1 /* 2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 package java.util; 26 27 import java.util.function.DoubleConsumer; 28 import java.util.stream.Collector; 29 30 /** 31 * A state object for collecting statistics such as count, min, max, sum, and 32 * average. 33 * 34 * <p>This class is designed to work with (though does not require) 35 * {@linkplain java.util.stream streams}. For example, you can compute 36 * summary statistics on a stream of doubles with: 37 * <pre> {@code 38 * DoubleSummaryStatistics stats = doubleStream.collect(DoubleSummaryStatistics::new, 39 * DoubleSummaryStatistics::accept, 40 * DoubleSummaryStatistics::combine); 41 * }</pre> 42 * 43 * <p>{@code DoubleSummaryStatistics} can be used as a 44 * {@linkplain java.util.stream.Stream#collect(Collector) reduction} 45 * target for a {@linkplain java.util.stream.Stream stream}. For example: 46 * 47 * <pre> {@code 48 * DoubleSummaryStatistics stats = people.stream() 49 * .collect(Collectors.summarizingDouble(Person::getWeight)); 50 *}</pre> 51 * 52 * This computes, in a single pass, the count of people, as well as the minimum, 53 * maximum, sum, and average of their weights. 54 * 55 * @implNote This implementation is not thread safe. However, it is safe to use 56 * {@link java.util.stream.Collectors#summarizingDouble(java.util.function.ToDoubleFunction) 57 * Collectors.toDoubleStatistics()} on a parallel stream, because the parallel 58 * implementation of {@link java.util.stream.Stream#collect Stream.collect()} 59 * provides the necessary partitioning, isolation, and merging of results for 60 * safe and efficient parallel execution. 61 * @since 1.8 62 */ 63 public class DoubleSummaryStatistics implements DoubleConsumer { 64 private long count; 65 private double sum; 66 private double min = Double.POSITIVE_INFINITY; 67 private double max = Double.NEGATIVE_INFINITY; 68 69 /** 70 * Construct an empty instance with zero count, zero sum, 71 * {@code Double.POSITIVE_INFINITY} min, {@code Double.NEGATIVE_INFINITY} 72 * max and zero average. 73 */ 74 public DoubleSummaryStatistics() { } 75 76 /** 77 * Records another value into the summary information. 78 * 79 * @param value the input value 80 */ 81 @Override 82 public void accept(double value) { 83 ++count; 84 sum += value; 85 min = Math.min(min, value); 86 max = Math.max(max, value); 87 } 88 89 /** 90 * Combines the state of another {@code DoubleSummaryStatistics} into this 91 * one. 92 * 93 * @param other another {@code DoubleSummaryStatistics} 94 * @throws NullPointerException if {@code other} is null 95 */ 96 public void combine(DoubleSummaryStatistics other) { 97 count += other.count; 98 sum += other.sum; 99 min = Math.min(min, other.min); 100 max = Math.max(max, other.max); 101 } 102 103 /** 104 * Return the count of values recorded. 105 * 106 * @return the count of values 107 */ 108 public final long getCount() { 109 return count; 110 } 111 112 /** 113 * Returns the sum of values recorded, or zero if no values have been 114 * recorded. 115 * 116 * If any recorded value is a NaN or the sum is at any point a NaN 117 * then the sum will be NaN. 118 * 119 * <p> The value of a floating-point sum is a function both of the 120 * input values as well as the order of addition operations. The 121 * order of addition operations of this method is intentionally 122 * not defined to allow for implementation flexibility to improve 123 * the speed and accuracy of the computed result. 124 * 125 * In particular, this method may be implemented using compensated 126 * summation or other technique to reduce the error bound in the 127 * numerical sum compared to a simple summation of {@code double} 128 * values. 129 * 130 * @apiNote Values sorted by increasing absolute magnitude tend to yield 131 * more accurate results. 132 * 133 * @return the sum of values, or zero if none 134 */ 135 public final double getSum() { 136 return sum; 137 } 138 139 /** 140 * Returns the minimum recorded value, {@code Double.NaN} if any recorded 141 * value was NaN or {@code Double.POSITIVE_INFINITY} if no values were 142 * recorded. Unlike the numerical comparison operators, this method 143 * considers negative zero to be strictly smaller than positive zero. 144 * 145 * @return the minimum recorded value, {@code Double.NaN} if any recorded 146 * value was NaN or {@code Double.POSITIVE_INFINITY} if no values were 147 * recorded 148 */ 149 public final double getMin() { 150 return min; 151 } 152 153 /** 154 * Returns the maximum recorded value, {@code Double.NaN} if any recorded 155 * value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were 156 * recorded. Unlike the numerical comparison operators, this method 157 * considers negative zero to be strictly smaller than positive zero. 158 * 159 * @return the maximum recorded value, {@code Double.NaN} if any recorded 160 * value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were 161 * recorded 162 */ 163 public final double getMax() { 164 return max; 165 } 166 167 /** 168 * Returns the arithmetic mean of values recorded, or zero if no 169 * values have been recorded. 170 * 171 * If any recorded value is a NaN or the sum is at any point a NaN 172 * then the average will be code NaN. 173 * 174 * <p>The average returned can vary depending upon the order in 175 * which values are recorded. 176 * 177 * This method may be implemented using compensated summation or 178 * other technique to reduce the error bound in the {@link #getSum 179 * numerical sum} used to compute the average. 180 * 181 * @apiNote Values sorted by increasing absolute magnitude tend to yield 182 * more accurate results. 183 * 184 * @return the arithmetic mean of values, or zero if none 185 */ 186 public final double getAverage() { 187 return getCount() > 0 ? getSum() / getCount() : 0.0d; 188 } 189 190 /** 191 * {@inheritDoc} 192 * 193 * Returns a non-empty string representation of this object suitable for 194 * debugging. The exact presentation format is unspecified and may vary 195 * between implementations and versions. 196 */ 197 @Override 198 public String toString() { 199 return String.format( 200 "%s{count=%d, sum=%f, min=%f, average=%f, max=%f}", 201 this.getClass().getSimpleName(), 202 getCount(), 203 getSum(), 204 getMin(), 205 getAverage(), 206 getMax()); 207 } 208 }