8001667: Comparator combinators and extension methods
Reviewed-by: mduigou, briangoetz
diff --git a/jdk/make/java/java/FILES_java.gmk b/jdk/make/java/java/FILES_java.gmk
index 8c2f80c..189b9fc 100644
--- a/jdk/make/java/java/FILES_java.gmk
+++ b/jdk/make/java/java/FILES_java.gmk
@@ -257,6 +257,7 @@
sun/util/calendar/ZoneInfoFile.java \
java/util/TooManyListenersException.java \
java/util/Comparator.java \
+ java/util/Comparators.java \
java/util/Collections.java \
java/util/Iterator.java \
java/util/ListIterator.java \
diff --git a/jdk/src/share/classes/java/util/Collections.java b/jdk/src/share/classes/java/util/Collections.java
index 58eae6f..b6bac48 100644
--- a/jdk/src/share/classes/java/util/Collections.java
+++ b/jdk/src/share/classes/java/util/Collections.java
@@ -3759,7 +3759,7 @@
return c2.compareTo(c1);
}
- private Object readResolve() { return reverseOrder(); }
+ private Object readResolve() { return Collections.reverseOrder(); }
}
/**
diff --git a/jdk/src/share/classes/java/util/Comparator.java b/jdk/src/share/classes/java/util/Comparator.java
index 35ead37..017c2e7 100644
--- a/jdk/src/share/classes/java/util/Comparator.java
+++ b/jdk/src/share/classes/java/util/Comparator.java
@@ -25,6 +25,11 @@
package java.util;
+import java.util.function.Function;
+import java.util.function.ToIntFunction;
+import java.util.function.ToLongFunction;
+import java.util.function.ToDoubleFunction;
+
/**
* A comparison function, which imposes a <i>total ordering</i> on some
* collection of objects. Comparators can be passed to a sort method (such
@@ -165,4 +170,93 @@
* @see Object#hashCode()
*/
boolean equals(Object obj);
+
+ /**
+ * 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> reverseOrder() {
+ return Collections.reverseOrder(this);
+ }
+
+ /**
+ * Constructs a lexicographic order comparator with another comparator.
+ * For example, a {@code Comparator<Person> byLastName} can be composed
+ * with another {@code Comparator<Person> byFirstName}, then {@code
+ * byLastName.thenComparing(byFirstName)} creates a {@code
+ * Comparator<Person>} which sorts by last name, and for equal last names
+ * sorts by first name.
+ *
+ * @param other the other comparator used when equals on this.
+ * @throws NullPointerException if the argument is null.
+ * @since 1.8
+ */
+ default Comparator<T> thenComparing(Comparator<? super T> other) {
+ return Comparators.compose(this, other);
+ }
+
+ /**
+ * Constructs a lexicographic order comparator with a function that
+ * extracts a {@code Comparable} key. This default implementation calls
+ * {@code thenComparing(this, Comparators.comparing(keyExtractor))}.
+ *
+ * @param <U> the {@link Comparable} type for comparison
+ * @param keyExtractor the function used to extract the {@link Comparable} sort key
+ * @throws NullPointerException if the argument is null.
+ * @see Comparators#comparing(Function)
+ * @see #thenComparing(Comparator)
+ * @since 1.8
+ */
+ default <U extends Comparable<? super U>> Comparator<T> thenComparing(Function<? super T, ? extends U> keyExtractor) {
+ return thenComparing(Comparators.comparing(keyExtractor));
+ }
+
+ /**
+ * Constructs a lexicographic order comparator with a function that
+ * extracts a {@code int} value. This default implementation calls {@code
+ * thenComparing(this, Comparators.comparing(keyExtractor))}.
+ *
+ * @param keyExtractor the function used to extract the integer value
+ * @throws NullPointerException if the argument is null.
+ * @see Comparators#comparing(ToIntFunction)
+ * @see #thenComparing(Comparator)
+ * @since 1.8
+ */
+ default Comparator<T> thenComparing(ToIntFunction<? super T> keyExtractor) {
+ return thenComparing(Comparators.comparing(keyExtractor));
+ }
+
+ /**
+ * Constructs a lexicographic order comparator with a function that
+ * extracts a {@code long} value. This default implementation calls
+ * {@code thenComparing(this, Comparators.comparing(keyExtractor))}.
+ *
+ * @param keyExtractor the function used to extract the long value
+ * @throws NullPointerException if the argument is null.
+ * @see Comparators#comparing(ToLongFunction)
+ * @see #thenComparing(Comparator)
+ * @since 1.8
+ */
+ default Comparator<T> thenComparing(ToLongFunction<? super T> keyExtractor) {
+ return thenComparing(Comparators.comparing(keyExtractor));
+ }
+
+ /**
+ * Constructs a lexicographic order comparator with a function that
+ * extracts a {@code double} value. This default implementation calls
+ * {@code thenComparing(this, Comparators.comparing(keyExtractor))}.
+ *
+ * @param keyExtractor the function used to extract the double value
+ * @throws NullPointerException if the argument is null.
+ * @see Comparators#comparing(ToDoubleFunction)
+ * @see #thenComparing(Comparator)
+ * @since 1.8
+ */
+ default Comparator<T> thenComparing(ToDoubleFunction<? super T> keyExtractor) {
+ return thenComparing(Comparators.comparing(keyExtractor));
+ }
}
diff --git a/jdk/src/share/classes/java/util/Comparators.java b/jdk/src/share/classes/java/util/Comparators.java
new file mode 100644
index 0000000..7582133
--- /dev/null
+++ b/jdk/src/share/classes/java/util/Comparators.java
@@ -0,0 +1,279 @@
+/*
+ * Copyright (c) 2012, 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 java.util;
+
+import java.io.Serializable;
+import java.util.function.BinaryOperator;
+import java.util.function.Function;
+import java.util.function.ToDoubleFunction;
+import java.util.function.ToIntFunction;
+import java.util.function.ToLongFunction;
+
+/**
+ * This class consists of {@code static} utility methods for comparators. Mostly
+ * factory method that returns a {@link Comparator}.
+ *
+ * <p> Unless otherwise noted, passing a {@code null} argument to a method in
+ * this class will cause a {@link NullPointerException} to be thrown.
+ *
+ * @see Comparator
+ * @since 1.8
+ */
+public class Comparators {
+ private Comparators() {
+ throw new AssertionError("no instances");
+ }
+
+ /**
+ * 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);
+ }
+ }
+
+ /**
+ * Returns a comparator that imposes the reverse of the <em>natural
+ * ordering</em>.
+ *
+ * <p>The returned comparator is serializable.
+ *
+ * @param <T> {@link Comparable} type
+ *
+ * @return A comparator that imposes the reverse of the <i>natural
+ * ordering</i> on a collection of objects that implement
+ * the {@link Comparable} interface.
+ * @see Comparable
+ */
+ public static <T extends Comparable<? super T>> Comparator<T> reverseOrder() {
+ return Collections.reverseOrder();
+ }
+
+ /**
+ * Returns a comparator that imposes the reverse ordering of the specified
+ * {@link Comparator}.
+ *
+ * <p>The returned comparator is serializable (assuming the specified
+ * comparator is also serializable).
+ *
+ * @param <T> the element type to be compared
+ * @param cmp a comparator whose ordering is to be reversed by the returned
+ * comparator
+ * @return A comparator that imposes the reverse ordering of the
+ * specified comparator.
+ */
+ public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
+ Objects.requireNonNull(cmp);
+ return Collections.reverseOrder(cmp);
+ }
+
+ /**
+ * Gets a comparator compares {@link Comparable} type in natural order.
+ *
+ * @param <T> {@link Comparable} type
+ */
+ public static <T extends Comparable<? super T>> Comparator<T> naturalOrder() {
+ return (Comparator<T>) NaturalOrderComparator.INSTANCE;
+ }
+
+ /**
+ * Gets a comparator compares {@link Map.Entry} in natural order on key.
+ *
+ * @param <K> {@link Comparable} key type
+ * @param <V> value type
+ */
+ public static <K extends Comparable<? super K>, V> Comparator<Map.Entry<K,V>> naturalOrderKeys() {
+ return (Comparator<Map.Entry<K, V>> & Serializable)
+ (c1, c2) -> c1.getKey().compareTo(c2.getKey());
+ }
+
+ /**
+ * Gets a comparator compares {@link Map.Entry} in natural order on value.
+ *
+ * @param <K> key type
+ * @param <V> {@link Comparable} value type
+ */
+ public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> naturalOrderValues() {
+ return (Comparator<Map.Entry<K, V>> & Serializable)
+ (c1, c2) -> c1.getValue().compareTo(c2.getValue());
+ }
+
+ /**
+ * Gets a comparator compares {@link Map.Entry} by key using the given
+ * {@link Comparator}.
+ *
+ * <p>The returned comparator is serializable assuming the specified
+ * comparators are also serializable.
+ *
+ * @param <K> key type
+ * @param <V> value type
+ * @param cmp the key {@link Comparator}
+ */
+ public static <K, V> Comparator<Map.Entry<K, V>> byKey(Comparator<? super K> cmp) {
+ Objects.requireNonNull(cmp);
+ return (Comparator<Map.Entry<K, V>> & Serializable)
+ (c1, c2) -> cmp.compare(c1.getKey(), c2.getKey());
+ }
+
+ /**
+ * Gets a comparator compares {@link Map.Entry} by value using the given
+ * {@link Comparator}.
+ *
+ * @param <K> key type
+ * @param <V> value type
+ * @param cmp the value {@link Comparator}
+ */
+ public static <K, V> Comparator<Map.Entry<K, V>> byValue(Comparator<? super V> cmp) {
+ Objects.requireNonNull(cmp);
+ return (Comparator<Map.Entry<K, V>> & Serializable)
+ (c1, c2) -> cmp.compare(c1.getValue(), c2.getValue());
+ }
+
+ /**
+ * 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. For example, if a class
+ * {@code Person} has a {@code String}-valued getter {@code getLastName},
+ * then {@code comparing(Person::getLastName)} would return a {@code
+ * Comparator<Person>} that compares {@code Person} objects by their last
+ * name.
+ *
+ * @param <T> the original element type
+ * @param <U> the {@link Comparable} type for comparison
+ * @param keyExtractor the function used to extract the {@link Comparable} sort key
+ */
+ 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} value from a type {@code
+ * T}, and returns a {@code Comparator<T>} that compares by that value.
+ *
+ * <p>The returned comparator is serializable assuming the specified
+ * function is also serializable.
+ *
+ * @see #comparing(Function)
+ * @param <T> the original element type
+ * @param keyExtractor the function used to extract the integer value
+ */
+ public static <T> Comparator<T> comparing(ToIntFunction<? super T> keyExtractor) {
+ Objects.requireNonNull(keyExtractor);
+ return (Comparator<T> & Serializable)
+ (c1, c2) -> Integer.compare(keyExtractor.applyAsInt(c1), keyExtractor.applyAsInt(c2));
+ }
+
+ /**
+ * Accepts a function that extracts a {@code long} value from a type {@code
+ * T}, and returns a {@code Comparator<T>} that compares by that value.
+ *
+ * <p>The returned comparator is serializable assuming the specified
+ * function is also serializable.
+ *
+ * @see #comparing(Function)
+ * @param <T> the original element type
+ * @param keyExtractor the function used to extract the long value
+ */
+ public static <T> Comparator<T> comparing(ToLongFunction<? super T> keyExtractor) {
+ Objects.requireNonNull(keyExtractor);
+ return (Comparator<T> & Serializable)
+ (c1, c2) -> Long.compare(keyExtractor.applyAsLong(c1), keyExtractor.applyAsLong(c2));
+ }
+
+ /**
+ * Accepts a function that extracts a {@code double} value from a type
+ * {@code T}, and returns a {@code Comparator<T>} that compares by that
+ * value.
+ *
+ * <p>The returned comparator is serializable assuming the specified
+ * function is also serializable.
+ *
+ * @see #comparing(Function)
+ * @param <T> the original element type
+ * @param keyExtractor the function used to extract the double value
+ */
+ public static<T> Comparator<T> comparing(ToDoubleFunction<? super T> keyExtractor) {
+ Objects.requireNonNull(keyExtractor);
+ return (Comparator<T> & Serializable)
+ (c1, c2) -> Double.compare(keyExtractor.applyAsDouble(c1), keyExtractor.applyAsDouble(c2));
+ }
+
+ /**
+ * Constructs a lexicographic order from two {@link Comparator}s. For
+ * example, if you have comparators {@code byLastName} and {@code
+ * byFirstName}, each of type {@code Comparator<Person>}, then {@code
+ * compose(byLastName, byFirstName)} creates a {@code Comparator<Person>}
+ * which sorts by last name, and for equal last names sorts by first name.
+ *
+ * <p>The returned comparator is serializable assuming the specified
+ * comparators are also serializable.
+ *
+ * @param <T> the element type to be compared
+ * @param first the first comparator
+ * @param second the secondary comparator used when equals on the first
+ */
+ public static<T> Comparator<T> compose(Comparator<? super T> first, Comparator<? super T> second) {
+ Objects.requireNonNull(first);
+ Objects.requireNonNull(second);
+ return (Comparator<T> & Serializable) (c1, c2) -> {
+ int res = first.compare(c1, c2);
+ return (res != 0) ? res : second.compare(c1, c2);
+ };
+ }
+
+ /**
+ * Constructs a {@link BinaryOperator} which returns the lesser of two elements
+ * according to the specified {@code Comparator}
+ *
+ * @param comparator A {@code Comparator} for comparing the two values
+ * @param <T> the type of the elements to be compared
+ * @return a {@code BinaryOperator} which returns the lesser of its operands,
+ * according to the supplied {@code Comparator}
+ */
+ public static<T> BinaryOperator<T> lesserOf(Comparator<? super T> comparator) {
+ return (a, b) -> comparator.compare(a, b) <= 0 ? a : b;
+ }
+
+ /**
+ * Constructs a {@link BinaryOperator} which returns the greater of two elements
+ * according to the specified {@code Comparator}
+ *
+ * @param comparator A {@code Comparator} for comparing the two values
+ * @param <T> the type of the elements to be compared
+ * @return a {@code BinaryOperator} which returns the greater of its operands,
+ * according to the supplied {@code Comparator}
+ */
+ public static<T> BinaryOperator<T> greaterOf(Comparator<? super T> comparator) {
+ return (a, b) -> comparator.compare(a, b) >= 0 ? a : b;
+ }
+}
diff --git a/jdk/test/java/util/Collections/ReverseOrder.java b/jdk/test/java/util/Collections/ReverseOrder.java
index d4fed08..9831b57 100644
--- a/jdk/test/java/util/Collections/ReverseOrder.java
+++ b/jdk/test/java/util/Collections/ReverseOrder.java
@@ -23,23 +23,56 @@
/*
* @test
- * @bug 4593209
+ * @bug 4593209 8001667
* @summary Reverse comparator was subtly broken
* @author Josh bloch
*/
import java.util.*;
+import java.io.*;
public class ReverseOrder {
+ static byte[] serialBytes(Object o) {
+ try {
+ ByteArrayOutputStream bos = new ByteArrayOutputStream();
+ ObjectOutputStream oos = new ObjectOutputStream(bos);
+ oos.writeObject(o);
+ oos.flush();
+ oos.close();
+ return bos.toByteArray();
+ } catch (Throwable t) {
+ throw new Error(t);
+ }
+ }
+
+ @SuppressWarnings("unchecked")
+ static <T> T serialClone(T o) {
+ try {
+ ObjectInputStream ois = new ObjectInputStream
+ (new ByteArrayInputStream(serialBytes(o)));
+ T clone = (T) ois.readObject();
+ return clone;
+ } catch (Throwable t) {
+ throw new Error(t);
+ }
+ }
+
public static void main(String[] args) throws Exception {
Foo[] a = { new Foo(2), new Foo(3), new Foo(1) };
List list = Arrays.asList(a);
- Collections.sort(list, Collections.reverseOrder());
+ Comparator cmp = Collections.reverseOrder();
+ Collections.sort(list, cmp);
Foo[] golden = { new Foo(3), new Foo(2), new Foo(1) };
List goldenList = Arrays.asList(golden);
if (!list.equals(goldenList))
throw new Exception(list.toString());
+
+ Comparator clone = serialClone(cmp);
+ List list2 = Arrays.asList(a);
+ Collections.sort(list2, clone);
+ if (!list2.equals(goldenList))
+ throw new Exception(list.toString());
}
}
diff --git a/jdk/test/java/util/ComparatorsTest.java b/jdk/test/java/util/ComparatorsTest.java
new file mode 100644
index 0000000..1640c2d
--- /dev/null
+++ b/jdk/test/java/util/ComparatorsTest.java
@@ -0,0 +1,353 @@
+/*
+ * Copyright (c) 2012, 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.
+ *
+ * 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.
+ */
+
+/*
+ * @test
+ * @bug 8001667
+ * @run testng ComparatorsTest
+ */
+
+import java.util.Comparator;
+import java.util.Comparators;
+import java.util.AbstractMap;
+import java.util.Map;
+import org.testng.annotations.Test;
+
+import java.util.function.Function;
+import java.util.function.ToIntFunction;
+import java.util.function.ToLongFunction;
+import java.util.function.ToDoubleFunction;
+
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertTrue;
+import static org.testng.Assert.assertSame;
+
+/**
+ * Unit tests for helper methods in Comparators
+ */
+@Test(groups = "unit")
+public class ComparatorsTest {
+ private static class Thing {
+ public final int intField;
+ public final long longField;
+ public final double doubleField;
+ public final String stringField;
+
+ private Thing(int intField, long longField, double doubleField, String stringField) {
+ this.intField = intField;
+ this.longField = longField;
+ this.doubleField = doubleField;
+ this.stringField = stringField;
+ }
+
+ public int getIntField() {
+ return intField;
+ }
+
+ public long getLongField() {
+ return longField;
+ }
+
+ public double getDoubleField() {
+ return doubleField;
+ }
+
+ public String getStringField() {
+ return stringField;
+ }
+ }
+
+ private final int[] intValues = { -2, -2, -1, -1, 0, 0, 1, 1, 2, 2 };
+ private final long[] longValues = { -2, -2, -1, -1, 0, 0, 1, 1, 2, 2 };
+ private final double[] doubleValues = { -2, -2, -1, -1, 0, 0, 1, 1, 2, 2 };
+ private final String[] stringValues = { "a", "a", "b", "b", "c", "c", "d", "d", "e", "e" };
+ private final int[] comparisons = { 0, -1, 0, -1, 0, -1, 0, -1, 0 };
+
+ private<T> void assertComparisons(T[] things, Comparator<T> comp, int[] comparisons) {
+ for (int i=0; i<comparisons.length; i++) {
+ assertEquals(comparisons.length + 1, things.length);
+ assertEquals(comparisons[i], comp.compare(things[i], things[i+1]));
+ assertEquals(-comparisons[i], comp.compare(things[i+1], things[i]));
+ }
+ }
+
+ public void testIntComparator() {
+ Thing[] things = new Thing[intValues.length];
+ for (int i=0; i<intValues.length; i++)
+ things[i] = new Thing(intValues[i], 0L, 0.0, null);
+ Comparator<Thing> comp = Comparators.comparing(new ToIntFunction<ComparatorsTest.Thing>() {
+ @Override
+ public int applyAsInt(Thing thing) {
+ return thing.getIntField();
+ }
+ });
+
+ assertComparisons(things, comp, comparisons);
+ }
+
+ public void testLongComparator() {
+ Thing[] things = new Thing[longValues.length];
+ for (int i=0; i<longValues.length; i++)
+ things[i] = new Thing(0, longValues[i], 0.0, null);
+ Comparator<Thing> comp = Comparators.comparing(new ToLongFunction<ComparatorsTest.Thing>() {
+ @Override
+ public long applyAsLong(Thing thing) {
+ return thing.getLongField();
+ }
+ });
+
+ assertComparisons(things, comp, comparisons);
+ }
+
+ public void testDoubleComparator() {
+ Thing[] things = new Thing[doubleValues.length];
+ for (int i=0; i<doubleValues.length; i++)
+ things[i] = new Thing(0, 0L, doubleValues[i], null);
+ Comparator<Thing> comp = Comparators.comparing(new ToDoubleFunction<ComparatorsTest.Thing>() {
+ @Override
+ public double applyAsDouble(Thing thing) {
+ return thing.getDoubleField();
+ }
+ });
+
+ assertComparisons(things, comp, comparisons);
+ }
+
+ public void testComparing() {
+ Thing[] things = new Thing[doubleValues.length];
+ for (int i=0; i<doubleValues.length; i++)
+ things[i] = new Thing(0, 0L, 0.0, stringValues[i]);
+ Comparator<Thing> comp = Comparators.comparing(new Function<Thing, String>() {
+ @Override
+ public String apply(Thing thing) {
+ return thing.getStringField();
+ }
+ });
+
+ assertComparisons(things, comp, comparisons);
+ }
+
+ public void testNaturalOrderComparator() {
+ Comparator<String> comp = Comparators.naturalOrder();
+
+ assertComparisons(stringValues, comp, comparisons);
+ }
+
+ public void testReverseComparator() {
+ Comparator<String> cmpr = Comparators.reverseOrder();
+ Comparator<String> cmp = cmpr.reverseOrder();
+
+ assertEquals(cmp.reverseOrder(), cmpr);
+ assertEquals(0, cmp.compare("a", "a"));
+ assertEquals(0, cmpr.compare("a", "a"));
+ assertTrue(cmp.compare("a", "b") < 0);
+ assertTrue(cmpr.compare("a", "b") > 0);
+ assertTrue(cmp.compare("b", "a") > 0);
+ assertTrue(cmpr.compare("b", "a") < 0);
+ }
+
+ public void testReverseComparator2() {
+ Comparator<String> cmp = (s1, s2) -> s1.length() - s2.length();
+ Comparator<String> cmpr = cmp.reverseOrder();
+
+ assertEquals(cmpr.reverseOrder(), cmp);
+ assertEquals(0, cmp.compare("abc", "def"));
+ assertEquals(0, cmpr.compare("abc", "def"));
+ assertTrue(cmp.compare("abcd", "def") > 0);
+ assertTrue(cmpr.compare("abcd", "def") < 0);
+ assertTrue(cmp.compare("abc", "defg") < 0);
+ assertTrue(cmpr.compare("abc", "defg") > 0);
+ }
+
+ @Test(expectedExceptions=NullPointerException.class)
+ public void testReverseComparatorNPE() {
+ Comparator<String> cmp = Comparators.reverseOrder(null);
+ }
+
+ public void testComposeComparator() {
+ // Longer string in front
+ Comparator<String> first = (s1, s2) -> s2.length() - s1.length();
+ Comparator<String> second = Comparators.naturalOrder();
+ Comparator<String> composed = Comparators.compose(first, second);
+
+ assertTrue(composed.compare("abcdefg", "abcdef") < 0);
+ assertTrue(composed.compare("abcdef", "abcdefg") > 0);
+ assertTrue(composed.compare("abcdef", "abcdef") == 0);
+ assertTrue(composed.compare("abcdef", "ghijkl") < 0);
+ assertTrue(composed.compare("ghijkl", "abcdefg") > 0);
+ }
+
+ private <K, V> void assertPairComparison(K k1, V v1, K k2, V v2,
+ Comparator<Map.Entry<K, V>> ck,
+ Comparator<Map.Entry<K, V>> cv) {
+ final Map.Entry<K, V> p11 = new AbstractMap.SimpleImmutableEntry<>(k1, v1);
+ final Map.Entry<K, V> p12 = new AbstractMap.SimpleImmutableEntry<>(k1, v2);
+ final Map.Entry<K, V> p21 = new AbstractMap.SimpleImmutableEntry<>(k2, v1);
+ final Map.Entry<K, V> p22 = new AbstractMap.SimpleImmutableEntry<>(k2, v2);
+
+ assertTrue(ck.compare(p11, p11) == 0);
+ assertTrue(ck.compare(p12, p11) == 0);
+ assertTrue(ck.compare(p11, p12) == 0);
+ assertTrue(ck.compare(p12, p22) < 0);
+ assertTrue(ck.compare(p12, p21) < 0);
+ assertTrue(ck.compare(p21, p11) > 0);
+ assertTrue(ck.compare(p21, p12) > 0);
+
+ assertTrue(cv.compare(p11, p11) == 0);
+ assertTrue(cv.compare(p12, p11) > 0);
+ assertTrue(cv.compare(p11, p12) < 0);
+ assertTrue(cv.compare(p12, p22) == 0);
+ assertTrue(cv.compare(p12, p21) > 0);
+ assertTrue(cv.compare(p21, p11) == 0);
+ assertTrue(cv.compare(p21, p12) < 0);
+
+ Comparator<Map.Entry<K, V>> cmp = Comparators.compose(ck, cv);
+ assertTrue(cmp.compare(p11, p11) == 0);
+ assertTrue(cmp.compare(p12, p11) > 0);
+ assertTrue(cmp.compare(p11, p12) < 0);
+ assertTrue(cmp.compare(p12, p22) < 0);
+ assertTrue(cmp.compare(p12, p21) < 0);
+ assertTrue(cmp.compare(p21, p11) > 0);
+ assertTrue(cmp.compare(p21, p12) > 0);
+
+ cmp = Comparators.compose(cv, ck);
+ assertTrue(cmp.compare(p11, p11) == 0);
+ assertTrue(cmp.compare(p12, p11) > 0);
+ assertTrue(cmp.compare(p11, p12) < 0);
+ assertTrue(cmp.compare(p12, p22) < 0);
+ assertTrue(cmp.compare(p12, p21) > 0);
+ assertTrue(cmp.compare(p21, p11) > 0);
+ assertTrue(cmp.compare(p21, p12) < 0);
+ }
+
+ public void testKVComparatorable() {
+ assertPairComparison(1, "ABC", 2, "XYZ",
+ Comparators.<Integer, String>naturalOrderKeys(),
+ Comparators.<Integer, String>naturalOrderValues());
+ }
+
+ private static class People {
+ final String firstName;
+ final String lastName;
+ final int age;
+
+ People(String first, String last, int age) {
+ firstName = first;
+ lastName = last;
+ this.age = age;
+ }
+
+ String getFirstName() { return firstName; }
+ String getLastName() { return lastName; }
+ int getAge() { return age; }
+ long getAgeAsLong() { return (long) age; };
+ double getAgeAsDouble() { return (double) age; };
+ }
+
+ private final People people[] = {
+ new People("John", "Doe", 34),
+ new People("Mary", "Doe", 30),
+ new People("Maria", "Doe", 14),
+ new People("Jonah", "Doe", 10),
+ new People("John", "Cook", 54),
+ new People("Mary", "Cook", 50),
+ };
+
+ public void testKVComparators() {
+ // Comparator<People> cmp = Comparators.naturalOrder(); // Should fail to compiler as People is not comparable
+ // We can use simple comparator, but those have been tested above.
+ // Thus choose to do compose for some level of interation.
+ Comparator<People> cmp1 = Comparators.comparing((Function<People, String>) People::getFirstName);
+ Comparator<People> cmp2 = Comparators.comparing((Function<People, String>) People::getLastName);
+ Comparator<People> cmp = Comparators.compose(cmp1, cmp2);
+
+ assertPairComparison(people[0], people[0], people[1], people[1],
+ Comparators.<People, People>byKey(cmp),
+ Comparators.<People, People>byValue(cmp));
+
+ }
+
+ private <T> void assertComparison(Comparator<T> cmp, T less, T greater) {
+ assertTrue(cmp.compare(less, greater) < 0, "less");
+ assertTrue(cmp.compare(less, less) == 0, "equal");
+ assertTrue(cmp.compare(greater, less) > 0, "greater");
+ }
+
+ public void testComparatorDefaultMethods() {
+ Comparator<People> cmp = Comparators.comparing((Function<People, String>) People::getFirstName);
+ Comparator<People> cmp2 = Comparators.comparing((Function<People, String>) People::getLastName);
+ // reverseOrder
+ assertComparison(cmp.reverseOrder(), people[1], people[0]);
+ // thenComparing(Comparator)
+ assertComparison(cmp.thenComparing(cmp2), people[0], people[1]);
+ assertComparison(cmp.thenComparing(cmp2), people[4], people[0]);
+ // thenComparing(Function)
+ assertComparison(cmp.thenComparing(People::getLastName), people[0], people[1]);
+ assertComparison(cmp.thenComparing(People::getLastName), people[4], people[0]);
+ // thenComparing(ToIntFunction)
+ assertComparison(cmp.thenComparing(People::getAge), people[0], people[1]);
+ assertComparison(cmp.thenComparing(People::getAge), people[1], people[5]);
+ // thenComparing(ToLongFunction)
+ assertComparison(cmp.thenComparing(People::getAgeAsLong), people[0], people[1]);
+ assertComparison(cmp.thenComparing(People::getAgeAsLong), people[1], people[5]);
+ // thenComparing(ToDoubleFunction)
+ assertComparison(cmp.thenComparing(People::getAgeAsDouble), people[0], people[1]);
+ assertComparison(cmp.thenComparing(People::getAgeAsDouble), people[1], people[5]);
+ }
+
+ public void testGreaterOf() {
+ // lesser
+ assertSame(Comparators.greaterOf(Comparators.comparing(
+ (Function<People, String>) People::getFirstName))
+ .apply(people[0], people[1]),
+ people[1]);
+ // euqal
+ assertSame(Comparators.greaterOf(Comparators.comparing(
+ (Function<People, String>) People::getLastName))
+ .apply(people[0], people[1]),
+ people[0]);
+ // greater
+ assertSame(Comparators.greaterOf(Comparators.comparing(
+ (ToIntFunction<People>) People::getAge))
+ .apply(people[0], people[1]),
+ people[0]);
+ }
+
+ public void testLesserOf() {
+ // lesser
+ assertSame(Comparators.lesserOf(Comparators.comparing(
+ (Function<People, String>) People::getFirstName))
+ .apply(people[0], people[1]),
+ people[0]);
+ // euqal
+ assertSame(Comparators.lesserOf(Comparators.comparing(
+ (Function<People, String>) People::getLastName))
+ .apply(people[0], people[1]),
+ people[0]);
+ // greater
+ assertSame(Comparators.lesserOf(Comparators.comparing(
+ (ToIntFunction<People>) People::getAge))
+ .apply(people[0], people[1]),
+ people[1]);
+ }
+}
\ No newline at end of file
