--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/java.base/share/classes/java/util/DoubleSummaryStatistics.java Sun Aug 17 15:54:13 2014 +0100
@@ -0,0 +1,262 @@
+/*
+ * Copyright (c) 2012, 2014, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package java.util;
+
+import java.util.function.DoubleConsumer;
+import java.util.stream.Collector;
+
+/**
+ * A state object for collecting statistics such as count, min, max, sum, and
+ * average.
+ *
+ * <p>This class is designed to work with (though does not require)
+ * {@linkplain java.util.stream streams}. For example, you can compute
+ * summary statistics on a stream of doubles with:
+ * <pre> {@code
+ * DoubleSummaryStatistics stats = doubleStream.collect(DoubleSummaryStatistics::new,
+ * DoubleSummaryStatistics::accept,
+ * DoubleSummaryStatistics::combine);
+ * }</pre>
+ *
+ * <p>{@code DoubleSummaryStatistics} can be used as a
+ * {@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.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#summarizingDouble(java.util.function.ToDoubleFunction)
+ * Collectors.summarizingDouble()} 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
+ * safe and efficient parallel execution.
+ * @since 1.8
+ */
+public class DoubleSummaryStatistics implements DoubleConsumer {
+ private long count;
+ private double sum;
+ private double sumCompensation; // Low order bits of sum
+ private double simpleSum; // Used to compute right sum for non-finite inputs
+ private double min = Double.POSITIVE_INFINITY;
+ private double max = Double.NEGATIVE_INFINITY;
+
+ /**
+ * Construct an empty instance with zero count, zero sum,
+ * {@code Double.POSITIVE_INFINITY} min, {@code Double.NEGATIVE_INFINITY}
+ * max and zero average.
+ */
+ public DoubleSummaryStatistics() { }
+
+ /**
+ * Records another value into the summary information.
+ *
+ * @param value the input value
+ */
+ @Override
+ public void accept(double value) {
+ ++count;
+ simpleSum += value;
+ sumWithCompensation(value);
+ min = Math.min(min, value);
+ max = Math.max(max, value);
+ }
+
+ /**
+ * Combines the state of another {@code DoubleSummaryStatistics} into this
+ * one.
+ *
+ * @param other another {@code DoubleSummaryStatistics}
+ * @throws NullPointerException if {@code other} is null
+ */
+ public void combine(DoubleSummaryStatistics other) {
+ count += other.count;
+ simpleSum += other.simpleSum;
+ sumWithCompensation(other.sum);
+ sumWithCompensation(other.sumCompensation);
+ min = Math.min(min, other.min);
+ max = Math.max(max, other.max);
+ }
+
+ /**
+ * Incorporate a new double value using Kahan summation /
+ * compensated summation.
+ */
+ private void sumWithCompensation(double value) {
+ double tmp = value - sumCompensation;
+ double velvel = sum + tmp; // Little wolf of rounding error
+ sumCompensation = (velvel - sum) - tmp;
+ sum = velvel;
+ }
+
+ /**
+ * Return the count of values recorded.
+ *
+ * @return the count of values
+ */
+ public final long getCount() {
+ return count;
+ }
+
+ /**
+ * Returns the sum of values recorded, or zero if no values have been
+ * recorded.
+ *
+ * <p> The value of a floating-point sum is a function both of the
+ * input values as well as the order of addition operations. The
+ * order of addition operations of this method is intentionally
+ * not defined to allow for implementation flexibility to improve
+ * the speed and accuracy of the computed result.
+ *
+ * In particular, this method may be implemented using compensated
+ * summation or other technique to reduce the error bound in the
+ * numerical sum compared to a simple summation of {@code double}
+ * values.
+ *
+ * Because of the unspecified order of operations and the
+ * possibility of using differing summation schemes, the output of
+ * this method may vary on the same input values.
+ *
+ * <p>Various conditions can result in a non-finite sum being
+ * computed. This can occur even if the all the recorded values
+ * being summed are finite. If any recorded value is non-finite,
+ * the sum will be non-finite:
+ *
+ * <ul>
+ *
+ * <li>If any recorded value is a NaN, then the final sum will be
+ * NaN.
+ *
+ * <li>If the recorded values contain one or more infinities, the
+ * sum will be infinite or NaN.
+ *
+ * <ul>
+ *
+ * <li>If the recorded values contain infinities of opposite sign,
+ * the sum will be NaN.
+ *
+ * <li>If the recorded values contain infinities of one sign and
+ * an intermediate sum overflows to an infinity of the opposite
+ * sign, the sum may be NaN.
+ *
+ * </ul>
+ *
+ * </ul>
+ *
+ * It is possible for intermediate sums of finite values to
+ * overflow into opposite-signed infinities; if that occurs, the
+ * final sum will be NaN even if the recorded values are all
+ * finite.
+ *
+ * If all the recorded values are zero, the sign of zero is
+ * <em>not</em> guaranteed to be preserved in the final sum.
+ *
+ * @apiNote Values sorted by increasing absolute magnitude tend to yield
+ * more accurate results.
+ *
+ * @return the sum of values, or zero if none
+ */
+ public final double getSum() {
+ // Better error bounds to add both terms as the final sum
+ double tmp = sum + sumCompensation;
+ if (Double.isNaN(tmp) && Double.isInfinite(simpleSum))
+ // If the compensated sum is spuriously NaN from
+ // accumulating one or more same-signed infinite values,
+ // return the correctly-signed infinity stored in
+ // simpleSum.
+ return simpleSum;
+ else
+ return tmp;
+ }
+
+ /**
+ * Returns the minimum recorded value, {@code Double.NaN} if any recorded
+ * value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
+ * recorded. Unlike the numerical comparison operators, this method
+ * considers negative zero to be strictly smaller than positive zero.
+ *
+ * @return the minimum recorded value, {@code Double.NaN} if any recorded
+ * value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
+ * recorded
+ */
+ public final double getMin() {
+ return min;
+ }
+
+ /**
+ * Returns the maximum recorded value, {@code Double.NaN} if any recorded
+ * value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
+ * recorded. Unlike the numerical comparison operators, this method
+ * considers negative zero to be strictly smaller than positive zero.
+ *
+ * @return the maximum recorded value, {@code Double.NaN} if any recorded
+ * value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
+ * recorded
+ */
+ public final double getMax() {
+ return max;
+ }
+
+ /**
+ * Returns the arithmetic mean of values recorded, or zero if no
+ * values have been recorded.
+ *
+ * <p> The computed average can vary numerically and have the
+ * special case behavior as computing the sum; see {@link #getSum}
+ * for details.
+ *
+ * @apiNote Values sorted by increasing absolute magnitude tend to yield
+ * more accurate results.
+ *
+ * @return the arithmetic mean of values, or zero if none
+ */
+ public final double getAverage() {
+ return getCount() > 0 ? getSum() / getCount() : 0.0d;
+ }
+
+ /**
+ * {@inheritDoc}
+ *
+ * Returns a non-empty string representation of this object suitable for
+ * debugging. The exact presentation format is unspecified and may vary
+ * between implementations and versions.
+ */
+ @Override
+ public String toString() {
+ return String.format(
+ "%s{count=%d, sum=%f, min=%f, average=%f, max=%f}",
+ this.getClass().getSimpleName(),
+ getCount(),
+ getSum(),
+ getMin(),
+ getAverage(),
+ getMax());
+ }
+}