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src/java.base/share/classes/java/util/stream/Collectors.java
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*** 1883,1892 ****
--- 1883,1964 ----
(r, t) -> r.accept(mapper.applyAsDouble(t)),
(l, r) -> { l.combine(r); return l; }, CH_ID);
}
/**
+ * Returns a {@code Collector} that passes the input elements to two specified collectors
+ * and merges their results with the specified merge function.
+ *
+ * <p>The resulting collector is {@link Collector.Characteristics#UNORDERED} if both supplied
+ * collectors are unordered and {@link Collector.Characteristics#CONCURRENT} if both supplied
+ * collectors are concurrent.
+ *
+ * @param <T> the type of the input elements
+ * @param <R1> the result type of the first collector
+ * @param <R2> the result type of the second collector
+ * @param <R> the final result type
+ * @param c1 the first collector
+ * @param c2 the second collector
+ * @param finisher the function which merges two results into the single one
+ * @return a {@code Collector} which aggregates the results of two supplied collectors.
+ * @since 11
+ */
+ public static <T, R1, R2, R>
+ Collector<T, ?, R> pairing(Collector<? super T, ?, R1> c1,
+ Collector<? super T, ?, R2> c2,
+ BiFunction<? super R1, ? super R2, ? extends R> finisher) {
+ return pairing0(c1, c2, finisher);
+ }
+
+ private static <T, A1, A2, R1, R2, R>
+ Collector<T, ?, R> pairing0(Collector<? super T, A1, R1> c1,
+ Collector<? super T, A2, R2> c2,
+ BiFunction<? super R1, ? super R2, ? extends R> finisher) {
+ Objects.requireNonNull(c1, "c1");
+ Objects.requireNonNull(c2, "c2");
+ Objects.requireNonNull(finisher, "finisher");
+ EnumSet<Collector.Characteristics> c = EnumSet.noneOf(Collector.Characteristics.class);
+ c.addAll(c1.characteristics());
+ c.retainAll(c2.characteristics());
+ c.remove(Collector.Characteristics.IDENTITY_FINISH);
+
+ Supplier<A1> c1Supplier = Objects.requireNonNull(c1.supplier(), "c1 supplier");
+ Supplier<A2> c2Supplier = Objects.requireNonNull(c2.supplier(), "c2 supplier");
+ BiConsumer<A1, ? super T> c1Accumulator = Objects.requireNonNull(c1.accumulator(), "c1 accumulator");
+ BiConsumer<A2, ? super T> c2Accumulator = Objects.requireNonNull(c2.accumulator(), "c2 accumulator");
+ BinaryOperator<A1> c1Combiner = Objects.requireNonNull(c1.combiner(), "c1 combiner");
+ BinaryOperator<A2> c2Combiner = Objects.requireNonNull(c2.combiner(), "c2 combiner");
+ Function<A1, R1> c1Finisher = Objects.requireNonNull(c1.finisher(), "c1 finisher");
+ Function<A2, R2> c2Finisher = Objects.requireNonNull(c2.finisher(), "c2 finisher");
+
+ class PairBox {
+ A1 left = c1Supplier.get();
+ A2 right = c2Supplier.get();
+
+ void add(T t) {
+ c1Accumulator.accept(left, t);
+ c2Accumulator.accept(right, t);
+ }
+
+ PairBox combine(PairBox other) {
+ left = c1Combiner.apply(left, other.left);
+ right = c2Combiner.apply(right, other.right);
+ return this;
+ }
+
+ R get() {
+ R1 r1 = c1Finisher.apply(left);
+ R2 r2 = c2Finisher.apply(right);
+ return finisher.apply(r1, r2);
+ }
+ }
+
+ return new CollectorImpl<>(PairBox::new, PairBox::add, PairBox::combine, PairBox::get,
+ Collections.unmodifiableSet(c));
+ }
+
+ /**
* Implementation class used by partitioningBy.
*/
private static final class Partition<T>
extends AbstractMap<Boolean, T>
implements Map<Boolean, T> {
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