8015318: Extend Collector with 'finish' operation
Reviewed-by: mduigou
Contributed-by: brian.goetz@oracle.com
diff --git a/src/share/classes/java/util/DoubleSummaryStatistics.java b/src/share/classes/java/util/DoubleSummaryStatistics.java
index fb79c56..63c887e 100644
--- a/src/share/classes/java/util/DoubleSummaryStatistics.java
+++ b/src/share/classes/java/util/DoubleSummaryStatistics.java
@@ -25,6 +25,7 @@
package java.util;
import java.util.function.DoubleConsumer;
+import java.util.stream.Collector;
/**
* A state object for collecting statistics such as count, min, max, sum, and
@@ -35,24 +36,24 @@
* summary statistics on a stream of doubles with:
* <pre> {@code
* DoubleSummaryStatistics stats = doubleStream.collect(DoubleSummaryStatistics::new,
- * DoubleSummaryStatistics::accept,
- * DoubleSummaryStatistics::combine);
+ * DoubleSummaryStatistics::accept,
+ * DoubleSummaryStatistics::combine);
* }</pre>
*
* <p>{@code DoubleSummaryStatistics} can be used as a
- * {@linkplain java.util.stream.Stream#reduce(java.util.function.BinaryOperator) reduction}
+ * {@linkplain java.util.stream.Stream#collect(Collector) reduction}
* target for a {@linkplain java.util.stream.Stream stream}. For example:
*
* <pre> {@code
* DoubleSummaryStatistics stats = people.stream()
- * .collect(Collectors.toDoubleSummaryStatistics(Person::getWeight));
+ * .collect(Collectors.summarizingDouble(Person::getWeight));
*}</pre>
*
* This computes, in a single pass, the count of people, as well as the minimum,
* maximum, sum, and average of their weights.
*
* @implNote This implementation is not thread safe. However, it is safe to use
- * {@link java.util.stream.Collectors#toDoubleSummaryStatistics(java.util.function.ToDoubleFunction)
+ * {@link java.util.stream.Collectors#summarizingDouble(java.util.function.ToDoubleFunction)
* Collectors.toDoubleStatistics()} on a parallel stream, because the parallel
* implementation of {@link java.util.stream.Stream#collect Stream.collect()}
* provides the necessary partitioning, isolation, and merging of results for
@@ -152,7 +153,7 @@
}
/**
- * Returns the average of values recorded, or zero if no values have been
+ * Returns the arithmetic mean of values recorded, or zero if no values have been
* recorded. The average returned can vary depending upon the order in
* which values are recorded. This is due to accumulated rounding error in
* addition of values of differing magnitudes. Values sorted by increasing
@@ -160,7 +161,7 @@
* value is a {@code NaN} or the sum is at any point a {@code NaN} then the
* average will be {@code NaN}.
*
- * @return the average of values, or zero if none
+ * @return the arithmetic mean of values, or zero if none
*/
public final double getAverage() {
return getCount() > 0 ? getSum() / getCount() : 0.0d;
diff --git a/src/share/classes/java/util/IntSummaryStatistics.java b/src/share/classes/java/util/IntSummaryStatistics.java
index fcca329..f93436e 100644
--- a/src/share/classes/java/util/IntSummaryStatistics.java
+++ b/src/share/classes/java/util/IntSummaryStatistics.java
@@ -25,6 +25,7 @@
package java.util;
import java.util.function.IntConsumer;
+import java.util.stream.Collector;
/**
* A state object for collecting statistics such as count, min, max, sum, and
@@ -35,24 +36,24 @@
* summary statistics on a stream of ints with:
* <pre> {@code
* IntSummaryStatistics stats = intStream.collect(IntSummaryStatistics::new,
- * IntSummaryStatistics::accept,
- * IntSummaryStatistics::combine);
+ * IntSummaryStatistics::accept,
+ * IntSummaryStatistics::combine);
* }</pre>
*
* <p>{@code IntSummaryStatistics} can be used as a
- * {@linkplain java.util.stream.Stream#reduce(java.util.function.BinaryOperator) reduction}
+ * {@linkplain java.util.stream.Stream#collect(Collector) reduction}
* target for a {@linkplain java.util.stream.Stream stream}. For example:
*
* <pre> {@code
* IntSummaryStatistics stats = people.stream()
- * .collect(Collectors.toIntSummaryStatistics(Person::getDependents));
+ * .collect(Collectors.summarizingInt(Person::getDependents));
*}</pre>
*
* This computes, in a single pass, the count of people, as well as the minimum,
* maximum, sum, and average of their number of dependents.
*
* @implNote This implementation is not thread safe. However, it is safe to use
- * {@link java.util.stream.Collectors#toIntSummaryStatistics(java.util.function.ToIntFunction)
+ * {@link java.util.stream.Collectors#summarizingInt(java.util.function.ToIntFunction)
* Collectors.toIntStatistics()} on a parallel stream, because the parallel
* implementation of {@link java.util.stream.Stream#collect Stream.collect()}
* provides the necessary partitioning, isolation, and merging of results for
@@ -140,10 +141,10 @@
}
/**
- * Returns the average of values recorded, or zero if no values have been
+ * Returns the arithmetic mean of values recorded, or zero if no values have been
* recorded.
*
- * @return the average of values, or zero if none
+ * @return the arithmetic mean of values, or zero if none
*/
public final double getAverage() {
return getCount() > 0 ? (double) getSum() / getCount() : 0.0d;
diff --git a/src/share/classes/java/util/LongSummaryStatistics.java b/src/share/classes/java/util/LongSummaryStatistics.java
index 0e2da71..085aa29 100644
--- a/src/share/classes/java/util/LongSummaryStatistics.java
+++ b/src/share/classes/java/util/LongSummaryStatistics.java
@@ -26,6 +26,7 @@
import java.util.function.IntConsumer;
import java.util.function.LongConsumer;
+import java.util.stream.Collector;
/**
* A state object for collecting statistics such as count, min, max, sum, and
@@ -36,24 +37,24 @@
* summary statistics on a stream of longs with:
* <pre> {@code
* LongSummaryStatistics stats = longStream.collect(LongSummaryStatistics::new,
- * LongSummaryStatistics::accept,
- * LongSummaryStatistics::combine);
+ * LongSummaryStatistics::accept,
+ * LongSummaryStatistics::combine);
* }</pre>
*
* <p>{@code LongSummaryStatistics} can be used as a
- * {@linkplain java.util.stream.Stream#reduce(java.util.function.BinaryOperator) reduction}
+ * {@linkplain java.util.stream.Stream#collect(Collector)} reduction}
* target for a {@linkplain java.util.stream.Stream stream}. For example:
*
* <pre> {@code
* LongSummaryStatistics stats = people.stream()
- * .collect(Collectors.toLongSummaryStatistics(Person::getAge));
+ * .collect(Collectors.summarizingLong(Person::getAge));
*}</pre>
*
* This computes, in a single pass, the count of people, as well as the minimum,
- * maximum, sum, and average of their ages in milliseconds.
+ * maximum, sum, and average of their ages.
*
* @implNote This implementation is not thread safe. However, it is safe to use
- * {@link java.util.stream.Collectors#toLongSummaryStatistics(java.util.function.ToLongFunction)
+ * {@link java.util.stream.Collectors#summarizingLong(java.util.function.ToLongFunction)
* Collectors.toLongStatistics()} on a parallel stream, because the parallel
* implementation of {@link java.util.stream.Stream#collect Stream.collect()}
* provides the necessary partitioning, isolation, and merging of results for
@@ -152,10 +153,10 @@
}
/**
- * Returns the average of values recorded, or zero if no values have been
+ * Returns the arithmetic mean of values recorded, or zero if no values have been
* recorded.
*
- * @return The average of values, or zero if none
+ * @return The arithmetic mean of values, or zero if none
*/
public final double getAverage() {
return getCount() > 0 ? (double) getSum() / getCount() : 0.0d;
diff --git a/src/share/classes/java/util/StringJoiner.java b/src/share/classes/java/util/StringJoiner.java
index 66d49b6..d4050a4 100644
--- a/src/share/classes/java/util/StringJoiner.java
+++ b/src/share/classes/java/util/StringJoiner.java
@@ -49,16 +49,17 @@
* <p>
* A {@code StringJoiner} may be employed to create formatted output from a
* {@link java.util.stream.Stream} using
- * {@link java.util.stream.Collectors#toStringJoiner}. For example:
+ * {@link java.util.stream.Collectors#joining(CharSequence)}. For example:
*
* <pre> {@code
* List<Integer> numbers = Arrays.asList(1, 2, 3, 4);
* String commaSeparatedNumbers = numbers.stream()
* .map(i -> i.toString())
- * .collect(Collectors.toStringJoiner(", ")).toString();
+ * .collect(Collectors.joining(", "));
* }</pre>
*
- * @see java.util.stream.Collectors#toStringJoiner
+ * @see java.util.stream.Collectors#joining(CharSequence)
+ * @see java.util.stream.Collectors#joining(CharSequence, CharSequence, CharSequence)
* @since 1.8
*/
public final class StringJoiner {
diff --git a/src/share/classes/java/util/stream/Collector.java b/src/share/classes/java/util/stream/Collector.java
index 71bb227..4962917 100644
--- a/src/share/classes/java/util/stream/Collector.java
+++ b/src/share/classes/java/util/stream/Collector.java
@@ -25,40 +25,45 @@
package java.util.stream;
import java.util.Collections;
+import java.util.EnumSet;
import java.util.Set;
-import java.util.function.BiFunction;
+import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
+import java.util.function.Function;
import java.util.function.Supplier;
/**
* A <a href="package-summary.html#Reduction">reduction operation</a> that
- * supports folding input elements into a cumulative result. The result may be
- * a value or may be a mutable result container. Examples of operations
- * accumulating results into a mutable result container include: accumulating
- * input elements into a {@code Collection}; concatenating strings into a
- * {@code StringBuilder}; computing summary information about elements such as
- * sum, min, max, or average; computing "pivot table" summaries such as "maximum
- * valued transaction by seller", etc. Reduction operations can be performed
- * either sequentially or in parallel.
+ * folds input elements into a mutable result container, optionally transforming
+ * the accumulated result into a final representation after all input elements
+ * have been processed.
+ *
+ * <p>Examples of mutable reduction operations include:
+ * accumulating elements into a {@code Collection}; concatenating
+ * strings using a {@code StringBuilder}; computing summary information about
+ * elements such as sum, min, max, or average; computing "pivot table" summaries
+ * such as "maximum valued transaction by seller", etc. Reduction operations
+ * can be performed either sequentially or in parallel.
*
* <p>The following are examples of using the predefined {@code Collector}
* implementations in {@link Collectors} with the {@code Stream} API to perform
* mutable reduction tasks:
* <pre>{@code
- * // Accumulate elements into a List
- * List<String> list = stream.collect(Collectors.toList());
+ * // Accumulate names into a List
+ * List<String> list = people.stream().map(Person::getName).collect(Collectors.toList());
*
- * // Accumulate elements into a TreeSet
- * Set<String> list = stream.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(Comparators.comparing(Employee::getSalary)));
+ * .collect(Collectors.maxBy(Comparators.comparing(Employee::getSalary)))
+ * .get();
*
* // Group employees by department
* Map<Department, List<Employee>> byDept
@@ -66,7 +71,7 @@
* .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(Comparators.comparing(Employee::getSalary))));
@@ -74,43 +79,42 @@
* // 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>
*
- * <p>A {@code Collector} is specified by three functions that work together to
- * manage a result or result container. They are: creation of an initial
- * result, incorporating a new data element into a result, and combining two
- * results into one. The last function -- combining two results into one -- is
- * used during parallel operations, where subsets of the input are accumulated
- * in parallel, and then the subresults merged into a combined result. The
- * result may be a mutable container or a value. If the result is mutable, the
- * accumulation and combination functions may either mutate their left argument
- * and return that (such as adding elements to a collection), or return a new
- * result, in which case it should not perform any mutation.
+ * <p>A {@code Collector} is specified by four functions that work together to
+ * accumulate entries into a mutable result container, and optionally perform
+ * a final transform on the result. They are: creation of a new result container,
+ * incorporating a new data element into a result container, combining two
+ * result containers into one, and performing a final transform on the container.
+ * The combiner function is used during parallel operations, where
+ * subsets of the input are accumulated into separate result
+ * containers, and then the subresults merged into a combined result. The
+ * combiner function may merge one set of subresults into the other and return
+ * that, or it may return a new object to describe the combined results.
*
- * <p>Collectors also have a set of characteristics, including
- * {@link Characteristics#CONCURRENT} and
- * {@link Characteristics#STRICTLY_MUTATIVE}. These characteristics provide
+ * <p>Collectors also have a set of characteristics, such as
+ * {@link Characteristics#CONCURRENT}. These characteristics provide
* hints that can be used by a reduction implementation to provide better
* performance.
*
* <p>Libraries that implement reduction based on {@code Collector}, such as
* {@link Stream#collect(Collector)}, must adhere to the following constraints:
* <ul>
- * <li>The first argument passed to the accumulator function, and both
- * arguments passed to the combiner function, must be the result of a
- * previous invocation of {@link #resultSupplier()}, {@link #accumulator()},
- * or {@link #combiner()}.</li>
+ * <li>The first argument passed to the accumulator function, both
+ * arguments passed to the combiner function, and the argument passed to the
+ * finisher function must be the result of a previous invocation of the
+ * result supplier, accumulator, or combiner functions.</li>
* <li>The implementation should not do anything with the result of any of
* the result supplier, accumulator, or combiner functions other than to
- * pass them again to the accumulator or combiner functions, or return them
- * to the caller of the reduction operation.</li>
- * <li>If a result is passed to the accumulator or combiner function, and
- * the same object is not returned from that function, it is never used
- * again.</li>
- * <li>Once a result is passed to the combiner function, it is never passed
- * to the accumulator function again.</li>
+ * pass them again to the accumulator, combiner, or finisher functions,
+ * or return them to the caller of the reduction operation.</li>
+ * <li>If a result is passed to the combiner or finisher
+ * function, and the same object is not returned from that function, it is
+ * never used again.</li>
+ * <li>Once a result is passed to the combiner or finisher function, it
+ * is never passed to the accumulator function again.</li>
* <li>For non-concurrent collectors, any result returned from the result
* supplier, accumulator, or combiner functions must be serially
* thread-confined. This enables collection to occur in parallel without
@@ -132,11 +136,10 @@
* Performing a reduction operation with a {@code Collector} should produce a
* result equivalent to:
* <pre>{@code
- * BiFunction<R,T,R> accumulator = collector.accumulator();
- * R result = collector.resultSupplier().get();
+ * R container = collector.supplier().get();
* for (T t : data)
- * result = accumulator.apply(result, t);
- * return result;
+ * collector.accumulator().accept(container, t);
+ * return collector.finisher().apply(container);
* }</pre>
*
* <p>However, the library is free to partition the input, perform the reduction
@@ -149,7 +152,7 @@
* is accumulating elements into a {@code TreeSet}. In this case, the {@code
* resultSupplier()} function is {@code () -> new Treeset<T>()}, the
* {@code accumulator} function is
- * {@code (set, element) -> { set.add(element); return set; }}, and the combiner
+ * {@code (set, element) -> set.add(element) }, and the combiner
* function is {@code (left, right) -> { left.addAll(right); return left; }}.
* (This behavior is implemented by
* {@code Collectors.toCollection(TreeSet::new)}).
@@ -159,51 +162,49 @@
* @see Stream#collect(Collector)
* @see Collectors
*
- * @param <T> the type of input element to the collect operation
- * @param <R> the result type of the collect operation
+ * @param <T> the type of input elements to the reduction operation
+ * @param <A> the mutable accumulation type of the reduction operation (often
+ * hidden as an implementation detail)
+ * @param <R> the result type of the reduction operation
* @since 1.8
*/
-public interface Collector<T, R> {
+public interface Collector<T, A, R> {
/**
- * A function that creates and returns a new result that represents
- * "no values". If the accumulator or combiner functions may mutate their
- * arguments, this must be a new, empty result container.
+ * A function that creates and returns a new mutable result container.
*
- * @return a function which, when invoked, returns a result representing
- * "no values"
+ * @return a function which returns a new, mutable result container
*/
- Supplier<R> resultSupplier();
+ Supplier<A> supplier();
/**
- * A function that folds a new value into a cumulative result. The result
- * may be a mutable result container or a value. The accumulator function
- * may modify a mutable container and return it, or create a new result and
- * return that, but if it returns a new result object, it must not modify
- * any of its arguments.
+ * A function that folds a new value into a mutable result container.
*
- * <p>If the collector has the {@link Characteristics#STRICTLY_MUTATIVE}
- * characteristic, then the accumulator function <em>must</em> always return
- * its first argument, after possibly mutating its state.
- *
- * @return a function which folds a new value into a cumulative result
+ * @return a function which folds a new value into a mutable result container
*/
- BiFunction<R, T, R> accumulator();
+ BiConsumer<A, T> accumulator();
/**
* A function that accepts two partial results and merges them. The
* combiner function may fold state from one argument into the other and
- * return that, or may return a new result object, but if it returns
- * a new result object, it must not modify the state of either of its
- * arguments.
- *
- * <p>If the collector has the {@link Characteristics#STRICTLY_MUTATIVE}
- * characteristic, then the combiner function <em>must</em> always return
- * its first argument, after possibly mutating its state.
+ * return that, or may return a new result object.
*
* @return a function which combines two partial results into a cumulative
* result
*/
- BinaryOperator<R> combiner();
+ BinaryOperator<A> combiner();
+
+ /**
+ * Perform the final transformation from the intermediate accumulation type
+ * {@code A} to the final result representation {@code R}.
+ *
+ * <p>If the characteristic {@code IDENTITY_TRANSFORM} is
+ * set, this function may be presumed to be an identity transform with an
+ * unchecked cast from {@code A} to {@code R}.
+ *
+ * @return a function which transforms the intermediate result to the final
+ * result
+ */
+ Function<A, R> finisher();
/**
* Returns a {@code Set} of {@code Collector.Characteristics} indicating
@@ -214,6 +215,62 @@
Set<Characteristics> characteristics();
/**
+ * Returns a new {@code Collector} described by the given {@code supplier},
+ * {@code accumulator}, and {@code combiner} functions. The resulting
+ * {@code Collector} has the {@code Collector.Characteristics.IDENTITY_FINISH}
+ * characteristic.
+ *
+ * @param supplier The supplier function for the new collector
+ * @param accumulator The accumulator function for the new collector
+ * @param combiner The combiner function for the new collector
+ * @param characteristics The collector characteristics for the new
+ * collector
+ * @param <T> The type of input elements for the new collector
+ * @param <R> The type of intermediate accumulation result, and final result,
+ * for the new collector
+ * @return the new {@code Collector}
+ */
+ public static<T, R> Collector<T, R, R> of(Supplier<R> supplier,
+ BiConsumer<R, T> accumulator,
+ BinaryOperator<R> combiner,
+ Characteristics... characteristics) {
+ Set<Characteristics> cs = (characteristics.length == 0)
+ ? Collectors.CH_ID
+ : Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.IDENTITY_FINISH,
+ characteristics));
+ return new Collectors.CollectorImpl<>(supplier, accumulator, combiner, cs);
+ }
+
+ /**
+ * Returns a new {@code Collector} described by the given {@code supplier},
+ * {@code accumulator}, {@code combiner}, and {@code finisher} functions.
+ *
+ * @param supplier The supplier function for the new collector
+ * @param accumulator The accumulator function for the new collector
+ * @param combiner The combiner function for the new collector
+ * @param finisher The finisher function for the new collector
+ * @param characteristics The collector characteristics for the new
+ * collector
+ * @param <T> The type of input elements for the new collector
+ * @param <A> The intermediate accumulation type of the new collector
+ * @param <R> The final result type of the new collector
+ * @return the new {@code Collector}
+ */
+ public static<T, A, R> Collector<T, A, R> of(Supplier<A> supplier,
+ BiConsumer<A, T> accumulator,
+ BinaryOperator<A> combiner,
+ Function<A, R> finisher,
+ Characteristics... characteristics) {
+ Set<Characteristics> cs = Collectors.CH_NOID;
+ if (characteristics.length > 0) {
+ cs = EnumSet.noneOf(Characteristics.class);
+ Collections.addAll(cs, characteristics);
+ cs = Collections.unmodifiableSet(cs);
+ }
+ return new Collectors.CollectorImpl<>(supplier, accumulator, combiner, finisher, cs);
+ }
+
+ /**
* Characteristics indicating properties of a {@code Collector}, which can
* be used to optimize reduction implementations.
*/
@@ -222,8 +279,7 @@
* Indicates that this collector is <em>concurrent</em>, meaning that
* the result container can support the accumulator function being
* called concurrently with the same result container from multiple
- * threads. Concurrent collectors must also always have the
- * {@code STRICTLY_MUTATIVE} characteristic.
+ * threads.
*
* <p>If a {@code CONCURRENT} collector is not also {@code UNORDERED},
* then it should only be evaluated concurrently if applied to an
@@ -238,12 +294,10 @@
UNORDERED,
/**
- * Indicates that this collector operates by strict mutation of its
- * result container. This means that the {@link #accumulator()} and
- * {@link #combiner()} functions will always modify the state of and
- * return their first argument, rather than returning a different result
- * container.
+ * Indicates that the finisher function is the identity function and
+ * can be elided. If set, it must be the case that an unchecked cast
+ * from A to R will succeed.
*/
- STRICTLY_MUTATIVE
+ IDENTITY_FINISH
}
}
diff --git a/src/share/classes/java/util/stream/Collectors.java b/src/share/classes/java/util/stream/Collectors.java
index 8f5e8ff..29a5464 100644
--- a/src/share/classes/java/util/stream/Collectors.java
+++ b/src/share/classes/java/util/stream/Collectors.java
@@ -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.
- *
- * @implSpec
- * This produces a result equivalent to:
- * <pre>{@code
- * reducing(0L, mapper, Long::sum)
- * }</pre>
+ * 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, Long>
- sumBy(Function<? super T, Long> mapper) {
- return reducing(0L, mapper, Long::sum);
+ 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<T,T>} which performs a reduction of its
- * input elements under a specified {@code BinaryOperator}.
+ * 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.
+ *
+ * @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, ?, 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} 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;
+ A resultContainer = m.computeIfAbsent(key, k -> downstreamSupplier.get());
+ downstreamAccumulator.accept(resultContainer, t);
};
- return new CollectorImpl<>(mapFactory, accumulator, combiner, CH_CONCURRENT);
- } else if (downstream.characteristics().contains(Collector.Characteristics.STRICTLY_MUTATIVE)) {
- 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");
- D resultContainer = m.computeIfAbsent(key, k -> downstreamSupplier.get());
+ A resultContainer = m.computeIfAbsent(key, k -> downstreamSupplier.get());
synchronized (resultContainer) {
- downstreamAccumulator.apply(resultContainer, t);
+ downstreamAccumulator.accept(resultContainer, t);
}
- return m;
};
- return new CollectorImpl<>(mapFactory, accumulator, combiner, CH_CONCURRENT);
- } else {
- BiFunction<M, T, M> 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);
+ }
+
+ 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<>(mapFactory, accumulator, combiner, CH_CONCURRENT);
+ 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);
};
- return new CollectorImpl<>(() -> new Partition<>(downstream.resultSupplier().get(),
- downstream.resultSupplier().get()),
- accumulator, partitionMerger(downstream.combiner()), CH_STRICT);
+ 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));
+ };
+ 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
diff --git a/src/share/classes/java/util/stream/DelegatingStream.java b/src/share/classes/java/util/stream/DelegatingStream.java
index b3a0002..2dab1a4 100644
--- a/src/share/classes/java/util/stream/DelegatingStream.java
+++ b/src/share/classes/java/util/stream/DelegatingStream.java
@@ -209,7 +209,7 @@
}
@Override
- public <R> R collect(Collector<? super T, R> collector) {
+ public <R, A> R collect(Collector<? super T, A, ? extends R> collector) {
return delegate.collect(collector);
}
diff --git a/src/share/classes/java/util/stream/DoubleStream.java b/src/share/classes/java/util/stream/DoubleStream.java
index 50c9666..93a8399 100644
--- a/src/share/classes/java/util/stream/DoubleStream.java
+++ b/src/share/classes/java/util/stream/DoubleStream.java
@@ -527,7 +527,7 @@
long count();
/**
- * Returns an {@code OptionalDouble} describing the average of elements of
+ * Returns an {@code OptionalDouble} describing the arithmetic mean of elements of
* this stream, or an empty optional if this stream is empty. The average
* returned can vary depending upon the order in which elements are
* encountered. This is due to accumulated rounding error in addition of
diff --git a/src/share/classes/java/util/stream/IntStream.java b/src/share/classes/java/util/stream/IntStream.java
index ce515e9..883b03c 100644
--- a/src/share/classes/java/util/stream/IntStream.java
+++ b/src/share/classes/java/util/stream/IntStream.java
@@ -517,7 +517,7 @@
long count();
/**
- * Returns an {@code OptionalDouble} describing the average of elements of
+ * Returns an {@code OptionalDouble} describing the arithmetic mean of elements of
* this stream, or an empty optional if this stream is empty. This is a
* special case of a
* <a href="package-summary.html#MutableReduction">reduction</a>.
diff --git a/src/share/classes/java/util/stream/LongStream.java b/src/share/classes/java/util/stream/LongStream.java
index 39c4e1b..8fce0d6 100644
--- a/src/share/classes/java/util/stream/LongStream.java
+++ b/src/share/classes/java/util/stream/LongStream.java
@@ -517,7 +517,7 @@
long count();
/**
- * Returns an {@code OptionalDouble} describing the average of elements of
+ * Returns an {@code OptionalDouble} describing the arithmetic mean of elements of
* this stream, or an empty optional if this stream is empty. This is a
* special case of a
* <a href="package-summary.html#MutableReduction">reduction</a>.
diff --git a/src/share/classes/java/util/stream/ReduceOps.java b/src/share/classes/java/util/stream/ReduceOps.java
index 5a3361d..20d3336 100644
--- a/src/share/classes/java/util/stream/ReduceOps.java
+++ b/src/share/classes/java/util/stream/ReduceOps.java
@@ -148,17 +148,17 @@
* reference values.
*
* @param <T> the type of the input elements
- * @param <R> the type of the result
+ * @param <I> the type of the intermediate reduction result
* @param collector a {@code Collector} defining the reduction
* @return a {@code ReduceOp} implementing the reduction
*/
- public static <T,R> TerminalOp<T, R>
- makeRef(Collector<? super T,R> collector) {
- Supplier<R> supplier = Objects.requireNonNull(collector).resultSupplier();
- BiFunction<R, ? super T, R> accumulator = collector.accumulator();
- BinaryOperator<R> combiner = collector.combiner();
- class ReducingSink extends Box<R>
- implements AccumulatingSink<T, R, ReducingSink> {
+ public static <T, I> TerminalOp<T, I>
+ makeRef(Collector<? super T, I, ?> collector) {
+ Supplier<I> supplier = Objects.requireNonNull(collector).supplier();
+ BiConsumer<I, ? super T> accumulator = collector.accumulator();
+ BinaryOperator<I> combiner = collector.combiner();
+ class ReducingSink extends Box<I>
+ implements AccumulatingSink<T, I, ReducingSink> {
@Override
public void begin(long size) {
state = supplier.get();
@@ -166,9 +166,7 @@
@Override
public void accept(T t) {
- R newResult = accumulator.apply(state, t);
- if (state != newResult)
- state = newResult;
+ accumulator.accept(state, t);
}
@Override
@@ -176,7 +174,7 @@
state = combiner.apply(state, other.state);
}
}
- return new ReduceOp<T, R, ReducingSink>(StreamShape.REFERENCE) {
+ return new ReduceOp<T, I, ReducingSink>(StreamShape.REFERENCE) {
@Override
public ReducingSink makeSink() {
return new ReducingSink();
diff --git a/src/share/classes/java/util/stream/ReferencePipeline.java b/src/share/classes/java/util/stream/ReferencePipeline.java
index 8a86c2d..5e67b31 100644
--- a/src/share/classes/java/util/stream/ReferencePipeline.java
+++ b/src/share/classes/java/util/stream/ReferencePipeline.java
@@ -490,16 +490,21 @@
}
@Override
- public final <R> R collect(Collector<? super P_OUT, R> collector) {
+ public final <R, A> R collect(Collector<? super P_OUT, A, ? extends R> collector) {
+ A container;
if (isParallel()
&& (collector.characteristics().contains(Collector.Characteristics.CONCURRENT))
&& (!isOrdered() || collector.characteristics().contains(Collector.Characteristics.UNORDERED))) {
- R container = collector.resultSupplier().get();
- BiFunction<R, ? super P_OUT, R> accumulator = collector.accumulator();
- forEach(u -> accumulator.apply(container, u));
- return container;
+ container = collector.supplier().get();
+ BiConsumer<A, ? super P_OUT> accumulator = collector.accumulator();
+ forEach(u -> accumulator.accept(container, u));
}
- return evaluate(ReduceOps.makeRef(collector));
+ else {
+ container = evaluate(ReduceOps.makeRef(collector));
+ }
+ return collector.characteristics().contains(Collector.Characteristics.IDENTITY_FINISH)
+ ? (R) container
+ : collector.finisher().apply(container);
}
@Override
diff --git a/src/share/classes/java/util/stream/Stream.java b/src/share/classes/java/util/stream/Stream.java
index 76789d3..59d703b 100644
--- a/src/share/classes/java/util/stream/Stream.java
+++ b/src/share/classes/java/util/stream/Stream.java
@@ -651,12 +651,13 @@
* }</pre>
*
* @param <R> the type of the result
+ * @param <A> the intermediate accumulation type of the {@code Collector}
* @param collector the {@code Collector} describing the reduction
* @return the result of the reduction
* @see #collect(Supplier, BiConsumer, BiConsumer)
* @see Collectors
*/
- <R> R collect(Collector<? super T, R> collector);
+ <R, A> R collect(Collector<? super T, A, ? extends R> collector);
/**
* Returns the minimum element of this stream according to the provided
diff --git a/src/share/classes/java/util/stream/package-info.java b/src/share/classes/java/util/stream/package-info.java
index 39509ff..46d033e 100644
--- a/src/share/classes/java/util/stream/package-info.java
+++ b/src/share/classes/java/util/stream/package-info.java
@@ -547,7 +547,7 @@
* List<String> l = new ArrayList(Arrays.asList("one", "two"));
* Stream<String> sl = l.stream();
* l.add("three");
- * String s = sl.collect(toStringJoiner(" ")).toString();
+ * String s = sl.collect(joining(" "));
* }</pre>
* First a list is created consisting of two strings: "one"; and "two". Then a stream is created from that list.
* Next the list is modified by adding a third string: "three". Finally the elements of the stream are collected
@@ -557,7 +557,7 @@
* <pre>{@code
* List<String> l = new ArrayList(Arrays.asList("one", "two"));
* Stream<String> sl = l.stream();
- * String s = sl.peek(s -> l.add("BAD LAMBDA")).collect(toStringJoiner(" ")).toString();
+ * String s = sl.peek(s -> l.add("BAD LAMBDA")).collect(joining(" "));
* }</pre>
* then a {@code ConcurrentModificationException} will be thrown since the {@code peek} operation will attempt
* to add the string "BAD LAMBDA" to the list after the terminal operation has commenced.
diff --git a/test/java/util/stream/test/org/openjdk/tests/java/util/FillableStringTest.java b/test/java/util/stream/test/org/openjdk/tests/java/util/FillableStringTest.java
index 565d668..1e65e50 100644
--- a/test/java/util/stream/test/org/openjdk/tests/java/util/FillableStringTest.java
+++ b/test/java/util/stream/test/org/openjdk/tests/java/util/FillableStringTest.java
@@ -40,17 +40,17 @@
}
public void testStringBuilder() {
- String s = generate().collect(Collectors.toStringBuilder()).toString();
+ String s = generate().collect(Collectors.joining());
assertEquals(s, "THREEFOURFIVE");
}
public void testStringBuffer() {
- String s = generate().collect(Collectors.toStringBuilder()).toString();
+ String s = generate().collect(Collectors.joining());
assertEquals(s, "THREEFOURFIVE");
}
public void testStringJoiner() {
- String s = generate().collect(Collectors.toStringJoiner("-")).toString();
+ String s = generate().collect(Collectors.joining("-"));
assertEquals(s, "THREE-FOUR-FIVE");
}
}
diff --git a/test/java/util/stream/test/org/openjdk/tests/java/util/stream/GroupByOpTest.java b/test/java/util/stream/test/org/openjdk/tests/java/util/stream/GroupByOpTest.java
index ce48d27..dc9e197 100644
--- a/test/java/util/stream/test/org/openjdk/tests/java/util/stream/GroupByOpTest.java
+++ b/test/java/util/stream/test/org/openjdk/tests/java/util/stream/GroupByOpTest.java
@@ -36,7 +36,6 @@
import java.util.stream.LambdaTestHelpers;
import java.util.stream.OpTestCase;
import java.util.stream.Stream;
-import java.util.stream.StreamOpFlagTestHelper;
import java.util.stream.StreamTestDataProvider;
import java.util.stream.TestData;
@@ -59,13 +58,14 @@
public class GroupByOpTest extends OpTestCase {
public void testBypassCollect() {
- Collector<Integer, Map<Boolean, List<Integer>>> collector
- = Collectors.groupingBy(LambdaTestHelpers.forPredicate(pEven, true, false));
+ @SuppressWarnings("unchecked")
+ Collector<Integer, Map<Boolean, List<Integer>>, Map<Boolean, List<Integer>>> collector
+ = (Collector<Integer, Map<Boolean, List<Integer>>, Map<Boolean, List<Integer>>>) Collectors.groupingBy(LambdaTestHelpers.forPredicate(pEven, true, false));
- Map<Boolean, List<Integer>> m = collector.resultSupplier().get();
+ Map<Boolean, List<Integer>> m = collector.supplier().get();
int[] ints = countTo(10).stream().mapToInt(e -> (int) e).toArray();
for (int i : ints)
- m = collector.accumulator().apply(m, i);
+ collector.accumulator().accept(m, i);
assertEquals(2, m.keySet().size());
for(Collection<Integer> group : m.values()) {
@@ -130,7 +130,7 @@
// - Total number of values equals size of data
for (MapperData<Integer, ?> md : getMapperData(data)) {
- Collector<Integer, Map<Object, List<Integer>>> tab = Collectors.groupingBy(md.m);
+ Collector<Integer, ?, Map<Object, List<Integer>>> tab = Collectors.groupingBy(md.m);
Map<Object, List<Integer>> result =
withData(data)
.terminal(s -> s, s -> s.collect(tab))
diff --git a/test/java/util/stream/test/org/openjdk/tests/java/util/stream/SummaryStatisticsTest.java b/test/java/util/stream/test/org/openjdk/tests/java/util/stream/SummaryStatisticsTest.java
index fb5a92f..3f699de 100644
--- a/test/java/util/stream/test/org/openjdk/tests/java/util/stream/SummaryStatisticsTest.java
+++ b/test/java/util/stream/test/org/openjdk/tests/java/util/stream/SummaryStatisticsTest.java
@@ -43,9 +43,9 @@
public class SummaryStatisticsTest extends OpTestCase {
public void testIntStatistics() {
List<IntSummaryStatistics> instances = new ArrayList<>();
- instances.add(countTo(1000).stream().collect(Collectors.toIntSummaryStatistics(i -> i)));
+ instances.add(countTo(1000).stream().collect(Collectors.summarizingInt(i -> i)));
instances.add(countTo(1000).stream().mapToInt(i -> i).summaryStatistics());
- instances.add(countTo(1000).parallelStream().collect(Collectors.toIntSummaryStatistics(i -> i)));
+ instances.add(countTo(1000).parallelStream().collect(Collectors.summarizingInt(i -> i)));
instances.add(countTo(1000).parallelStream().mapToInt(i -> i).summaryStatistics());
for (IntSummaryStatistics stats : instances) {
@@ -58,9 +58,9 @@
public void testLongStatistics() {
List<LongSummaryStatistics> instances = new ArrayList<>();
- instances.add(countTo(1000).stream().collect(Collectors.toLongSummaryStatistics(i -> i)));
+ instances.add(countTo(1000).stream().collect(Collectors.summarizingLong(i -> i)));
instances.add(countTo(1000).stream().mapToLong(i -> i).summaryStatistics());
- instances.add(countTo(1000).parallelStream().collect(Collectors.toLongSummaryStatistics(i -> i)));
+ instances.add(countTo(1000).parallelStream().collect(Collectors.summarizingLong(i -> i)));
instances.add(countTo(1000).parallelStream().mapToLong(i -> i).summaryStatistics());
for (LongSummaryStatistics stats : instances) {
@@ -73,9 +73,9 @@
public void testDoubleStatistics() {
List<DoubleSummaryStatistics> instances = new ArrayList<>();
- instances.add(countTo(1000).stream().collect(Collectors.toDoubleSummaryStatistics(i -> i)));
+ instances.add(countTo(1000).stream().collect(Collectors.summarizingDouble(i -> i)));
instances.add(countTo(1000).stream().mapToDouble(i -> i).summaryStatistics());
- instances.add(countTo(1000).parallelStream().collect(Collectors.toDoubleSummaryStatistics(i -> i)));
+ instances.add(countTo(1000).parallelStream().collect(Collectors.summarizingDouble(i -> i)));
instances.add(countTo(1000).parallelStream().mapToDouble(i -> i).summaryStatistics());
for (DoubleSummaryStatistics stats : instances) {
diff --git a/test/java/util/stream/test/org/openjdk/tests/java/util/stream/TabulatorsTest.java b/test/java/util/stream/test/org/openjdk/tests/java/util/stream/TabulatorsTest.java
index b908741..7505cb1 100644
--- a/test/java/util/stream/test/org/openjdk/tests/java/util/stream/TabulatorsTest.java
+++ b/test/java/util/stream/test/org/openjdk/tests/java/util/stream/TabulatorsTest.java
@@ -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;
diff --git a/test/jdk/lambda/MethodReferenceTestInstanceMethod.java b/test/jdk/lambda/MethodReferenceTestInstanceMethod.java
index 40a64aa..12faf39 100644
--- a/test/jdk/lambda/MethodReferenceTestInstanceMethod.java
+++ b/test/jdk/lambda/MethodReferenceTestInstanceMethod.java
@@ -47,7 +47,7 @@
}
public void testStringBuffer() {
- String s = generate().collect(Collectors.toStringBuilder()).toString();
+ String s = generate().collect(Collectors.joining());
assertEquals(s, "THREEFOURFIVE");
}
diff --git a/test/jdk/lambda/separate/TestHarness.java b/test/jdk/lambda/separate/TestHarness.java
index 801fa48..9a4d067 100644
--- a/test/jdk/lambda/separate/TestHarness.java
+++ b/test/jdk/lambda/separate/TestHarness.java
@@ -119,7 +119,7 @@
Class stub = new Class(specimen.getName(), cm);
String params =
- Arrays.asList(args).stream().collect(Collectors.toStringJoiner(", ")).toString();
+ Arrays.asList(args).stream().collect(Collectors.joining(", ")).toString();
ConcreteMethod sm = new ConcreteMethod(
method.getReturnType(), method.getName(),
@@ -150,7 +150,7 @@
null, Arrays.asList((Method)method));
Class cstub = new Class(specimen.getName());
- String params = Arrays.asList(args).stream().collect(Collectors.toStringJoiner(", ")).toString();
+ String params = Arrays.asList(args).stream().collect(Collectors.joining(", ")).toString();
ConcreteMethod sm = new ConcreteMethod(
"int", SourceModel.stdMethodName,