src/share/classes/java/util/stream/Collectors.java

*** 504,519 ****
       * @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<>(
!                 () -> 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.
       *
--- 504,541 ----
       * @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<>(
!                 () -> new double[2],
!                 (a, t) -> { sumWithCompensation(a, mapper.applyAsDouble(t)); },
!                 (a, b) -> { sumWithCompensation(a, b[0]); return sumWithCompensation(a, b[1]); },
!                 a -> a[0],
!                 CH_NOID);
!     }
! 
!     /**
!      * Incorporate a new double value using Kahan summation /
!      * compensation summation.
!      *
!      * High-order bits of the sum are in intermediateSum[0], low-order
!      * bits of the sum are in intermediateSum[1], any additional
!      * elements are application-specific.
!      *
!      * @param intermediateSum the high-order and low-order words of the intermediate sum
!      * @param value the name value to be included in the running sum
!      */
!     static double[] sumWithCompensation(double[] intermediateSum, double value) {
!         double tmp = value - intermediateSum[1];
!         double sum = intermediateSum[0];
!         double velvel = sum + tmp; // Little wolf of rounding error
!         intermediateSum[1] = (velvel - sum) - tmp;
!         intermediateSum[0] = velvel;
!         return intermediateSum;
      }
  
+ 
      /**
       * 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.
       *
*** 565,578 ****
       * @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<>(
!                 () -> 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
--- 587,601 ----
       * @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<>(
!                 () -> new double[3],
!                 (a, t) -> { sumWithCompensation(a, mapper.applyAsDouble(t)); a[2]++; },
!                 (a, b) -> { sumWithCompensation(a, b[0]); sumWithCompensation(a, b[1]); a[2] += b[2]; return a; },
!                 a -> (a[2] == 0) ? 0.0d : (a[0] / a[2]),
!                 CH_NOID);
      }
  
      /**
       * Returns a {@code Collector} which performs a reduction of its
       * input elements under a specified {@code BinaryOperator} using the