the function used to extract the double sort key Returns:Comparator<T> a comparator that compares by an extracted key Exceptions NullPointerException: if the argument is null Since 1.8 See Also `comparing(Function)`

public static <T> Comparator<T> comparingDouble(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.

The returned comparator is serializable if the specified function is also serializable.

Parameters

<T>: the type of element to be compared
keyExtractor:ToDoubleFunction<? super T>: the function used to extract the double sort key

Returns:Comparator<T>

a comparator that compares by an extracted key

Exceptions

NullPointerException:: if the argument is null

Since

1.8

See Also

comparing(Function)

comparingInt back to summary

comparingInt	back to summary
public static <T> Comparator<T> comparingInt(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. The returned comparator is serializable if the specified function is also serializable. Parameters <T> the type of element to be compared keyExtractor:ToIntFunction<? super T> the function used to extract the integer sort key Returns:Comparator<T> a comparator that compares by an extracted key Exceptions NullPointerException: if the argument is null Since 1.8 See Also `comparing(Function)`

public static <T> Comparator<T> comparingInt(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.

The returned comparator is serializable if the specified function is also serializable.

Parameters

<T>: the type of element to be compared
keyExtractor:ToIntFunction<? super T>: the function used to extract the integer sort key

Returns:Comparator<T>

a comparator that compares by an extracted key

Exceptions

NullPointerException:: if the argument is null

Since

1.8

See Also

comparing(Function)

comparingLong back to summary

comparingLong	back to summary
public static <T> Comparator<T> comparingLong(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. The returned comparator is serializable if the specified function is also serializable. Parameters <T> the type of element to be compared keyExtractor:ToLongFunction<? super T> the function used to extract the long sort key Returns:Comparator<T> a comparator that compares by an extracted key Exceptions NullPointerException: if the argument is null Since 1.8 See Also `comparing(Function)`

public static <T> Comparator<T> comparingLong(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.

The returned comparator is serializable if the specified function is also serializable.

Parameters

<T>: the type of element to be compared
keyExtractor:ToLongFunction<? super T>: the function used to extract the long sort key

Returns:Comparator<T>

a comparator that compares by an extracted key

Exceptions

NullPointerException:: if the argument is null

Since

1.8

See Also

comparing(Function)

equals back to summary

equals	back to summary
public boolean equals(Object obj) Indicates whether some other object is "equal to" this comparator. This method must obey the general contract of `Object#equals(Object)`. Additionally, this method can return `true` only if the specified object is also a comparator and it imposes the same ordering as this comparator. Thus, `comp1.equals(comp2)` implies that `signum(comp1.compare(o1, o2))==signum(comp2.compare(o1, o2))` for every object reference `o1` and `o2`. Note that it is always safe not to override `Object.equals(Object)`. However, overriding this method may, in some cases, improve performance by allowing programs to determine that two distinct comparators impose the same order. Parameters obj:Object the reference object with which to compare. Returns:boolean `true` only if the specified object is also a comparator and it imposes the same ordering as this comparator. See Also `Object#equals(Object)`, `Object#hashCode()`

public boolean equals(Object obj)

Indicates whether some other object is "equal to" this comparator. This method must obey the general contract of Object#equals(Object). Additionally, this method can return true only if the specified object is also a comparator and it imposes the same ordering as this comparator. Thus, comp1.equals(comp2) implies that signum(comp1.compare(o1, o2))==signum(comp2.compare(o1, o2)) for every object reference o1 and o2.

Note that it is always safe not to override Object.equals(Object). However, overriding this method may, in some cases, improve performance by allowing programs to determine that two distinct comparators impose the same order.

Parameters

obj:Object: the reference object with which to compare.

Returns:boolean

true only if the specified object is also a comparator and it imposes the same ordering as this comparator.

naturalOrder back to summary

naturalOrder	back to summary
public static <T extends Comparable<? super T>> Comparator<T> naturalOrder() Returns a comparator that compares `Comparable` objects in natural order. The returned comparator is serializable and throws `NullPointerException` when comparing `null`. Parameters <T> the `Comparable` type of element to be compared Returns:Comparator<T> a comparator that imposes the natural ordering on `Comparable` objects. Annotations @SuppressWarnings:unchecked Since 1.8 See Also `Comparable`

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

Returns a comparator that compares Comparable objects in natural order.

The returned comparator is serializable and throws NullPointerException when comparing null.

Parameters

<T>: the Comparable type of element to be compared

Returns:Comparator<T>

a comparator that imposes the natural ordering on Comparable objects.

Annotations

@SuppressWarnings:unchecked

Since

1.8

See Also

Comparable

nullsFirst back to summary

nullsFirst	back to summary
public static <T> Comparator<T> nullsFirst(Comparator<? super 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. The returned comparator is serializable if the specified comparator is serializable. Parameters <T> the type of the elements to be compared comparator:Comparator<? super T> a `Comparator` for comparing non-null values Returns:Comparator<T> a comparator that considers `null` to be less than non-null, and compares non-null objects with the supplied `Comparator`. Since 1.8

public static <T> Comparator<T> nullsFirst(Comparator<? super 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.

The returned comparator is serializable if the specified comparator is serializable.

Parameters

<T>: the type of the elements to be compared
comparator:Comparator<? super T>: a Comparator for comparing non-null values

Returns:Comparator<T>

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

Since

1.8

nullsLast back to summary

nullsLast	back to summary
public static <T> Comparator<T> nullsLast(Comparator<? super 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. The returned comparator is serializable if the specified comparator is serializable. Parameters <T> the type of the elements to be compared comparator:Comparator<? super T> a `Comparator` for comparing non-null values Returns:Comparator<T> a comparator that considers `null` to be greater than non-null, and compares non-null objects with the supplied `Comparator`. Since 1.8

public static <T> Comparator<T> nullsLast(Comparator<? super 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.

The returned comparator is serializable if the specified comparator is serializable.

Parameters

<T>: the type of the elements to be compared
comparator:Comparator<? super T>: a Comparator for comparing non-null values

Returns:Comparator<T>

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

Since

1.8

reversed	back to summary
public default Comparator<T> reversed() Returns a comparator that imposes the reverse ordering of this comparator. Returns:Comparator<T> a comparator that imposes the reverse ordering of this comparator. Since 1.8

reversed

back to summary

public default Comparator<T> reversed()

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

Returns:Comparator<T>: a comparator that imposes the reverse ordering of this comparator.
Since: 1.8

reverseOrder back to summary

reverseOrder	back to summary
public static <T extends Comparable<? super T>> Comparator<T> reverseOrder() Returns a comparator that imposes the reverse of the natural ordering. The returned comparator is serializable and throws `NullPointerException` when comparing `null`. Parameters <T> the `Comparable` type of element to be compared Returns:Comparator<T> a comparator that imposes the reverse of the natural ordering on `Comparable` objects. Since 1.8 See Also `Comparable`

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

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

The returned comparator is serializable and throws NullPointerException when comparing null.

Parameters

<T>: the Comparable type of element to be compared

Returns:Comparator<T>

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

Since

1.8

See Also

Comparable

thenComparing back to summary

thenComparing	back to summary
public default Comparator<T> thenComparing(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. The returned comparator is serializable if the specified comparator is also serializable. 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);` Parameters other:Comparator<? super T> the other comparator to be used when this comparator compares two objects that are equal. Returns:Comparator<T> a lexicographic-order comparator composed of this and then the other comparator Exceptions NullPointerException: if the argument is null. Since 1.8

public default Comparator<T> thenComparing(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.

The returned comparator is serializable if the specified comparator is also serializable.

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);

Parameters

other:Comparator<? super T>: the other comparator to be used when this comparator compares two objects that are equal.

Returns:Comparator<T>

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

Exceptions

NullPointerException:: if the argument is null.

Since

1.8

thenComparing back to summary

thenComparing	back to summary
public default <U> Comparator<T> thenComparing(Function<? super T, ? extends U> keyExtractor, Comparator<? super U> keyComparator) Returns a lexicographic-order comparator with a function that extracts a key to be compared with the given `Comparator`. Implementation Specification This default implementation behaves as if `thenComparing(comparing(keyExtractor, cmp))`. Parameters <U> the type of the sort key keyExtractor:Function<? super T, ? extends U> the function used to extract the sort key keyComparator:Comparator<? super U> the `Comparator` used to compare the sort key Returns:Comparator<T> a lexicographic-order comparator composed of this comparator and then comparing on the key extracted by the keyExtractor function Exceptions NullPointerException: if either argument is null. Since 1.8 See Also `comparing(Function, Comparator)`, `thenComparing(Comparator)`

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

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

Implementation Specification

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

Parameters

: the type of the sort key
keyExtractor:Function<? super T, ? extends U>: the function used to extract the sort key
keyComparator:Comparator<? super U>: the Comparator used to compare the sort key

Returns:Comparator<T>

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

Exceptions

NullPointerException:: if either argument is null.

Since

1.8

thenComparing back to summary

thenComparing	back to summary
public default <U extends Comparable<? super U>> Comparator<T> thenComparing(Function<? super T, ? extends U> keyExtractor) Returns a lexicographic-order comparator with a function that extracts a `Comparable` sort key. Implementation Specification This default implementation behaves as if `thenComparing(comparing(keyExtractor))`. Parameters <U> the type of the `Comparable` sort key keyExtractor:Function<? super T, ? extends U> the function used to extract the `Comparable` sort key Returns:Comparator<T> a lexicographic-order comparator composed of this and then the `Comparable` sort key. Exceptions NullPointerException: if the argument is null. Since 1.8 See Also `comparing(Function)`, `thenComparing(Comparator)`

public default > Comparator<T> thenComparing(Function<? super T, ? extends U> keyExtractor)

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

Implementation Specification

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

Parameters

: the type of the Comparable sort key
keyExtractor:Function<? super T, ? extends U>: the function used to extract the Comparable sort key

Returns:Comparator<T>

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

Exceptions

NullPointerException:: if the argument is null.

Since

1.8

thenComparingDouble back to summary

thenComparingDouble	back to summary
public default Comparator<T> thenComparingDouble(ToDoubleFunction<? super T> keyExtractor) Returns a lexicographic-order comparator with a function that extracts a `double` sort key. Implementation Specification This default implementation behaves as if `thenComparing(comparingDouble(keyExtractor))`. Parameters keyExtractor:ToDoubleFunction<? super T> the function used to extract the double sort key Returns:Comparator<T> a lexicographic-order comparator composed of this and then the `double` sort key Exceptions NullPointerException: if the argument is null. Since 1.8 See Also `comparingDouble(ToDoubleFunction)`, `thenComparing(Comparator)`

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

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

Implementation Specification

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

Parameters

keyExtractor:ToDoubleFunction<? super T>: the function used to extract the double sort key

Returns:Comparator<T>

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

Exceptions

NullPointerException:: if the argument is null.

Since

1.8

thenComparingInt back to summary

thenComparingInt	back to summary
public default Comparator<T> thenComparingInt(ToIntFunction<? super T> keyExtractor) Returns a lexicographic-order comparator with a function that extracts an `int` sort key. Implementation Specification This default implementation behaves as if `thenComparing(comparingInt(keyExtractor))`. Parameters keyExtractor:ToIntFunction<? super T> the function used to extract the integer sort key Returns:Comparator<T> a lexicographic-order comparator composed of this and then the `int` sort key Exceptions NullPointerException: if the argument is null. Since 1.8 See Also `comparingInt(ToIntFunction)`, `thenComparing(Comparator)`

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

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

Implementation Specification

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

Parameters

keyExtractor:ToIntFunction<? super T>: the function used to extract the integer sort key

Returns:Comparator<T>

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

Exceptions

NullPointerException:: if the argument is null.

Since

1.8

thenComparingLong back to summary

thenComparingLong	back to summary
public default Comparator<T> thenComparingLong(ToLongFunction<? super T> keyExtractor) Returns a lexicographic-order comparator with a function that extracts a `long` sort key. Implementation Specification This default implementation behaves as if `thenComparing(comparingLong(keyExtractor))`. Parameters keyExtractor:ToLongFunction<? super T> the function used to extract the long sort key Returns:Comparator<T> a lexicographic-order comparator composed of this and then the `long` sort key Exceptions NullPointerException: if the argument is null. Since 1.8 See Also `comparingLong(ToLongFunction)`, `thenComparing(Comparator)`

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

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

Implementation Specification

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

Parameters

keyExtractor:ToLongFunction<? super T>: the function used to extract the long sort key

Returns:Comparator<T>

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

Exceptions

NullPointerException:: if the argument is null.

Since

1.8

public Interface Comparator<T>

Method Summary

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