--- a/jdk/src/share/classes/java/util/stream/Collectors.java Tue Aug 06 16:01:39 2013 -0700
+++ b/jdk/src/share/classes/java/util/stream/Collectors.java Fri Jun 28 16:26:54 2013 -0400
@@ -27,6 +27,7 @@
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.ArrayList;
+import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
@@ -39,14 +40,16 @@
import java.util.List;
import java.util.LongSummaryStatistics;
import java.util.Map;
-import java.util.NoSuchElementException;
import java.util.Objects;
+import java.util.Optional;
import java.util.Set;
import java.util.StringJoiner;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
+import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.BinaryOperator;
+import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
@@ -64,20 +67,21 @@
* mutable reduction tasks:
*
* <pre>{@code
- * // Accumulate elements into a List
- * List<Person> list = people.collect(Collectors.toList());
+ * // Accumulate names into a List
+ * List<String> list = people.stream().map(Person::getName).collect(Collectors.toList());
*
- * // Accumulate elements into a TreeSet
- * List<Person> list = people.collect(Collectors.toCollection(TreeSet::new));
+ * // Accumulate names into a TreeSet
+ * Set<String> list = people.stream().map(Person::getName).collect(Collectors.toCollection(TreeSet::new));
*
* // Convert elements to strings and concatenate them, separated by commas
- * String joined = stream.map(Object::toString)
- * .collect(Collectors.toStringJoiner(", "))
- * .toString();
+ * String joined = things.stream()
+ * .map(Object::toString)
+ * .collect(Collectors.joining(", "));
*
* // Find highest-paid employee
* Employee highestPaid = employees.stream()
- * .collect(Collectors.maxBy(Comparator.comparing(Employee::getSalary)));
+ * .collect(Collectors.maxBy(Comparator.comparing(Employee::getSalary)))
+ * .get();
*
* // Group employees by department
* Map<Department, List<Employee>> byDept
@@ -85,7 +89,7 @@
* .collect(Collectors.groupingBy(Employee::getDepartment));
*
* // Find highest-paid employee by department
- * Map<Department, Employee> highestPaidByDept
+ * Map<Department, Optional<Employee>> highestPaidByDept
* = employees.stream()
* .collect(Collectors.groupingBy(Employee::getDepartment,
* Collectors.maxBy(Comparator.comparing(Employee::getSalary))));
@@ -93,7 +97,7 @@
* // Partition students into passing and failing
* Map<Boolean, List<Student>> passingFailing =
* students.stream()
- * .collect(Collectors.partitioningBy(s -> s.getGrade() >= PASS_THRESHOLD);
+ * .collect(Collectors.partitioningBy(s -> s.getGrade() >= PASS_THRESHOLD));
*
* }</pre>
*
@@ -103,15 +107,19 @@
*/
public final class Collectors {
- private static final Set<Collector.Characteristics> CH_CONCURRENT
+ static final Set<Collector.Characteristics> CH_CONCURRENT_ID
= Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.CONCURRENT,
- Collector.Characteristics.STRICTLY_MUTATIVE,
+ Collector.Characteristics.UNORDERED,
+ Collector.Characteristics.IDENTITY_FINISH));
+ static final Set<Collector.Characteristics> CH_CONCURRENT_NOID
+ = Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.CONCURRENT,
Collector.Characteristics.UNORDERED));
- private static final Set<Collector.Characteristics> CH_STRICT
- = Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.STRICTLY_MUTATIVE));
- private static final Set<Collector.Characteristics> CH_STRICT_UNORDERED
- = Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.STRICTLY_MUTATIVE,
- Collector.Characteristics.UNORDERED));
+ static final Set<Collector.Characteristics> CH_ID
+ = Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.IDENTITY_FINISH));
+ static final Set<Collector.Characteristics> CH_UNORDERED_ID
+ = Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.UNORDERED,
+ Collector.Characteristics.IDENTITY_FINISH));
+ static final Set<Collector.Characteristics> CH_NOID = Collections.emptySet();
private Collectors() { }
@@ -124,88 +132,64 @@
*
* @param <T> the type of input arguments to the merge function
* @return a merge function which always throw {@code IllegalStateException}
- *
- * @see #firstWinsMerger()
- * @see #lastWinsMerger()
*/
- public static <T> BinaryOperator<T> throwingMerger() {
+ private static <T> BinaryOperator<T> throwingMerger() {
return (u,v) -> { throw new IllegalStateException(String.format("Duplicate key %s", u)); };
}
/**
- * Returns a merge function, suitable for use in
- * {@link Map#merge(Object, Object, BiFunction) Map.merge()} or
- * {@link #toMap(Function, Function, BinaryOperator) toMap()},
- * which implements a "first wins" policy.
- *
- * @param <T> the type of input arguments to the merge function
- * @return a merge function which always returns its first argument
- * @see #lastWinsMerger()
- * @see #throwingMerger()
- */
- public static <T> BinaryOperator<T> firstWinsMerger() {
- return (u,v) -> u;
- }
-
- /**
- * Returns a merge function, suitable for use in
- * {@link Map#merge(Object, Object, BiFunction) Map.merge()} or
- * {@link #toMap(Function, Function, BinaryOperator) toMap()},
- * which implements a "last wins" policy.
- *
- * @param <T> the type of input arguments to the merge function
- * @return a merge function which always returns its second argument
- * @see #firstWinsMerger()
- * @see #throwingMerger()
- */
- public static <T> BinaryOperator<T> lastWinsMerger() {
- return (u,v) -> v;
- }
-
- /**
* Simple implementation class for {@code Collector}.
*
* @param <T> the type of elements to be collected
* @param <R> the type of the result
*/
- private static final class CollectorImpl<T, R> implements Collector<T,R> {
- private final Supplier<R> resultSupplier;
- private final BiFunction<R, T, R> accumulator;
- private final BinaryOperator<R> combiner;
+ static class CollectorImpl<T, A, R> implements Collector<T, A, R> {
+ private final Supplier<A> supplier;
+ private final BiConsumer<A, T> accumulator;
+ private final BinaryOperator<A> combiner;
+ private final Function<A, R> finisher;
private final Set<Characteristics> characteristics;
- CollectorImpl(Supplier<R> resultSupplier,
- BiFunction<R, T, R> accumulator,
- BinaryOperator<R> combiner,
+ CollectorImpl(Supplier<A> supplier,
+ BiConsumer<A, T> accumulator,
+ BinaryOperator<A> combiner,
+ Function<A,R> finisher,
Set<Characteristics> characteristics) {
- this.resultSupplier = resultSupplier;
+ this.supplier = supplier;
this.accumulator = accumulator;
this.combiner = combiner;
+ this.finisher = finisher;
this.characteristics = characteristics;
}
- CollectorImpl(Supplier<R> resultSupplier,
- BiFunction<R, T, R> accumulator,
- BinaryOperator<R> combiner) {
- this(resultSupplier, accumulator, combiner, Collections.emptySet());
+ CollectorImpl(Supplier<A> supplier,
+ BiConsumer<A, T> accumulator,
+ BinaryOperator<A> combiner,
+ Set<Characteristics> characteristics) {
+ this(supplier, accumulator, combiner, i -> (R) i, characteristics);
}
@Override
- public BiFunction<R, T, R> accumulator() {
+ public BiConsumer<A, T> accumulator() {
return accumulator;
}
@Override
- public Supplier<R> resultSupplier() {
- return resultSupplier;
+ public Supplier<A> supplier() {
+ return supplier;
}
@Override
- public BinaryOperator<R> combiner() {
+ public BinaryOperator<A> combiner() {
return combiner;
}
@Override
+ public Function<A, R> finisher() {
+ return finisher;
+ }
+
+ @Override
public Set<Characteristics> characteristics() {
return characteristics;
}
@@ -224,11 +208,10 @@
* {@code Collection}, in encounter order
*/
public static <T, C extends Collection<T>>
- Collector<T, C> toCollection(Supplier<C> collectionFactory) {
- return new CollectorImpl<>(collectionFactory,
- (r, t) -> { r.add(t); return r; },
+ Collector<T, ?, C> toCollection(Supplier<C> collectionFactory) {
+ return new CollectorImpl<>(collectionFactory, Collection::add,
(r1, r2) -> { r1.addAll(r2); return r1; },
- CH_STRICT);
+ CH_ID);
}
/**
@@ -241,36 +224,10 @@
* {@code List}, in encounter order
*/
public static <T>
- Collector<T, List<T>> toList() {
- BiFunction<List<T>, T, List<T>> accumulator = (list, t) -> {
- switch (list.size()) {
- case 0:
- return Collections.singletonList(t);
- case 1:
- List<T> newList = new ArrayList<>();
- newList.add(list.get(0));
- newList.add(t);
- return newList;
- default:
- list.add(t);
- return list;
- }
- };
- BinaryOperator<List<T>> combiner = (left, right) -> {
- switch (left.size()) {
- case 0:
- return right;
- case 1:
- List<T> newList = new ArrayList<>(left.size() + right.size());
- newList.addAll(left);
- newList.addAll(right);
- return newList;
- default:
- left.addAll(right);
- return left;
- }
- };
- return new CollectorImpl<>(Collections::emptyList, accumulator, combiner);
+ Collector<T, ?, List<T>> toList() {
+ return new CollectorImpl<>((Supplier<List<T>>) ArrayList::new, List::add,
+ (left, right) -> { left.addAll(right); return left; },
+ CH_ID);
}
/**
@@ -286,44 +243,58 @@
* {@code Set}
*/
public static <T>
- Collector<T, Set<T>> toSet() {
- return new CollectorImpl<>((Supplier<Set<T>>) HashSet::new,
- (r, t) -> { r.add(t); return r; },
- (r1, r2) -> { r1.addAll(r2); return r1; },
- CH_STRICT_UNORDERED);
+ Collector<T, ?, Set<T>> toSet() {
+ return new CollectorImpl<>((Supplier<Set<T>>) HashSet::new, Set::add,
+ (left, right) -> { left.addAll(right); return left; },
+ CH_UNORDERED_ID);
}
/**
* Returns a {@code Collector} that concatenates the input elements into a
- * new {@link StringBuilder}.
+ * {@code String}, in encounter order.
*
- * @return a {@code Collector} which collects String elements into a
- * {@code StringBuilder}, in encounter order
+ * @return a {@code Collector} that concatenates the input elements into a
+ * {@code String}, in encounter order
*/
- public static Collector<String, StringBuilder> toStringBuilder() {
- return new CollectorImpl<>(StringBuilder::new,
- (r, t) -> { r.append(t); return r; },
- (r1, r2) -> { r1.append(r2); return r1; },
- CH_STRICT);
+ public static Collector<CharSequence, ?, String> joining() {
+ return new CollectorImpl<CharSequence, StringBuilder, String>(
+ StringBuilder::new, StringBuilder::append,
+ (r1, r2) -> { r1.append(r2); return r1; },
+ StringBuilder::toString, CH_NOID);
}
/**
- * Returns a {@code Collector} that concatenates the input elements into a
- * new {@link StringJoiner}, using the specified delimiter.
+ * Returns a {@code Collector} that concatenates the input elements,
+ * separated by the specified delimiter, in encounter order.
*
* @param delimiter the delimiter to be used between each element
- * @return A {@code Collector} which collects String elements into a
- * {@code StringJoiner}, in encounter order
+ * @return A {@code Collector} which concatenates CharSequence elements,
+ * separated by the specified delimiter, in encounter order
*/
- public static Collector<CharSequence, StringJoiner> toStringJoiner(CharSequence delimiter) {
- BinaryOperator<StringJoiner> merger = (sj, other) -> {
- if (other.length() > 0)
- sj.add(other.toString());
- return sj;
- };
- return new CollectorImpl<>(() -> new StringJoiner(delimiter),
- (r, t) -> { r.add(t); return r; },
- merger, CH_STRICT);
+ public static Collector<CharSequence, ?, String> joining(CharSequence delimiter) {
+ return joining(delimiter, "", "");
+ }
+
+ /**
+ * Returns a {@code Collector} that concatenates the input elements,
+ * separated by the specified delimiter, with the specified prefix and
+ * suffix, in encounter order.
+ *
+ * @param delimiter the delimiter to be used between each element
+ * @param prefix the sequence of characters to be used at the beginning
+ * of the joined result
+ * @param suffix the sequence of characters to be used at the end
+ * of the joined result
+ * @return A {@code Collector} which concatenates CharSequence elements,
+ * separated by the specified delimiter, in encounter order
+ */
+ public static Collector<CharSequence, ?, String> joining(CharSequence delimiter,
+ CharSequence prefix,
+ CharSequence suffix) {
+ return new CollectorImpl<>(
+ () -> new StringJoiner(delimiter, prefix, suffix),
+ StringJoiner::add, StringJoiner::merge,
+ StringJoiner::toString, CH_NOID);
}
/**
@@ -348,12 +319,13 @@
}
/**
- * Adapts a {@code Collector<U,R>} to a {@code Collector<T,R>} by applying
- * a mapping function to each input element before accumulation.
+ * Adapts a {@code Collector} accepting elements of type {@code U} to one
+ * accepting elements of type {@code T} by applying a mapping function to
+ * each input element before accumulation.
*
* @apiNote
* The {@code mapping()} collectors are most useful when used in a
- * multi-level reduction, downstream of {@code groupingBy} or
+ * multi-level reduction, such as downstream of a {@code groupingBy} or
* {@code partitioningBy}. For example, given a stream of
* {@code Person}, to accumulate the set of last names in each city:
* <pre>{@code
@@ -364,23 +336,27 @@
*
* @param <T> the type of the input elements
* @param <U> type of elements accepted by downstream collector
+ * @param <A> intermediate accumulation type of the downstream collector
* @param <R> result type of collector
* @param mapper a function to be applied to the input elements
* @param downstream a collector which will accept mapped values
* @return a collector which applies the mapping function to the input
* elements and provides the mapped results to the downstream collector
*/
- public static <T, U, R> Collector<T, R>
- mapping(Function<? super T, ? extends U> mapper, Collector<? super U, R> downstream) {
- BiFunction<R, ? super U, R> downstreamAccumulator = downstream.accumulator();
- return new CollectorImpl<>(downstream.resultSupplier(),
- (r, t) -> downstreamAccumulator.apply(r, mapper.apply(t)),
- downstream.combiner(), downstream.characteristics());
+ public static <T, U, A, R>
+ Collector<T, ?, R> mapping(Function<? super T, ? extends U> mapper,
+ Collector<? super U, A, R> downstream) {
+ BiConsumer<A, ? super U> downstreamAccumulator = downstream.accumulator();
+ return new CollectorImpl<>(downstream.supplier(),
+ (r, t) -> downstreamAccumulator.accept(r, mapper.apply(t)),
+ downstream.combiner(), downstream.finisher(),
+ downstream.characteristics());
}
/**
- * Returns a {@code Collector<T, Long>} that counts the number of input
- * elements.
+ * Returns a {@code Collector} accepting elements of type {@code T} that
+ * counts the number of input elements. If no elements are present, the
+ * result is 0.
*
* @implSpec
* This produces a result equivalent to:
@@ -391,14 +367,14 @@
* @param <T> the type of the input elements
* @return a {@code Collector} that counts the input elements
*/
- public static <T> Collector<T, Long>
+ public static <T> Collector<T, ?, Long>
counting() {
return reducing(0L, e -> 1L, Long::sum);
}
/**
- * Returns a {@code Collector<T, T>} that produces the minimal element
- * according to a given {@code Comparator}.
+ * Returns a {@code Collector} that produces the minimal element according
+ * to a given {@code Comparator}, described as an {@code Optional<T>}.
*
* @implSpec
* This produces a result equivalent to:
@@ -410,14 +386,14 @@
* @param comparator a {@code Comparator} for comparing elements
* @return a {@code Collector} that produces the minimal value
*/
- public static <T> Collector<T, T>
+ public static <T> Collector<T, ?, Optional<T>>
minBy(Comparator<? super T> comparator) {
return reducing(BinaryOperator.minBy(comparator));
}
/**
- * Returns a {@code Collector<T, T>} that produces the maximal element
- * according to a given {@code Comparator}.
+ * Returns a {@code Collector} that produces the maximal element according
+ * to a given {@code Comparator}, described as an {@code Optional<T>}.
*
* @implSpec
* This produces a result equivalent to:
@@ -429,39 +405,143 @@
* @param comparator a {@code Comparator} for comparing elements
* @return a {@code Collector} that produces the maximal value
*/
- public static <T> Collector<T, T>
+ public static <T> Collector<T, ?, Optional<T>>
maxBy(Comparator<? super T> comparator) {
return reducing(BinaryOperator.maxBy(comparator));
}
/**
- * Returns a {@code Collector<T, Long>} that produces the sum of a
- * long-valued function applied to the input element.
+ * Returns a {@code Collector} that produces the sum of a integer-valued
+ * function applied to the input elements. If no elements are present,
+ * the result is 0.
+ *
+ * @param <T> the type of the input elements
+ * @param mapper a function extracting the property to be summed
+ * @return a {@code Collector} that produces the sum of a derived property
+ */
+ public static <T> Collector<T, ?, Integer>
+ summingInt(ToIntFunction<? super T> mapper) {
+ return new CollectorImpl<T, int[], Integer>(
+ () -> new int[1],
+ (a, t) -> { a[0] += mapper.applyAsInt(t); },
+ (a, b) -> { a[0] += b[0]; return a; },
+ a -> a[0], CH_NOID);
+ }
+
+ /**
+ * Returns a {@code Collector} that produces the sum of a long-valued
+ * function applied to the input elements. If no elements are present,
+ * the result is 0.
*
- * @implSpec
- * This produces a result equivalent to:
- * <pre>{@code
- * reducing(0L, mapper, Long::sum)
- * }</pre>
+ * @param <T> the type of the input elements
+ * @param mapper a function extracting the property to be summed
+ * @return a {@code Collector} that produces the sum of a derived property
+ */
+ public static <T> Collector<T, ?, Long>
+ summingLong(ToLongFunction<? super T> mapper) {
+ return new CollectorImpl<T, long[], Long>(
+ () -> new long[1],
+ (a, t) -> { a[0] += mapper.applyAsLong(t); },
+ (a, b) -> { a[0] += b[0]; return a; },
+ a -> a[0], CH_NOID);
+ }
+
+ /**
+ * Returns a {@code Collector} that produces the sum of a double-valued
+ * function applied to the input elements. If no elements are present,
+ * the result is 0.
+ *
+ * <p>The sum returned can vary depending upon the order in which
+ * values are recorded, due to accumulated rounding error in
+ * addition of values of differing magnitudes. Values sorted by increasing
+ * absolute magnitude tend to yield more accurate results. If any recorded
+ * value is a {@code NaN} or the sum is at any point a {@code NaN} then the
+ * sum will be {@code NaN}.
*
* @param <T> the type of the input elements
* @param mapper a function extracting the property to be summed
* @return a {@code Collector} that produces the sum of a derived property
*/
- public static <T> Collector<T, Long>
- sumBy(Function<? super T, Long> mapper) {
- return reducing(0L, mapper, Long::sum);
+ public static <T> Collector<T, ?, Double>
+ summingDouble(ToDoubleFunction<? super T> mapper) {
+ return new CollectorImpl<T, double[], Double>(
+ () -> new double[1],
+ (a, t) -> { a[0] += mapper.applyAsDouble(t); },
+ (a, b) -> { a[0] += b[0]; return a; },
+ a -> a[0], CH_NOID);
+ }
+
+ /**
+ * Returns a {@code Collector} that produces the arithmetic mean of an integer-valued
+ * function applied to the input elements. If no elements are present,
+ * the result is 0.
+ *
+ * @param <T> the type of the input elements
+ * @param mapper a function extracting the property to be summed
+ * @return a {@code Collector} that produces the sum of a derived property
+ */
+ public static <T> Collector<T, ?, Double>
+ averagingInt(ToIntFunction<? super T> mapper) {
+ return new CollectorImpl<T, long[], Double>(
+ () -> new long[2],
+ (a, t) -> { a[0] += mapper.applyAsInt(t); a[1]++; },
+ (a, b) -> { a[0] += b[0]; a[1] += b[1]; return a; },
+ a -> (a[1] == 0) ? 0.0d : (double) a[0] / a[1], CH_NOID);
}
/**
- * Returns a {@code Collector<T,T>} which performs a reduction of its
- * input elements under a specified {@code BinaryOperator}.
+ * Returns a {@code Collector} that produces the arithmetic mean of a long-valued
+ * function applied to the input elements. If no elements are present,
+ * the result is 0.
+ *
+ * @param <T> the type of the input elements
+ * @param mapper a function extracting the property to be summed
+ * @return a {@code Collector} that produces the sum of a derived property
+ */
+ public static <T> Collector<T, ?, Double>
+ averagingLong(ToLongFunction<? super T> mapper) {
+ return new CollectorImpl<T, long[], Double>(
+ () -> new long[2],
+ (a, t) -> { a[0] += mapper.applyAsLong(t); a[1]++; },
+ (a, b) -> { a[0] += b[0]; a[1] += b[1]; return a; },
+ a -> (a[1] == 0) ? 0.0d : (double) a[0] / a[1], CH_NOID);
+ }
+
+ /**
+ * Returns a {@code Collector} that produces the arithmetic mean of a double-valued
+ * function applied to the input elements. If no elements are present,
+ * the result is 0.
+ *
+ * <p>The average returned can vary depending upon the order in which
+ * values are recorded, due to accumulated rounding error in
+ * addition of values of differing magnitudes. Values sorted by increasing
+ * absolute magnitude tend to yield more accurate results. If any recorded
+ * value is a {@code NaN} or the sum is at any point a {@code NaN} then the
+ * average will be {@code NaN}.
+ *
+ * @param <T> the type of the input elements
+ * @param mapper a function extracting the property to be summed
+ * @return a {@code Collector} that produces the sum of a derived property
+ */
+ public static <T> Collector<T, ?, Double>
+ averagingDouble(ToDoubleFunction<? super T> mapper) {
+ return new CollectorImpl<T, double[], Double>(
+ () -> new double[2],
+ (a, t) -> { a[0] += mapper.applyAsDouble(t); a[1]++; },
+ (a, b) -> { a[0] += b[0]; a[1] += b[1]; return a; },
+ a -> (a[1] == 0) ? 0.0d : a[0] / a[1], CH_NOID);
+ }
+
+ /**
+ * Returns a {@code Collector} which performs a reduction of its
+ * input elements under a specified {@code BinaryOperator} using the
+ * provided identity.
*
* @apiNote
* The {@code reducing()} collectors are most useful when used in a
* multi-level reduction, downstream of {@code groupingBy} or
* {@code partitioningBy}. To perform a simple reduction on a stream,
- * use {@link Stream#reduce(BinaryOperator)} instead.
+ * use {@link Stream#reduce(Object, BinaryOperator)}} instead.
*
* @param <T> element type for the input and output of the reduction
* @param identity the identity value for the reduction (also, the value
@@ -472,14 +552,25 @@
* @see #reducing(BinaryOperator)
* @see #reducing(Object, Function, BinaryOperator)
*/
- public static <T> Collector<T, T>
+ public static <T> Collector<T, ?, T>
reducing(T identity, BinaryOperator<T> op) {
- return new CollectorImpl<>(() -> identity, (r, t) -> (r == null ? t : op.apply(r, t)), op);
+ return new CollectorImpl<>(
+ boxSupplier(identity),
+ (a, t) -> { a[0] = op.apply(a[0], t); },
+ (a, b) -> { a[0] = op.apply(a[0], b[0]); return a; },
+ a -> a[0],
+ CH_NOID);
+ }
+
+ @SuppressWarnings("unchecked")
+ private static <T> Supplier<T[]> boxSupplier(T identity) {
+ return () -> (T[]) new Object[] { identity };
}
/**
- * Returns a {@code Collector<T,T>} which performs a reduction of its
- * input elements under a specified {@code BinaryOperator}.
+ * Returns a {@code Collector} which performs a reduction of its
+ * input elements under a specified {@code BinaryOperator}. The result
+ * is described as an {@code Optional<T>}.
*
* @apiNote
* The {@code reducing()} collectors are most useful when used in a
@@ -491,15 +582,8 @@
* person in each city:
* <pre>{@code
* Comparator<Person> byHeight = Comparator.comparing(Person::getHeight);
- * BinaryOperator<Person> tallerOf = BinaryOperator.greaterOf(byHeight);
* Map<City, Person> tallestByCity
- * = people.stream().collect(groupingBy(Person::getCity, reducing(tallerOf)));
- * }</pre>
- *
- * @implSpec
- * The default implementation is equivalent to:
- * <pre>{@code
- * reducing(null, op);
+ * = people.stream().collect(groupingBy(Person::getCity, reducing(BinaryOperator.maxBy(byHeight))));
* }</pre>
*
* @param <T> element type for the input and output of the reduction
@@ -509,13 +593,32 @@
* @see #reducing(Object, BinaryOperator)
* @see #reducing(Object, Function, BinaryOperator)
*/
- public static <T> Collector<T, T>
+ public static <T> Collector<T, ?, Optional<T>>
reducing(BinaryOperator<T> op) {
- return reducing(null, op);
+ class OptionalBox implements Consumer<T> {
+ T value = null;
+ boolean present = false;
+
+ @Override
+ public void accept(T t) {
+ if (present) {
+ value = op.apply(value, t);
+ }
+ else {
+ value = t;
+ present = true;
+ }
+ }
+ }
+
+ return new CollectorImpl<T, OptionalBox, Optional<T>>(
+ OptionalBox::new, OptionalBox::accept,
+ (a, b) -> { if (b.present) a.accept(b.value); return a; },
+ a -> Optional.ofNullable(a.value), CH_NOID);
}
/**
- * Returns a {@code Collector<T,U>} which performs a reduction of its
+ * Returns a {@code Collector} which performs a reduction of its
* input elements under a specified mapping function and
* {@code BinaryOperator}. This is a generalization of
* {@link #reducing(Object, BinaryOperator)} which allows a transformation
@@ -524,17 +627,17 @@
* @apiNote
* The {@code reducing()} collectors are most useful when used in a
* multi-level reduction, downstream of {@code groupingBy} or
- * {@code partitioningBy}. To perform a simple reduction on a stream,
- * use {@link Stream#reduce(BinaryOperator)} instead.
+ * {@code partitioningBy}. To perform a simple map-reduce on a stream,
+ * use {@link Stream#map(Function)} and {@link Stream#reduce(Object, BinaryOperator)}
+ * instead.
*
* <p>For example, given a stream of {@code Person}, to calculate the longest
* last name of residents in each city:
* <pre>{@code
* Comparator<String> byLength = Comparator.comparing(String::length);
- * BinaryOperator<String> longerOf = BinaryOperator.greaterOf(byLength);
* Map<City, String> longestLastNameByCity
* = people.stream().collect(groupingBy(Person::getCity,
- * reducing(Person::getLastName, longerOf)));
+ * reducing(Person::getLastName, BinaryOperator.maxBy(byLength))));
* }</pre>
*
* @param <T> the type of the input elements
@@ -549,18 +652,20 @@
* @see #reducing(BinaryOperator)
*/
public static <T, U>
- Collector<T, U> reducing(U identity,
- Function<? super T, ? extends U> mapper,
- BinaryOperator<U> op) {
- return new CollectorImpl<>(() -> identity,
- (r, t) -> (r == null ? mapper.apply(t) : op.apply(r, mapper.apply(t))),
- op);
+ Collector<T, ?, U> reducing(U identity,
+ Function<? super T, ? extends U> mapper,
+ BinaryOperator<U> op) {
+ return new CollectorImpl<>(
+ boxSupplier(identity),
+ (a, t) -> { a[0] = op.apply(a[0], mapper.apply(t)); },
+ (a, b) -> { a[0] = op.apply(a[0], b[0]); return a; },
+ a -> a[0], CH_NOID);
}
/**
* Returns a {@code Collector} implementing a "group by" operation on
* input elements of type {@code T}, grouping elements according to a
- * classification function.
+ * classification function, and returning the results in a {@code Map}.
*
* <p>The classification function maps elements to some key type {@code K}.
* The collector produces a {@code Map<K, List<T>>} whose keys are the
@@ -586,9 +691,9 @@
* @see #groupingBy(Function, Supplier, Collector)
* @see #groupingByConcurrent(Function)
*/
- public static <T, K>
- Collector<T, Map<K, List<T>>> groupingBy(Function<? super T, ? extends K> classifier) {
- return groupingBy(classifier, HashMap::new, toList());
+ public static <T, K> Collector<T, ?, Map<K, List<T>>>
+ groupingBy(Function<? super T, ? extends K> classifier) {
+ return groupingBy(classifier, toList());
}
/**
@@ -615,6 +720,7 @@
*
* @param <T> the type of the input elements
* @param <K> the type of the keys
+ * @param <A> the intermediate accumulation type of the downstream collector
* @param <D> the result type of the downstream reduction
* @param classifier a classifier function mapping input elements to keys
* @param downstream a {@code Collector} implementing the downstream reduction
@@ -624,9 +730,9 @@
* @see #groupingBy(Function, Supplier, Collector)
* @see #groupingByConcurrent(Function, Collector)
*/
- public static <T, K, D>
- Collector<T, Map<K, D>> groupingBy(Function<? super T, ? extends K> classifier,
- Collector<? super T, D> downstream) {
+ public static <T, K, A, D>
+ Collector<T, ?, Map<K, D>> groupingBy(Function<? super T, ? extends K> classifier,
+ Collector<? super T, A, D> downstream) {
return groupingBy(classifier, HashMap::new, downstream);
}
@@ -653,6 +759,7 @@
*
* @param <T> the type of the input elements
* @param <K> the type of the keys
+ * @param <A> the intermediate accumulation type of the downstream collector
* @param <D> the result type of the downstream reduction
* @param <M> the type of the resulting {@code Map}
* @param classifier a classifier function mapping input elements to keys
@@ -665,25 +772,39 @@
* @see #groupingBy(Function)
* @see #groupingByConcurrent(Function, Supplier, Collector)
*/
- public static <T, K, D, M extends Map<K, D>>
- Collector<T, M> groupingBy(Function<? super T, ? extends K> classifier,
- Supplier<M> mapFactory,
- Collector<? super T, D> downstream) {
- Supplier<D> downstreamSupplier = downstream.resultSupplier();
- BiFunction<D, ? super T, D> downstreamAccumulator = downstream.accumulator();
- BiFunction<M, T, M> accumulator = (m, t) -> {
+ public static <T, K, D, A, M extends Map<K, D>>
+ Collector<T, ?, M> groupingBy(Function<? super T, ? extends K> classifier,
+ Supplier<M> mapFactory,
+ Collector<? super T, A, D> downstream) {
+ Supplier<A> downstreamSupplier = downstream.supplier();
+ BiConsumer<A, ? super T> downstreamAccumulator = downstream.accumulator();
+ BiConsumer<Map<K, A>, T> accumulator = (m, t) -> {
K key = Objects.requireNonNull(classifier.apply(t), "element cannot be mapped to a null key");
- D oldContainer = m.computeIfAbsent(key, k -> downstreamSupplier.get());
- D newContainer = downstreamAccumulator.apply(oldContainer, t);
- if (newContainer != oldContainer)
- m.put(key, newContainer);
- return m;
+ A container = m.computeIfAbsent(key, k -> downstreamSupplier.get());
+ downstreamAccumulator.accept(container, t);
};
- return new CollectorImpl<>(mapFactory, accumulator, mapMerger(downstream.combiner()), CH_STRICT);
+ BinaryOperator<Map<K, A>> merger = Collectors.<K, A, Map<K, A>>mapMerger(downstream.combiner());
+ @SuppressWarnings("unchecked")
+ Supplier<Map<K, A>> mangledFactory = (Supplier<Map<K, A>>) mapFactory;
+
+ if (downstream.characteristics().contains(Collector.Characteristics.IDENTITY_FINISH)) {
+ return new CollectorImpl<>(mangledFactory, accumulator, merger, CH_ID);
+ }
+ else {
+ @SuppressWarnings("unchecked")
+ Function<A, A> downstreamFinisher = (Function<A, A>) downstream.finisher();
+ Function<Map<K, A>, M> finisher = intermediate -> {
+ intermediate.replaceAll((k, v) -> downstreamFinisher.apply(v));
+ @SuppressWarnings("unchecked")
+ M castResult = (M) intermediate;
+ return castResult;
+ };
+ return new CollectorImpl<>(mangledFactory, accumulator, merger, finisher, CH_NOID);
+ }
}
/**
- * Returns a {@code Collector} implementing a concurrent "group by"
+ * Returns a concurrent {@code Collector} implementing a "group by"
* operation on input elements of type {@code T}, grouping elements
* according to a classification function.
*
@@ -716,12 +837,13 @@
* @see #groupingByConcurrent(Function, Supplier, Collector)
*/
public static <T, K>
- Collector<T, ConcurrentMap<K, List<T>>> groupingByConcurrent(Function<? super T, ? extends K> classifier) {
+ Collector<T, ?, ConcurrentMap<K, List<T>>>
+ groupingByConcurrent(Function<? super T, ? extends K> classifier) {
return groupingByConcurrent(classifier, ConcurrentHashMap::new, toList());
}
/**
- * Returns a {@code Collector} implementing a concurrent cascaded "group by"
+ * Returns a concurrent {@code Collector} implementing a cascaded "group by"
* operation on input elements of type {@code T}, grouping elements
* according to a classification function, and then performing a reduction
* operation on the values associated with a given key using the specified
@@ -739,12 +861,13 @@
* where the city names are sorted:
* <pre>{@code
* ConcurrentMap<City, Set<String>> namesByCity
- * = people.stream().collect(groupingByConcurrent(Person::getCity, TreeMap::new,
+ * = people.stream().collect(groupingByConcurrent(Person::getCity, ConcurrentSkipListMap::new,
* mapping(Person::getLastName, toSet())));
* }</pre>
*
* @param <T> the type of the input elements
* @param <K> the type of the keys
+ * @param <A> the intermediate accumulation type of the downstream collector
* @param <D> the result type of the downstream reduction
* @param classifier a classifier function mapping input elements to keys
* @param downstream a {@code Collector} implementing the downstream reduction
@@ -754,9 +877,9 @@
* @see #groupingByConcurrent(Function)
* @see #groupingByConcurrent(Function, Supplier, Collector)
*/
- public static <T, K, D>
- Collector<T, ConcurrentMap<K, D>> groupingByConcurrent(Function<? super T, ? extends K> classifier,
- Collector<? super T, D> downstream) {
+ public static <T, K, A, D>
+ Collector<T, ?, ConcurrentMap<K, D>> groupingByConcurrent(Function<? super T, ? extends K> classifier,
+ Collector<? super T, A, D> downstream) {
return groupingByConcurrent(classifier, ConcurrentHashMap::new, downstream);
}
@@ -787,6 +910,7 @@
*
* @param <T> the type of the input elements
* @param <K> the type of the keys
+ * @param <A> the intermediate accumulation type of the downstream collector
* @param <D> the result type of the downstream reduction
* @param <M> the type of the resulting {@code ConcurrentMap}
* @param classifier a classifier function mapping input elements to keys
@@ -799,51 +923,46 @@
* @see #groupingByConcurrent(Function, Collector)
* @see #groupingBy(Function, Supplier, Collector)
*/
- public static <T, K, D, M extends ConcurrentMap<K, D>>
- Collector<T, M> groupingByConcurrent(Function<? super T, ? extends K> classifier,
- Supplier<M> mapFactory,
- Collector<? super T, D> downstream) {
- Supplier<D> downstreamSupplier = downstream.resultSupplier();
- BiFunction<D, ? super T, D> downstreamAccumulator = downstream.accumulator();
- BinaryOperator<M> combiner = mapMerger(downstream.combiner());
+ public static <T, K, A, D, M extends ConcurrentMap<K, D>>
+ Collector<T, ?, M> groupingByConcurrent(Function<? super T, ? extends K> classifier,
+ Supplier<M> mapFactory,
+ Collector<? super T, A, D> downstream) {
+ Supplier<A> downstreamSupplier = downstream.supplier();
+ BiConsumer<A, ? super T> downstreamAccumulator = downstream.accumulator();
+ BinaryOperator<ConcurrentMap<K, A>> merger = Collectors.<K, A, ConcurrentMap<K, A>>mapMerger(downstream.combiner());
+ @SuppressWarnings("unchecked")
+ Supplier<ConcurrentMap<K, A>> mangledFactory = (Supplier<ConcurrentMap<K, A>>) mapFactory;
+ BiConsumer<ConcurrentMap<K, A>, T> accumulator;
if (downstream.characteristics().contains(Collector.Characteristics.CONCURRENT)) {
- BiFunction<M, T, M> accumulator = (m, t) -> {
+ accumulator = (m, t) -> {
K key = Objects.requireNonNull(classifier.apply(t), "element cannot be mapped to a null key");
- downstreamAccumulator.apply(m.computeIfAbsent(key, k -> downstreamSupplier.get()), t);
- return m;
- };
- return new CollectorImpl<>(mapFactory, accumulator, combiner, CH_CONCURRENT);
- } else if (downstream.characteristics().contains(Collector.Characteristics.STRICTLY_MUTATIVE)) {
- BiFunction<M, T, M> accumulator = (m, t) -> {
- K key = Objects.requireNonNull(classifier.apply(t), "element cannot be mapped to a null key");
- D resultContainer = m.computeIfAbsent(key, k -> downstreamSupplier.get());
- synchronized (resultContainer) {
- downstreamAccumulator.apply(resultContainer, t);
- }
- return m;
+ A resultContainer = m.computeIfAbsent(key, k -> downstreamSupplier.get());
+ downstreamAccumulator.accept(resultContainer, t);
};
- return new CollectorImpl<>(mapFactory, accumulator, combiner, CH_CONCURRENT);
- } else {
- BiFunction<M, T, M> accumulator = (m, t) -> {
+ }
+ else {
+ accumulator = (m, t) -> {
K key = Objects.requireNonNull(classifier.apply(t), "element cannot be mapped to a null key");
- do {
- D oldResult = m.computeIfAbsent(key, k -> downstreamSupplier.get());
- if (oldResult == null) {
- if (m.putIfAbsent(key, downstreamAccumulator.apply(null, t)) == null)
- return m;
- } else {
- synchronized (oldResult) {
- if (m.get(key) != oldResult)
- continue;
- D newResult = downstreamAccumulator.apply(oldResult, t);
- if (oldResult != newResult)
- m.put(key, newResult);
- return m;
- }
- }
- } while (true);
+ A resultContainer = m.computeIfAbsent(key, k -> downstreamSupplier.get());
+ synchronized (resultContainer) {
+ downstreamAccumulator.accept(resultContainer, t);
+ }
};
- return new CollectorImpl<>(mapFactory, accumulator, combiner, CH_CONCURRENT);
+ }
+
+ if (downstream.characteristics().contains(Collector.Characteristics.IDENTITY_FINISH)) {
+ return new CollectorImpl<>(mangledFactory, accumulator, merger, CH_CONCURRENT_ID);
+ }
+ else {
+ @SuppressWarnings("unchecked")
+ Function<A, A> downstreamFinisher = (Function<A, A>) downstream.finisher();
+ Function<ConcurrentMap<K, A>, M> finisher = intermediate -> {
+ intermediate.replaceAll((k, v) -> downstreamFinisher.apply(v));
+ @SuppressWarnings("unchecked")
+ M castResult = (M) intermediate;
+ return castResult;
+ };
+ return new CollectorImpl<>(mangledFactory, accumulator, merger, finisher, CH_CONCURRENT_NOID);
}
}
@@ -862,7 +981,7 @@
* @see #partitioningBy(Predicate, Collector)
*/
public static <T>
- Collector<T, Map<Boolean, List<T>>> partitioningBy(Predicate<? super T> predicate) {
+ Collector<T, ?, Map<Boolean, List<T>>> partitioningBy(Predicate<? super T> predicate) {
return partitioningBy(predicate, toList());
}
@@ -877,6 +996,7 @@
* serializability, or thread-safety of the {@code Map} returned.
*
* @param <T> the type of the input elements
+ * @param <A> the intermediate accumulation type of the downstream collector
* @param <D> the result type of the downstream reduction
* @param predicate a predicate used for classifying input elements
* @param downstream a {@code Collector} implementing the downstream
@@ -886,52 +1006,43 @@
*
* @see #partitioningBy(Predicate)
*/
- public static <T, D>
- Collector<T, Map<Boolean, D>> partitioningBy(Predicate<? super T> predicate,
- Collector<? super T, D> downstream) {
- BiFunction<D, ? super T, D> downstreamAccumulator = downstream.accumulator();
- BiFunction<Map<Boolean, D>, T, Map<Boolean, D>> accumulator = (result, t) -> {
+ public static <T, D, A>
+ Collector<T, ?, Map<Boolean, D>> partitioningBy(Predicate<? super T> predicate,
+ Collector<? super T, A, D> downstream) {
+ @SuppressWarnings("unchecked")
+ BiConsumer<D, ? super T> downstreamAccumulator = (BiConsumer<D, ? super T>) downstream.accumulator();
+ BiConsumer<Map<Boolean, A>, T> accumulator = (result, t) -> {
Partition<D> asPartition = ((Partition<D>) result);
- if (predicate.test(t)) {
- D newResult = downstreamAccumulator.apply(asPartition.forTrue, t);
- if (newResult != asPartition.forTrue)
- asPartition.forTrue = newResult;
- } else {
- D newResult = downstreamAccumulator.apply(asPartition.forFalse, t);
- if (newResult != asPartition.forFalse)
- asPartition.forFalse = newResult;
- }
- return result;
+ downstreamAccumulator.accept(predicate.test(t) ? asPartition.forTrue : asPartition.forFalse, t);
+ };
+ BinaryOperator<A> op = downstream.combiner();
+ BinaryOperator<Map<Boolean, A>> merger = (m1, m2) -> {
+ Partition<A> left = (Partition<A>) m1;
+ Partition<A> right = (Partition<A>) m2;
+ return new Partition<>(op.apply(left.forTrue, right.forTrue),
+ op.apply(left.forFalse, right.forFalse));
};
- return new CollectorImpl<>(() -> new Partition<>(downstream.resultSupplier().get(),
- downstream.resultSupplier().get()),
- accumulator, partitionMerger(downstream.combiner()), CH_STRICT);
+ Supplier<Map<Boolean, A>> supplier = () -> new Partition<>(downstream.supplier().get(),
+ downstream.supplier().get());
+ if (downstream.characteristics().contains(Collector.Characteristics.IDENTITY_FINISH)) {
+ return new CollectorImpl<>(supplier, accumulator, merger, CH_ID);
+ }
+ else {
+ Function<Map<Boolean, A>, Map<Boolean, D>> finisher = (Map<Boolean, A> par) -> {
+ Partition<A> asAPartition = (Partition<A>) par;
+ return new Partition<>(downstream.finisher().apply(asAPartition.forTrue),
+ downstream.finisher().apply(asAPartition.forFalse));
+ };
+ return new CollectorImpl<>(supplier, accumulator, merger, finisher, CH_NOID);
+ }
}
/**
- * Merge function for two partitions, given a merge function for the
- * elements.
- */
- private static <D> BinaryOperator<Map<Boolean, D>> partitionMerger(BinaryOperator<D> op) {
- return (m1, m2) -> {
- Partition<D> left = (Partition<D>) m1;
- Partition<D> right = (Partition<D>) m2;
- if (left.forFalse == null)
- left.forFalse = right.forFalse;
- else if (right.forFalse != null)
- left.forFalse = op.apply(left.forFalse, right.forFalse);
- if (left.forTrue == null)
- left.forTrue = right.forTrue;
- else if (right.forTrue != null)
- left.forTrue = op.apply(left.forTrue, right.forTrue);
- return left;
- };
- }
-
- /**
- * Accumulate elements into a {@code Map} whose keys and values are the
- * result of applying mapping functions to the input elements.
- * If the mapped keys contains duplicates (according to
+ * Returns a {@code Collector} that accumulate elements into a
+ * {@code Map} whose keys and values are the result of applying the provided
+ * mapping functions to the input elements.
+ *
+ * <p>If the mapped keys contains duplicates (according to
* {@link Object#equals(Object)}), an {@code IllegalStateException} is
* thrown when the collection operation is performed. If the mapped keys
* may have duplicates, use {@link #toMap(Function, Function, BinaryOperator)}
@@ -970,24 +1081,26 @@
* @see #toConcurrentMap(Function, Function)
*/
public static <T, K, U>
- Collector<T, Map<K,U>> toMap(Function<? super T, ? extends K> keyMapper,
- Function<? super T, ? extends U> valueMapper) {
+ Collector<T, ?, Map<K,U>> toMap(Function<? super T, ? extends K> keyMapper,
+ Function<? super T, ? extends U> valueMapper) {
return toMap(keyMapper, valueMapper, throwingMerger(), HashMap::new);
}
/**
- * Accumulate elements into a {@code Map} whose keys and values are the
- * result of applying mapping functions to the input elements. If the mapped
+ * Returns a {@code Collector} that accumulate elements into a
+ * {@code Map} whose keys and values are the result of applying the provided
+ * mapping functions to the input elements.
+ *
+ * <p>If the mapped
* keys contains duplicates (according to {@link Object#equals(Object)}),
* the value mapping function is applied to each equal element, and the
* results are merged using the provided merging function.
*
* @apiNote
* There are multiple ways to deal with collisions between multiple elements
- * mapping to the same key. There are some predefined merging functions,
- * such as {@link #throwingMerger()}, {@link #firstWinsMerger()}, and
- * {@link #lastWinsMerger()}, that implement common policies, or you can
- * implement custom policies easily. For example, if you have a stream
+ * mapping to the same key. The other forms of {@code toMap} simply use
+ * a merge function that throws unconditionally, but you can easily write
+ * more flexible merge policies. For example, if you have a stream
* of {@code Person}, and you want to produce a "phone book" mapping name to
* address, but it is possible that two persons have the same name, you can
* do as follows to gracefully deals with these collisions, and produce a
@@ -1018,15 +1131,18 @@
* @see #toConcurrentMap(Function, Function, BinaryOperator)
*/
public static <T, K, U>
- Collector<T, Map<K,U>> toMap(Function<? super T, ? extends K> keyMapper,
- Function<? super T, ? extends U> valueMapper,
- BinaryOperator<U> mergeFunction) {
+ Collector<T, ?, Map<K,U>> toMap(Function<? super T, ? extends K> keyMapper,
+ Function<? super T, ? extends U> valueMapper,
+ BinaryOperator<U> mergeFunction) {
return toMap(keyMapper, valueMapper, mergeFunction, HashMap::new);
}
/**
- * Accumulate elements into a {@code Map} whose keys and values are the
- * result of applying mapping functions to the input elements. If the mapped
+ * Returns a {@code Collector} that accumulate elements into a
+ * {@code Map} whose keys and values are the result of applying the provided
+ * mapping functions to the input elements.
+ *
+ * <p>If the mapped
* keys contains duplicates (according to {@link Object#equals(Object)}),
* the value mapping function is applied to each equal element, and the
* results are merged using the provided merging function. The {@code Map}
@@ -1054,22 +1170,22 @@
* @see #toConcurrentMap(Function, Function, BinaryOperator, Supplier)
*/
public static <T, K, U, M extends Map<K, U>>
- Collector<T, M> toMap(Function<? super T, ? extends K> keyMapper,
- Function<? super T, ? extends U> valueMapper,
- BinaryOperator<U> mergeFunction,
- Supplier<M> mapSupplier) {
- BiFunction<M, T, M> accumulator
- = (map, element) -> {
- map.merge(keyMapper.apply(element), valueMapper.apply(element), mergeFunction);
- return map;
- };
- return new CollectorImpl<>(mapSupplier, accumulator, mapMerger(mergeFunction), CH_STRICT);
+ Collector<T, ?, M> toMap(Function<? super T, ? extends K> keyMapper,
+ Function<? super T, ? extends U> valueMapper,
+ BinaryOperator<U> mergeFunction,
+ Supplier<M> mapSupplier) {
+ BiConsumer<M, T> accumulator
+ = (map, element) -> map.merge(keyMapper.apply(element),
+ valueMapper.apply(element), mergeFunction);
+ return new CollectorImpl<>(mapSupplier, accumulator, mapMerger(mergeFunction), CH_ID);
}
/**
- * Accumulate elements into a {@code ConcurrentMap} whose keys and values
- * are the result of applying mapping functions to the input elements.
- * If the mapped keys contains duplicates (according to
+ * Returns a {@code Collector} that accumulate elements into a
+ * {@code ConcurrentMap} whose keys and values are the result of applying
+ * the provided mapping functions to the input elements.
+ *
+ * <p>If the mapped keys contains duplicates (according to
* {@link Object#equals(Object)}), an {@code IllegalStateException} is
* thrown when the collection operation is performed. If the mapped keys
* may have duplicates, use
@@ -1112,24 +1228,25 @@
* @see #toConcurrentMap(Function, Function, BinaryOperator, Supplier)
*/
public static <T, K, U>
- Collector<T, ConcurrentMap<K,U>> toConcurrentMap(Function<? super T, ? extends K> keyMapper,
- Function<? super T, ? extends U> valueMapper) {
+ Collector<T, ?, ConcurrentMap<K,U>> toConcurrentMap(Function<? super T, ? extends K> keyMapper,
+ Function<? super T, ? extends U> valueMapper) {
return toConcurrentMap(keyMapper, valueMapper, throwingMerger(), ConcurrentHashMap::new);
}
/**
- * Accumulate elements into a {@code ConcurrentMap} whose keys and values
- * are the result of applying mapping functions to the input elements. If
- * the mapped keys contains duplicates (according to {@link Object#equals(Object)}),
+ * Returns a {@code Collector} that accumulate elements into a
+ * {@code ConcurrentMap} whose keys and values are the result of applying
+ * the provided mapping functions to the input elements.
+ *
+ * <p>If the mapped keys contains duplicates (according to {@link Object#equals(Object)}),
* the value mapping function is applied to each equal element, and the
* results are merged using the provided merging function.
*
* @apiNote
* There are multiple ways to deal with collisions between multiple elements
- * mapping to the same key. There are some predefined merging functions,
- * such as {@link #throwingMerger()}, {@link #firstWinsMerger()}, and
- * {@link #lastWinsMerger()}, that implement common policies, or you can
- * implement custom policies easily. For example, if you have a stream
+ * mapping to the same key. The other forms of {@code toConcurrentMap} simply use
+ * a merge function that throws unconditionally, but you can easily write
+ * more flexible merge policies. For example, if you have a stream
* of {@code Person}, and you want to produce a "phone book" mapping name to
* address, but it is possible that two persons have the same name, you can
* do as follows to gracefully deals with these collisions, and produce a
@@ -1163,16 +1280,19 @@
* @see #toMap(Function, Function, BinaryOperator)
*/
public static <T, K, U>
- Collector<T, ConcurrentMap<K,U>> toConcurrentMap(Function<? super T, ? extends K> keyMapper,
- Function<? super T, ? extends U> valueMapper,
- BinaryOperator<U> mergeFunction) {
+ Collector<T, ?, ConcurrentMap<K,U>>
+ toConcurrentMap(Function<? super T, ? extends K> keyMapper,
+ Function<? super T, ? extends U> valueMapper,
+ BinaryOperator<U> mergeFunction) {
return toConcurrentMap(keyMapper, valueMapper, mergeFunction, ConcurrentHashMap::new);
}
/**
- * Accumulate elements into a {@code ConcurrentMap} whose keys and values
- * are the result of applying mapping functions to the input elements. If
- * the mapped keys contains duplicates (according to {@link Object#equals(Object)}),
+ * Returns a {@code Collector} that accumulate elements into a
+ * {@code ConcurrentMap} whose keys and values are the result of applying
+ * the provided mapping functions to the input elements.
+ *
+ * <p>If the mapped keys contains duplicates (according to {@link Object#equals(Object)}),
* the value mapping function is applied to each equal element, and the
* results are merged using the provided merging function. The
* {@code ConcurrentMap} is created by a provided supplier function.
@@ -1202,15 +1322,14 @@
* @see #toMap(Function, Function, BinaryOperator, Supplier)
*/
public static <T, K, U, M extends ConcurrentMap<K, U>>
- Collector<T, M> toConcurrentMap(Function<? super T, ? extends K> keyMapper,
- Function<? super T, ? extends U> valueMapper,
- BinaryOperator<U> mergeFunction,
- Supplier<M> mapSupplier) {
- BiFunction<M, T, M> accumulator = (map, element) -> {
- map.merge(keyMapper.apply(element), valueMapper.apply(element), mergeFunction);
- return map;
- };
- return new CollectorImpl<>(mapSupplier, accumulator, mapMerger(mergeFunction), CH_CONCURRENT);
+ Collector<T, ?, M> toConcurrentMap(Function<? super T, ? extends K> keyMapper,
+ Function<? super T, ? extends U> valueMapper,
+ BinaryOperator<U> mergeFunction,
+ Supplier<M> mapSupplier) {
+ BiConsumer<M, T> accumulator
+ = (map, element) -> map.merge(keyMapper.apply(element),
+ valueMapper.apply(element), mergeFunction);
+ return new CollectorImpl<>(mapSupplier, accumulator, mapMerger(mergeFunction), CH_CONCURRENT_ID);
}
/**
@@ -1222,14 +1341,15 @@
* @param mapper a mapping function to apply to each element
* @return a {@code Collector} implementing the summary-statistics reduction
*
- * @see #toDoubleSummaryStatistics(ToDoubleFunction)
- * @see #toLongSummaryStatistics(ToLongFunction)
+ * @see #summarizingDouble(ToDoubleFunction)
+ * @see #summarizingLong(ToLongFunction)
*/
public static <T>
- Collector<T, IntSummaryStatistics> toIntSummaryStatistics(ToIntFunction<? super T> mapper) {
- return new CollectorImpl<>(IntSummaryStatistics::new,
- (r, t) -> { r.accept(mapper.applyAsInt(t)); return r; },
- (l, r) -> { l.combine(r); return l; }, CH_STRICT);
+ Collector<T, ?, IntSummaryStatistics> summarizingInt(ToIntFunction<? super T> mapper) {
+ return new CollectorImpl<T, IntSummaryStatistics, IntSummaryStatistics>(
+ IntSummaryStatistics::new,
+ (r, t) -> r.accept(mapper.applyAsInt(t)),
+ (l, r) -> { l.combine(r); return l; }, CH_ID);
}
/**
@@ -1241,14 +1361,15 @@
* @param mapper the mapping function to apply to each element
* @return a {@code Collector} implementing the summary-statistics reduction
*
- * @see #toDoubleSummaryStatistics(ToDoubleFunction)
- * @see #toIntSummaryStatistics(ToIntFunction)
+ * @see #summarizingDouble(ToDoubleFunction)
+ * @see #summarizingInt(ToIntFunction)
*/
public static <T>
- Collector<T, LongSummaryStatistics> toLongSummaryStatistics(ToLongFunction<? super T> mapper) {
- return new CollectorImpl<>(LongSummaryStatistics::new,
- (r, t) -> { r.accept(mapper.applyAsLong(t)); return r; },
- (l, r) -> { l.combine(r); return l; }, CH_STRICT);
+ Collector<T, ?, LongSummaryStatistics> summarizingLong(ToLongFunction<? super T> mapper) {
+ return new CollectorImpl<T, LongSummaryStatistics, LongSummaryStatistics>(
+ LongSummaryStatistics::new,
+ (r, t) -> r.accept(mapper.applyAsLong(t)),
+ (l, r) -> { l.combine(r); return l; }, CH_ID);
}
/**
@@ -1260,14 +1381,15 @@
* @param mapper a mapping function to apply to each element
* @return a {@code Collector} implementing the summary-statistics reduction
*
- * @see #toLongSummaryStatistics(ToLongFunction)
- * @see #toIntSummaryStatistics(ToIntFunction)
+ * @see #summarizingLong(ToLongFunction)
+ * @see #summarizingInt(ToIntFunction)
*/
public static <T>
- Collector<T, DoubleSummaryStatistics> toDoubleSummaryStatistics(ToDoubleFunction<? super T> mapper) {
- return new CollectorImpl<>(DoubleSummaryStatistics::new,
- (r, t) -> { r.accept(mapper.applyAsDouble(t)); return r; },
- (l, r) -> { l.combine(r); return l; }, CH_STRICT);
+ Collector<T, ?, DoubleSummaryStatistics> summarizingDouble(ToDoubleFunction<? super T> mapper) {
+ return new CollectorImpl<T, DoubleSummaryStatistics, DoubleSummaryStatistics>(
+ DoubleSummaryStatistics::new,
+ (r, t) -> r.accept(mapper.applyAsDouble(t)),
+ (l, r) -> { l.combine(r); return l; }, CH_ID);
}
/**
@@ -1276,8 +1398,8 @@
private static final class Partition<T>
extends AbstractMap<Boolean, T>
implements Map<Boolean, T> {
- T forTrue;
- T forFalse;
+ final T forTrue;
+ final T forFalse;
Partition(T forTrue, T forFalse) {
this.forTrue = forTrue;
@@ -1289,24 +1411,9 @@
return new AbstractSet<Map.Entry<Boolean, T>>() {
@Override
public Iterator<Map.Entry<Boolean, T>> iterator() {
-
- return new Iterator<Map.Entry<Boolean, T>>() {
- int state = 0;
-
- @Override
- public boolean hasNext() {
- return state < 2;
- }
-
- @Override
- public Map.Entry<Boolean, T> next() {
- if (state >= 2)
- throw new NoSuchElementException();
- return (state++ == 0)
- ? new SimpleImmutableEntry<>(false, forFalse)
- : new SimpleImmutableEntry<>(true, forTrue);
- }
- };
+ Map.Entry<Boolean, T> falseEntry = new SimpleImmutableEntry<>(false, forFalse);
+ Map.Entry<Boolean, T> trueEntry = new SimpleImmutableEntry<>(true, forTrue);
+ return Arrays.asList(falseEntry, trueEntry).iterator();
}
@Override
--- a/jdk/test/java/util/stream/test/org/openjdk/tests/java/util/stream/TabulatorsTest.java Tue Aug 06 16:01:39 2013 -0700
+++ b/jdk/test/java/util/stream/test/org/openjdk/tests/java/util/stream/TabulatorsTest.java Fri Jun 28 16:26:54 2013 -0400
@@ -23,13 +23,17 @@
package org.openjdk.tests.java.util.stream;
import java.util.ArrayList;
+import java.util.Arrays;
import java.util.Collection;
+import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
+import java.util.Set;
+import java.util.StringJoiner;
import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentSkipListMap;
@@ -53,7 +57,10 @@
import static java.util.stream.Collectors.partitioningBy;
import static java.util.stream.Collectors.reducing;
import static java.util.stream.Collectors.toCollection;
+import static java.util.stream.Collectors.toConcurrentMap;
import static java.util.stream.Collectors.toList;
+import static java.util.stream.Collectors.toMap;
+import static java.util.stream.Collectors.toSet;
import static java.util.stream.LambdaTestHelpers.assertContents;
import static java.util.stream.LambdaTestHelpers.assertContentsUnordered;
import static java.util.stream.LambdaTestHelpers.mDoubler;
@@ -65,16 +72,6 @@
*/
@SuppressWarnings({"rawtypes", "unchecked"})
public class TabulatorsTest extends OpTestCase {
- // There are 8 versions of groupingBy:
- // groupingBy: { map supplier, not } x { downstream collector, not } x { concurrent, not }
- // There are 2 versions of partition: { map supplier, not }
- // There are 4 versions of toMap
- // mappedTo(function, mapSupplier?, mergeFunction?)
- // Each variety needs at least one test
- // Plus a variety of multi-level tests (groupBy(..., partition), partition(..., groupBy))
- // Plus negative tests for mapping to null
- // Each test should be matched by a nest of asserters (see TabulationAssertion...)
-
private static abstract class TabulationAssertion<T, U> {
abstract void assertValue(U value,
@@ -101,7 +98,7 @@
boolean ordered) throws ReflectiveOperationException {
if (!clazz.isAssignableFrom(map.getClass()))
fail(String.format("Class mismatch in GroupedMapAssertion: %s, %s", clazz, map.getClass()));
- assertContentsUnordered(map.keySet(), source.get().map(classifier).collect(Collectors.toSet()));
+ assertContentsUnordered(map.keySet(), source.get().map(classifier).collect(toSet()));
for (Map.Entry<K, ? extends V> entry : map.entrySet()) {
K key = entry.getKey();
downstream.assertValue(entry.getValue(),
@@ -111,6 +108,39 @@
}
}
+ static class ToMapAssertion<T, K, V, M extends Map<K,V>> extends TabulationAssertion<T, M> {
+ private final Class<? extends Map> clazz;
+ private final Function<T, K> keyFn;
+ private final Function<T, V> valueFn;
+ private final BinaryOperator<V> mergeFn;
+
+ ToMapAssertion(Function<T, K> keyFn,
+ Function<T, V> valueFn,
+ BinaryOperator<V> mergeFn,
+ Class<? extends Map> clazz) {
+ this.clazz = clazz;
+ this.keyFn = keyFn;
+ this.valueFn = valueFn;
+ this.mergeFn = mergeFn;
+ }
+
+ @Override
+ void assertValue(M map, Supplier<Stream<T>> source, boolean ordered) throws ReflectiveOperationException {
+ Set<K> uniqueKeys = source.get().map(keyFn).collect(toSet());
+ assertTrue(clazz.isAssignableFrom(map.getClass()));
+ assertEquals(uniqueKeys, map.keySet());
+ source.get().forEach(t -> {
+ K key = keyFn.apply(t);
+ V v = source.get()
+ .filter(e -> key.equals(keyFn.apply(e)))
+ .map(valueFn)
+ .reduce(mergeFn)
+ .get();
+ assertEquals(map.get(key), v);
+ });
+ }
+ }
+
static class PartitionAssertion<T, D> extends TabulationAssertion<T, Map<Boolean,D>> {
private final Predicate<T> predicate;
private final TabulationAssertion<T,D> downstream;
@@ -204,7 +234,7 @@
private <T> ResultAsserter<T> mapTabulationAsserter(boolean ordered) {
return (act, exp, ord, par) -> {
- if (par & (!ordered || !ord)) {
+ if (par && (!ordered || !ord)) {
TabulatorsTest.nestedMapEqualityAssertion(act, exp);
}
else {
@@ -215,7 +245,7 @@
private<T, M extends Map>
void exerciseMapTabulation(TestData<T, Stream<T>> data,
- Collector<T, ? extends M> collector,
+ Collector<T, ?, ? extends M> collector,
TabulationAssertion<T, M> assertion)
throws ReflectiveOperationException {
boolean ordered = !collector.characteristics().contains(Collector.Characteristics.UNORDERED);
@@ -248,6 +278,172 @@
assertEquals(o1, o2);
}
+ private<T, R> void assertCollect(TestData.OfRef<T> data,
+ Collector<T, ?, R> collector,
+ Function<Stream<T>, R> streamReduction) {
+ R check = streamReduction.apply(data.stream());
+ withData(data).terminal(s -> s.collect(collector)).expectedResult(check).exercise();
+ }
+
+ @Test(dataProvider = "StreamTestData<Integer>", dataProviderClass = StreamTestDataProvider.class)
+ public void testReduce(String name, TestData.OfRef<Integer> data) throws ReflectiveOperationException {
+ assertCollect(data, Collectors.reducing(0, Integer::sum),
+ s -> s.reduce(0, Integer::sum));
+ assertCollect(data, Collectors.reducing(Integer.MAX_VALUE, Integer::min),
+ s -> s.min(Integer::compare).orElse(Integer.MAX_VALUE));
+ assertCollect(data, Collectors.reducing(Integer.MIN_VALUE, Integer::max),
+ s -> s.max(Integer::compare).orElse(Integer.MIN_VALUE));
+
+ assertCollect(data, Collectors.reducing(Integer::sum),
+ s -> s.reduce(Integer::sum));
+ assertCollect(data, Collectors.minBy(Comparator.naturalOrder()),
+ s -> s.min(Integer::compare));
+ assertCollect(data, Collectors.maxBy(Comparator.naturalOrder()),
+ s -> s.max(Integer::compare));
+
+ assertCollect(data, Collectors.reducing(0, x -> x*2, Integer::sum),
+ s -> s.map(x -> x*2).reduce(0, Integer::sum));
+
+ assertCollect(data, Collectors.summingLong(x -> x * 2L),
+ s -> s.map(x -> x*2L).reduce(0L, Long::sum));
+ assertCollect(data, Collectors.summingInt(x -> x * 2),
+ s -> s.map(x -> x*2).reduce(0, Integer::sum));
+ assertCollect(data, Collectors.summingDouble(x -> x * 2.0d),
+ s -> s.map(x -> x * 2.0d).reduce(0.0d, Double::sum));
+
+ assertCollect(data, Collectors.averagingInt(x -> x * 2),
+ s -> s.mapToInt(x -> x * 2).average().orElse(0));
+ assertCollect(data, Collectors.averagingLong(x -> x * 2),
+ s -> s.mapToLong(x -> x * 2).average().orElse(0));
+ assertCollect(data, Collectors.averagingDouble(x -> x * 2),
+ s -> s.mapToDouble(x -> x * 2).average().orElse(0));
+
+ // Test explicit Collector.of
+ Collector<Integer, long[], Double> avg2xint = Collector.of(() -> new long[2],
+ (a, b) -> {
+ a[0] += b * 2;
+ a[1]++;
+ },
+ (a, b) -> {
+ a[0] += b[0];
+ a[1] += b[1];
+ return a;
+ },
+ a -> a[1] == 0 ? 0.0d : (double) a[0] / a[1]);
+ assertCollect(data, avg2xint,
+ s -> s.mapToInt(x -> x * 2).average().orElse(0));
+ }
+
+ @Test(dataProvider = "StreamTestData<Integer>", dataProviderClass = StreamTestDataProvider.class)
+ public void testJoin(String name, TestData.OfRef<Integer> data) throws ReflectiveOperationException {
+ withData(data)
+ .terminal(s -> s.map(Object::toString).collect(Collectors.joining()))
+ .expectedResult(join(data, ""))
+ .exercise();
+
+ Collector<String, StringBuilder, String> likeJoining = Collector.of(StringBuilder::new, StringBuilder::append, (sb1, sb2) -> sb1.append(sb2.toString()), StringBuilder::toString);
+ withData(data)
+ .terminal(s -> s.map(Object::toString).collect(likeJoining))
+ .expectedResult(join(data, ""))
+ .exercise();
+
+ withData(data)
+ .terminal(s -> s.map(Object::toString).collect(Collectors.joining(",")))
+ .expectedResult(join(data, ","))
+ .exercise();
+
+ withData(data)
+ .terminal(s -> s.map(Object::toString).collect(Collectors.joining(",", "[", "]")))
+ .expectedResult("[" + join(data, ",") + "]")
+ .exercise();
+
+ withData(data)
+ .terminal(s -> s.map(Object::toString)
+ .collect(StringBuilder::new, StringBuilder::append, StringBuilder::append)
+ .toString())
+ .expectedResult(join(data, ""))
+ .exercise();
+
+ withData(data)
+ .terminal(s -> s.map(Object::toString)
+ .collect(() -> new StringJoiner(","),
+ (sj, cs) -> sj.add(cs),
+ (j1, j2) -> j1.merge(j2))
+ .toString())
+ .expectedResult(join(data, ","))
+ .exercise();
+
+ withData(data)
+ .terminal(s -> s.map(Object::toString)
+ .collect(() -> new StringJoiner(",", "[", "]"),
+ (sj, cs) -> sj.add(cs),
+ (j1, j2) -> j1.merge(j2))
+ .toString())
+ .expectedResult("[" + join(data, ",") + "]")
+ .exercise();
+ }
+
+ private<T> String join(TestData.OfRef<T> data, String delim) {
+ StringBuilder sb = new StringBuilder();
+ boolean first = true;
+ for (T i : data) {
+ if (!first)
+ sb.append(delim);
+ sb.append(i.toString());
+ first = false;
+ }
+ return sb.toString();
+ }
+
+ @Test(dataProvider = "StreamTestData<Integer>", dataProviderClass = StreamTestDataProvider.class)
+ public void testSimpleToMap(String name, TestData.OfRef<Integer> data) throws ReflectiveOperationException {
+ Function<Integer, Integer> keyFn = i -> i * 2;
+ Function<Integer, Integer> valueFn = i -> i * 4;
+
+ List<Integer> dataAsList = Arrays.asList(data.stream().toArray(Integer[]::new));
+ Set<Integer> dataAsSet = new HashSet<>(dataAsList);
+
+ BinaryOperator<Integer> sum = Integer::sum;
+ for (BinaryOperator<Integer> op : Arrays.asList((u, v) -> u,
+ (u, v) -> v,
+ sum)) {
+ try {
+ exerciseMapTabulation(data, toMap(keyFn, valueFn),
+ new ToMapAssertion<>(keyFn, valueFn, op, HashMap.class));
+ if (dataAsList.size() != dataAsSet.size())
+ fail("Expected ISE on input with duplicates");
+ }
+ catch (IllegalStateException e) {
+ if (dataAsList.size() == dataAsSet.size())
+ fail("Expected no ISE on input without duplicates");
+ }
+
+ exerciseMapTabulation(data, toMap(keyFn, valueFn, op),
+ new ToMapAssertion<>(keyFn, valueFn, op, HashMap.class));
+
+ exerciseMapTabulation(data, toMap(keyFn, valueFn, op, TreeMap::new),
+ new ToMapAssertion<>(keyFn, valueFn, op, TreeMap.class));
+ }
+
+ // For concurrent maps, only use commutative merge functions
+ try {
+ exerciseMapTabulation(data, toConcurrentMap(keyFn, valueFn),
+ new ToMapAssertion<>(keyFn, valueFn, sum, ConcurrentHashMap.class));
+ if (dataAsList.size() != dataAsSet.size())
+ fail("Expected ISE on input with duplicates");
+ }
+ catch (IllegalStateException e) {
+ if (dataAsList.size() == dataAsSet.size())
+ fail("Expected no ISE on input without duplicates");
+ }
+
+ exerciseMapTabulation(data, toConcurrentMap(keyFn, valueFn, sum),
+ new ToMapAssertion<>(keyFn, valueFn, sum, ConcurrentHashMap.class));
+
+ exerciseMapTabulation(data, toConcurrentMap(keyFn, valueFn, sum, ConcurrentSkipListMap::new),
+ new ToMapAssertion<>(keyFn, valueFn, sum, ConcurrentSkipListMap.class));
+ }
+
@Test(dataProvider = "StreamTestData<Integer>", dataProviderClass = StreamTestDataProvider.class)
public void testSimpleGroupBy(String name, TestData.OfRef<Integer> data) throws ReflectiveOperationException {
Function<Integer, Integer> classifier = i -> i % 3;