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ADD: Backport of Comparator and Comparators with Java 8 additions.

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Oasis 2018-10-07 17:45:41 +08:00
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library/src/main/java/com/oasisfeng/java/util/Collections.java Normal file
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package com.oasisfeng.java.util;
import java.io.Serializable;
/**
* Created by Oasis on 2018-7-4.
*/
class Collections {
/**
* Returns a comparator that imposes the reverse of the <em>natural
* ordering</em> on a collection of objects that implement the
* {@code Comparable} interface. (The natural ordering is the ordering
* imposed by the objects' own {@code compareTo} method.) This enables a
* simple idiom for sorting (or maintaining) collections (or arrays) of
* objects that implement the {@code Comparable} interface in
* reverse-natural-order. For example, suppose {@code a} is an array of
* strings. Then: <pre>
* Arrays.sort(a, Collections.reverseOrder());
* </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p>
*
* The returned comparator is serializable.
*
* @param <T> the class of the objects compared by the comparator
* @return A comparator that imposes the reverse of the <i>natural
* ordering</i> on a collection of objects that implement
* the <tt>Comparable</tt> interface.
* @see Comparable
*/
@SuppressWarnings("unchecked")
public static <T> Comparator<T> reverseOrder() {
return (Comparator<T>) ReverseComparator.REVERSE_ORDER;
}
/**
* @serial include
*/
private static class ReverseComparator
implements Comparator<Comparable<Object>>, Serializable {
private static final long serialVersionUID = 7207038068494060240L;
static final ReverseComparator REVERSE_ORDER
= new ReverseComparator();
public int compare(Comparable<Object> c1, Comparable<Object> c2) {
return c2.compareTo(c1);
}
private Object readResolve() { return java.util.Collections.reverseOrder(); }
@Override
public Comparator<Comparable<Object>> reversed() {
return Comparators.naturalOrder();
}
}
/**
* Returns a comparator that imposes the reverse ordering of the specified
* comparator.
*
* <p>The returned comparator is serializable (assuming the specified
* comparator is also serializable or {@code null}).
*
* @param <T> the class of the objects compared by the comparator
* @param cmp a comparator who's ordering is to be reversed by the returned
* comparator or {@code null}
* @return A comparator that imposes the reverse ordering of the
* specified comparator.
* @since 1.5
*/
static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
if (cmp instanceof ReverseComparator2)
return ((ReverseComparator2<T>)cmp).cmp;
return new ReverseComparator2<>(cmp);
}
/**
* @serial include
*/
private static class ReverseComparator2<T> implements Comparator<T>,
Serializable
{
private static final long serialVersionUID = 4374092139857L;
/**
* The comparator specified in the static factory. This will never
* be null, as the static factory returns a ReverseComparator
* instance if its argument is null.
*
* @serial
*/
final Comparator<T> cmp;
ReverseComparator2(Comparator<T> cmp) {
assert cmp != null;
this.cmp = cmp;
}
public int compare(T t1, T t2) {
return cmp.compare(t2, t1);
}
public boolean equals(Object o) {
return (o == this) ||
(o instanceof ReverseComparator2 &&
cmp.equals(((ReverseComparator2)o).cmp));
}
public int hashCode() {
return cmp.hashCode() ^ Integer.MIN_VALUE;
}
@Override
public Comparator<T> reversed() {
return cmp;
}
}
}

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library/src/main/java/com/oasisfeng/java/util/Comparator.java Normal file
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/*
* Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package com.oasisfeng.java.util;
import java.io.Serializable;
import java9.util.Objects;
import java9.util.function.Function;
import java9.util.function.ToDoubleFunction;
import java9.util.function.ToIntFunction;
import java9.util.function.ToLongFunction;
/**
* A comparison function, which imposes a <i>total ordering</i> on some
* collection of objects. Comparators can be passed to a sort method (such
* as {@link java.util.Collections#sort(java.util.List,java.util.Comparator) Collections.sort} or {@link
* java.util.Arrays#sort(Object[],java.util.Comparator) 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 {@link java.util.SortedSet sorted sets} or {@link
* java.util.SortedMap sorted maps}), or to provide an ordering for collections of
* objects that don't have a {@link Comparable natural ordering}.<p>
*
* The ordering imposed by a comparator <tt>c</tt> on a set of elements
* <tt>S</tt> is said to be <i>consistent with equals</i> if and only if
* <tt>c.compare(e1, e2)==0</tt> has the same boolean value as
* <tt>e1.equals(e2)</tt> for every <tt>e1</tt> and <tt>e2</tt> in
* <tt>S</tt>.<p>
*
* 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 <tt>c</tt>
* is used with elements (or keys) drawn from a set <tt>S</tt>. If the
* ordering imposed by <tt>c</tt> on <tt>S</tt> 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 <tt>equals</tt>.<p>
*
* For example, suppose one adds two elements {@code a} and {@code b} such that
* {@code (a.equals(b) && c.compare(a, b) != 0)}
* to an empty {@code TreeSet} with comparator {@code c}.
* The second {@code add} operation will return
* true (and the size of the tree set will increase) because {@code a} and
* {@code b} are not equivalent from the tree set's perspective, even though
* this is contrary to the specification of the
* {@link java.util.Set#add Set.add} method.<p>
*
* Note: It is generally a good idea for comparators to also implement
* <tt>java.io.Serializable</tt>, as they may be used as ordering methods in
* serializable data structures (like {@link java.util.TreeSet}, {@link java.util.TreeMap}). In
* order for the data structure to serialize successfully, the comparator (if
* provided) must implement <tt>Serializable</tt>.<p>
*
* For the mathematically inclined, the <i>relation</i> that defines the
* <i>imposed ordering</i> that a given comparator <tt>c</tt> imposes on a
* given set of objects <tt>S</tt> is:<pre>
* {(x, y) such that c.compare(x, y) &lt;= 0}.
* </pre> The <i>quotient</i> for this total order is:<pre>
* {(x, y) such that c.compare(x, y) == 0}.
* </pre>
*
* It follows immediately from the contract for <tt>compare</tt> that the
* quotient is an <i>equivalence relation</i> on <tt>S</tt>, and that the
* imposed ordering is a <i>total order</i> on <tt>S</tt>. When we say that
* the ordering imposed by <tt>c</tt> on <tt>S</tt> is <i>consistent with
* equals</i>, we mean that the quotient for the ordering is the equivalence
* relation defined by the objects' {@link Object#equals(Object)
* equals(Object)} method(s):<pre>
* {(x, y) such that x.equals(y)}. </pre>
*
* <p>Unlike {@code Comparable}, a comparator may optionally permit
* comparison of null arguments, while maintaining the requirements for
* an equivalence relation.
*
* <p>This interface is a member of the
* <a href="{@docRoot}openjdk-redirect.html?v=8&path=/technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @param <T> the type of objects that may be compared by this comparator
*
* @author Josh Bloch
* @author Neal Gafter
* @see Comparable
* @see java.io.Serializable
* @since 1.2
*/
@FunctionalInterface
public interface Comparator<T> extends java.util.Comparator<T> {
/**
* Returns a comparator that imposes the reverse ordering of this
* comparator.
*
* @return a comparator that imposes the reverse ordering of this
* comparator.
* @since 1.8
*/
default Comparator<T> reversed() {
return Collections.reverseOrder(this);
}
/**
* Returns a lexicographic-order comparator with another comparator.
* If this {@code Comparator} considers two elements equal, i.e.
* {@code compare(a, b) == 0}, {@code other} is used to determine the order.
*
* <p>The returned comparator is serializable if the specified comparator
* is also serializable.
*
* @apiNote
* For example, to sort a collection of {@code String} based on the length
* and then case-insensitive natural ordering, the comparator can be
* composed using following code,
*
* <pre>{@code
* Comparator<String> cmp = Comparator.comparingInt(String::length)
* .thenComparing(String.CASE_INSENSITIVE_ORDER);
* }</pre>
*
* @param other the other comparator to be used when this comparator
* compares two objects that are equal.
* @return a lexicographic-order comparator composed of this and then the
* other comparator
* @throws NullPointerException if the argument is null.
* @since 1.8
*/
default Comparator<T> thenCompare(Comparator<? super T> other) {
Objects.requireNonNull(other);
return (Comparator<T> & Serializable) (c1, c2) -> {
int res = compare(c1, c2);
return (res != 0) ? res : other.compare(c1, c2);
};
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a key to be compared with the given {@code Comparator}.
*
* @implSpec This default implementation behaves as if {@code
* thenComparing(comparing(keyExtractor, cmp))}.
*
* @param <U> the type of the sort key
* @param keyExtractor the function used to extract the sort key
* @param keyComparator the {@code Comparator} used to compare the sort key
* @return 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 Comparators#comparing(Function, Comparator)
* @see #thenCompare(Comparator)
* @since 1.8
*/
default <U> Comparator<T> thenCompare(
Function<? super T, ? extends U> keyExtractor,
Comparator<? super U> keyComparator)
{
return thenCompare(Comparators.comparing(keyExtractor, keyComparator));
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a {@code Comparable} sort key.
*
* @implSpec This default implementation behaves as if {@code
* thenComparing(comparing(keyExtractor))}.
*
* @param <U> the type of the {@link Comparable} sort key
* @param keyExtractor the function used to extract the {@link
* Comparable} sort key
* @return a lexicographic-order comparator composed of this and then the
* {@link Comparable} sort key.
* @throws NullPointerException if the argument is null.
* @see Comparators#comparing(Function)
* @see #thenCompare(Comparator)
* @since 1.8
*/
default <U extends Comparable<? super U>> Comparator<T> thenCompare(
Function<? super T, ? extends U> keyExtractor)
{
return thenCompare(Comparators.comparing(keyExtractor));
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a {@code int} sort key.
*
* @implSpec This default implementation behaves as if {@code
* thenComparing(comparingInt(keyExtractor))}.
*
* @param keyExtractor the function used to extract the integer sort key
* @return a lexicographic-order comparator composed of this and then the
* {@code int} sort key
* @throws NullPointerException if the argument is null.
* @see Comparators#comparingInt(ToIntFunction)
* @see #thenCompare(Comparator)
* @since 1.8
*/
default Comparator<T> thenCompareInt(ToIntFunction<? super T> keyExtractor) {
return thenCompare(Comparators.comparingInt(keyExtractor));
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a {@code long} sort key.
*
* @implSpec This default implementation behaves as if {@code
* thenComparing(comparingLong(keyExtractor))}.
*
* @param keyExtractor the function used to extract the long sort key
* @return a lexicographic-order comparator composed of this and then the
* {@code long} sort key
* @throws NullPointerException if the argument is null.
* @see Comparators#comparingLong(ToLongFunction)
* @see #thenCompare(Comparator)
* @since 1.8
*/
default Comparator<T> thenComparingLong(ToLongFunction<? super T> keyExtractor) {
return thenCompare(Comparators.comparingLong(keyExtractor));
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a {@code double} sort key.
*
* @implSpec This default implementation behaves as if {@code
* thenComparing(comparingDouble(keyExtractor))}.
*
* @param keyExtractor the function used to extract the double sort key
* @return a lexicographic-order comparator composed of this and then the
* {@code double} sort key
* @throws NullPointerException if the argument is null.
* @see Comparators#comparingDouble(ToDoubleFunction)
* @see #thenCompare(Comparator)
* @since 1.8
*/
default Comparator<T> thenComparingDouble(ToDoubleFunction<? super T> keyExtractor) {
return thenCompare(Comparators.comparingDouble(keyExtractor));
}
}

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/*
* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package com.oasisfeng.java.util;
import java.io.Serializable;
import java9.lang.Integers;
import java9.lang.Longs;
import java9.util.Objects;
import java9.util.function.Function;
import java9.util.function.ToDoubleFunction;
import java9.util.function.ToIntFunction;
import java9.util.function.ToLongFunction;
/**
* A place for static default implementations of the new Java 8
* default interface methods and static interface methods in the
* {@link Comparator} interface.
*/
public final class Comparators {
/**
* Compares {@link Comparable} objects in natural order.
*
* @see Comparable
*/
private enum NaturalOrderComparator implements Comparator<Comparable<Object>> {
INSTANCE;
@Override
public int compare(Comparable<Object> c1, Comparable<Object> c2) {
return c1.compareTo(c2);
}
public Comparator<Comparable<Object>> reversed() {
return Comparators.reverseOrder();
}
}
/**
* Null-friendly comparators
*/
private static final class NullComparator<T> implements Comparator<T>, Serializable {
private static final long serialVersionUID = -7569533591570686392L;
private final boolean nullFirst;
// if null, non-null Ts are considered equal
private final Comparator<T> real;
@SuppressWarnings("unchecked")
NullComparator(boolean nullFirst, Comparator<? super T> real) {
this.nullFirst = nullFirst;
this.real = (Comparator<T>) real;
}
@Override
public int compare(T a, T b) {
if (a == null) {
return (b == null) ? 0 : (nullFirst ? -1 : 1);
} else if (b == null) {
return nullFirst ? 1: -1;
} else {
return (real == null) ? 0 : real.compare(a, b);
}
}
public Comparator<T> thenComparing(Comparator<? super T> other) {
Objects.requireNonNull(other);
return new NullComparator<T>(nullFirst, real == null ? other : Comparators.thenComparing(real, other));
}
public Comparator<T> reversed() {
return new NullComparator<T>(!nullFirst, real == null ? null : Collections.reverseOrder(real));
}
}
/**
* Returns a comparator that imposes the reverse of the <em>natural
* ordering</em>.
*
* <p>The returned comparator is serializable and throws {@link
* NullPointerException} when comparing {@code null}.
*
* @param <T> the {@link Comparable} type of element to be compared
* @return a comparator that imposes the reverse of the <i>natural
* ordering</i> on {@code Comparable} objects.
* @see Comparable
* @since 1.8
*/
public static <T extends Comparable<? super T>> Comparator<T> reverseOrder() {
return Collections.reverseOrder();
}
/**
* Returns a comparator that compares {@link Comparable} objects in natural
* order.
*
* <p>The returned comparator is serializable and throws {@link
* NullPointerException} when comparing {@code null}.
*
* @param <T> the {@link Comparable} type of element to be compared
* @return a comparator that imposes the <i>natural ordering</i> on {@code
* Comparable} objects.
* @see Comparable
* @since 1.8
*/
@SuppressWarnings("unchecked")
public static <T extends Comparable<? super T>> Comparator<T> naturalOrder() {
return (Comparator<T>) Comparators.NaturalOrderComparator.INSTANCE;
}
/**
* Accepts a function that extracts a sort key from a type {@code T}, and
* returns a {@code Comparator<T>} that compares by that sort key using
* the specified {@link Comparator}.
*
* <p>The returned comparator is serializable if the specified function
* and comparator are both serializable.
*
* <p><b>API Note:</b><br>
* For example, to obtain a {@code Comparator} that compares {@code
* Person} objects by their last name ignoring case differences,
*
* <pre>{@code
* Comparator<Person> cmp = Comparators.comparing(
* Person::getLastName,
* String.CASE_INSENSITIVE_ORDER);
* }</pre>
*
* @param <T> the type of element to be compared
* @param <U> the type of the sort key
* @param keyExtractor the function used to extract the sort key
* @param keyComparator the {@code Comparator} used to compare the sort key
* @return a comparator that compares by an extracted key using the
* specified {@code Comparator}
* @throws 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)
{
Objects.requireNonNull(keyExtractor);
Objects.requireNonNull(keyComparator);
return (Comparator<T> & Serializable)
(c1, c2) -> keyComparator.compare(keyExtractor.apply(c1),
keyExtractor.apply(c2));
}
/**
* Accepts a function that extracts a {@link java.lang.Comparable
* Comparable} sort key from a type {@code T}, and returns a {@code
* Comparator<T>} that compares by that sort key.
*
* <p>The returned comparator is serializable if the specified function
* is also serializable.
*
* <p><b>API Note:</b><br>
* For example, to obtain a {@code Comparator} that compares {@code
* Person} objects by their last name,
*
* <pre>{@code
* Comparator<Person> byLastName = Comparators.comparing(Person::getLastName);
* }</pre>
*
* @param <T> the type of element to be compared
* @param <U> the type of the {@code Comparable} sort key
* @param keyExtractor the function used to extract the {@link
* Comparable} sort key
* @return a comparator that compares by an extracted key
* @throws 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)
{
Objects.requireNonNull(keyExtractor);
return (Comparator<T> & Serializable)
(c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2));
}
/**
* Accepts a function that extracts an {@code int} sort key from a type
* {@code T}, and returns a {@code Comparator<T>} that compares by that
* sort key.
*
* <p>The returned comparator is serializable if the specified function
* is also serializable.
*
* @param <T> the type of element to be compared
* @param keyExtractor the function used to extract the integer sort key
* @return a comparator that compares by an extracted key
* @see #comparing(Function)
* @throws NullPointerException if the argument is null
* @since 1.8
*/
public static <T> Comparator<T> comparingInt(ToIntFunction<? super T> keyExtractor) {
Objects.requireNonNull(keyExtractor);
return (Comparator<T> & Serializable)
(c1, c2) -> Integers.compare(keyExtractor.applyAsInt(c1), keyExtractor.applyAsInt(c2));
}
/**
* Accepts a function that extracts a {@code long} sort key from a type
* {@code T}, and returns a {@code Comparator<T>} that compares by that
* sort key.
*
* <p>The returned comparator is serializable if the specified function is
* also serializable.
*
* @param <T> the type of element to be compared
* @param keyExtractor the function used to extract the long sort key
* @return a comparator that compares by an extracted key
* @see #comparing(Function)
* @throws NullPointerException if the argument is null
* @since 1.8
*/
public static <T> Comparator<T> comparingLong(ToLongFunction<? super T> keyExtractor) {
Objects.requireNonNull(keyExtractor);
return (Comparator<T> & Serializable)
(c1, c2) -> Longs.compare(keyExtractor.applyAsLong(c1), keyExtractor.applyAsLong(c2));
}
/**
* Accepts a function that extracts a {@code double} sort key from a type
* {@code T}, and returns a {@code Comparator<T>} that compares by that
* sort key.
*
* <p>The returned comparator is serializable if the specified function
* is also serializable.
*
* @param <T> the type of element to be compared
* @param keyExtractor the function used to extract the double sort key
* @return a comparator that compares by an extracted key
* @see #comparing(Function)
* @throws NullPointerException if the argument is null
* @since 1.8
*/
public static<T> Comparator<T> comparingDouble(ToDoubleFunction<? super T> keyExtractor) {
Objects.requireNonNull(keyExtractor);
return (Comparator<T> & Serializable)
(c1, c2) -> Double.compare(keyExtractor.applyAsDouble(c1), keyExtractor.applyAsDouble(c2));
}
/**
* Returns a lexicographic-order comparator with another comparator.
* If the {@code this_} {@code Comparator} considers two elements equal, i.e.
* {@code compare(a, b) == 0}, {@code other} is used to determine the order.
*
* <p>The returned comparator is serializable if the specified comparators
* are also serializable.
*
* <p><b>API Note:</b><br>
* For example, to sort a collection of {@code String} based on the length
* and then case-insensitive natural ordering, the comparators can be
* composed using following code,
*
* <pre>{@code
* Comparator<String> cmp = Comparators.thenComparing(Comparators.comparingInt(String::length),
* String.CASE_INSENSITIVE_ORDER);
* }</pre>
*
* @param <T> the type of objects that may be compared by the passed comparators
* @param this_ the comparator to be used first
* @param other the other comparator to be used when the {@code this_} comparator
* compares two objects that are equal.
* @return a lexicographic-order comparator composed of the {@code this_} and then the
* other comparator
* @throws NullPointerException if {@code this_} is null.
* @throws NullPointerException if {@code other} is null.
* @since 1.8
*/
public static <T> Comparator<T> thenComparing(Comparator<? super T> this_, Comparator<? super T> other) {
Objects.requireNonNull(this_);
Objects.requireNonNull(other);
if (this_ instanceof NullComparator) {
return ((NullComparator<T>) this_).thenComparing(other);
}
return (Comparator<T> & Serializable) (c1, c2) -> {
int res = this_.compare(c1, c2);
return (res != 0) ? res : other.compare(c1, c2);
};
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a key to be compared with the given {@code Comparator}.
*
* <p><b>Implementation Requirements:</b><br> This default implementation behaves as if {@code
* thenComparing(this_, comparing(keyExtractor, keyComparator))}.
*
* @param <T> the type of objects that may be compared by the {@code this_} comparator
* @param <U> the type of the sort key
* @param this_ the comparator to be used first
* @param keyExtractor the function used to extract the sort key
* @param keyComparator the {@code Comparator} used to compare the sort key
* @return a lexicographic-order comparator composed of the {@code this_} comparator
* and then comparing on the key extracted by the keyExtractor function
* @throws NullPointerException if either argument is null.
* @see #comparing(Function, Comparator)
* @see #thenComparing(Comparator, Comparator)
* @since 1.8
*/
public static <T, U> Comparator<T> thenComparing(
Comparator<? super T> this_,
Function<? super T, ? extends U> keyExtractor,
Comparator<? super U> keyComparator)
{
return thenComparing(this_, comparing(keyExtractor, keyComparator));
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a {@code Comparable} sort key.
*
* <p><b>Implementation Requirements:</b><br> This default implementation behaves as if {@code
* thenComparing(this_, comparing(keyExtractor))}.
*
* @param <T> the type of objects that may be compared by the {@code this_} comparator
* @param <U> the type of the {@link Comparable} sort key
* @param this_ the comparator to be used first
* @param keyExtractor the function used to extract the {@link
* Comparable} sort key
* @return a lexicographic-order comparator composed of {@code this_} and then the
* {@link Comparable} sort key.
* @throws NullPointerException if either argument is null.
* @see #comparing(Function)
* @see #thenComparing(Comparator, Comparator)
* @since 1.8
*/
public static <T, U extends Comparable<? super U>> Comparator<T> thenComparing(
Comparator<? super T> this_,
Function<? super T, ? extends U> keyExtractor)
{
return thenComparing(this_, comparing(keyExtractor));
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a {@code int} sort key.
*
* <p><b>Implementation Requirements:</b><br> This default implementation behaves as if {@code
* thenComparing(this_, comparingInt(keyExtractor))}.
*
* @param <T> the type of objects that may be compared by the {@code this_} comparator
* @param this_ the comparator to be used first
* @param keyExtractor the function used to extract the integer sort key
* @return a lexicographic-order comparator composed of {@code this_} and then the
* {@code int} sort key
* @throws NullPointerException if either argument is null.
* @see #comparingInt(ToIntFunction)
* @see #thenComparing(Comparator, Comparator)
* @since 1.8
*/
public static <T> Comparator<T> thenComparingInt(Comparator<? super T> this_, ToIntFunction<? super T> keyExtractor) {
return thenComparing(this_, comparingInt(keyExtractor));
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a {@code long} sort key.
*
* <p><b>Implementation Requirements:</b><br> This default implementation behaves as if {@code
* thenComparing(this_, comparingLong(keyExtractor))}.
*
* @param <T> the type of objects that may be compared by the {@code this_} comparator
* @param this_ the comparator to be used first
* @param keyExtractor the function used to extract the long sort key
* @return a lexicographic-order comparator composed of {@code this_} and then the
* {@code long} sort key
* @throws NullPointerException if either argument is null.
* @see #comparingLong(ToLongFunction)
* @see #thenComparing(Comparator, Comparator)
* @since 1.8
*/
public static <T> Comparator<T> thenComparingLong(Comparator<? super T> this_, ToLongFunction<? super T> keyExtractor) {
return thenComparing(this_, comparingLong(keyExtractor));
}
/**
* Returns a lexicographic-order comparator with a function that
* extracts a {@code double} sort key.
*
* <p><b>Implementation Requirements:</b><br> This default implementation behaves as if {@code
* thenComparing(this_, comparingDouble(keyExtractor))}.
*
* @param <T> the type of objects that may be compared by the {@code this_} comparator
* @param this_ the comparator to be used first
* @param keyExtractor the function used to extract the double sort key
* @return a lexicographic-order comparator composed of {@code this_} and then the
* {@code double} sort key
* @throws NullPointerException if either argument is null.
* @see #comparingDouble(ToDoubleFunction)
* @see #thenComparing(Comparator, Comparator)
* @since 1.8
*/
public static <T> Comparator<T> thenComparingDouble(Comparator<? super T> this_, ToDoubleFunction<? super T> keyExtractor) {
return thenComparing(this_, comparingDouble(keyExtractor));
}
/**
* Returns a comparator that imposes the reverse ordering of the
* passed {@code comparator}.
*
* @param <T> the type of objects that may be compared by the comparator argument
* @param comparator the comparator whose ordering needs to be reversed
* @return a comparator that imposes the reverse ordering of the
* passed {@code comparator}.
* @since 1.8
*/
public static <T> Comparator<T> reversed(Comparator<T> comparator) {
if (comparator instanceof NullComparator) {
return ((NullComparator<T>) comparator).reversed();
}
return Collections.reverseOrder(comparator);
}
/**
* Returns a null-friendly comparator that considers {@code null} to be
* less than non-null. When both are {@code null}, they are considered
* equal. If both are non-null, the specified {@code Comparator} is used
* to determine the order. If the specified comparator is {@code null},
* then the returned comparator considers all non-null values to be equal.
*
* <p>The returned comparator is serializable if the specified comparator
* is serializable.
*
* @param <T> the type of the elements to be compared
* @param comparator a {@code Comparator} for comparing non-null values
* @return a comparator that considers {@code null} to be less than
* non-null, and compares non-null objects with the supplied
* {@code Comparator}.
* @since 1.8
*/
public static <T> Comparator<T> nullsFirst(Comparator<? super T> comparator) {
return new Comparators.NullComparator<>(true, comparator);
}
/**
* Returns a null-friendly comparator that considers {@code null} to be
* greater than non-null. When both are {@code null}, they are considered
* equal. If both are non-null, the specified {@code Comparator} is used
* to determine the order. If the specified comparator is {@code null},
* then the returned comparator considers all non-null values to be equal.
*
* <p>The returned comparator is serializable if the specified comparator
* is serializable.
*
* @param <T> the type of the elements to be compared
* @param comparator a {@code Comparator} for comparing non-null values
* @return a comparator that considers {@code null} to be greater than
* non-null, and compares non-null objects with the supplied
* {@code Comparator}.
* @since 1.8
*/
public static <T> Comparator<T> nullsLast(Comparator<? super T> comparator) {
return new Comparators.NullComparator<>(false, comparator);
}
private Comparators() {
}
}