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. The sum returned can vary depending upon the order in which 115 * values are recorded. This is due to accumulated rounding error in 116 * addition of values of differing magnitudes. Values sorted by increasing 117 * absolute magnitude tend to yield more accurate results. If any recorded 118 * value is a {@code NaN} or the sum is at any point a {@code NaN} then the 119 * sum will be {@code NaN}. 120 * 121 * @return the sum of values, or zero if none 122 */ 123 public final double getSum() { 124 return sum; 125 } 126 127 /** 128 * Returns the minimum recorded value, {@code Double.NaN} if any recorded 129 * value was NaN or {@code Double.POSITIVE_INFINITY} if no values were 130 * recorded. Unlike the numerical comparison operators, this method 131 * considers negative zero to be strictly smaller than positive zero. 132 * 133 * @return the minimum recorded value, {@code Double.NaN} if any recorded 134 * value was NaN or {@code Double.POSITIVE_INFINITY} if no values were 135 * recorded 136 */ 137 public final double getMin() { 138 return min; 139 } 140 141 /** 142 * Returns the maximum recorded value, {@code Double.NaN} if any recorded 143 * value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were 144 * recorded. Unlike the numerical comparison operators, this method 145 * considers negative zero to be strictly smaller than positive zero. 146 * 147 * @return the maximum recorded value, {@code Double.NaN} if any recorded 148 * value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were 149 * recorded 150 */ 151 public final double getMax() { 152 return max; 153 } 154 155 /** 156 * Returns the arithmetic mean of values recorded, or zero if no values have been 157 * recorded. The average returned can vary depending upon the order in 158 * which values are recorded. This is due to accumulated rounding error in 159 * addition of values of differing magnitudes. Values sorted by increasing 160 * absolute magnitude tend to yield more accurate results. If any recorded 161 * value is a {@code NaN} or the sum is at any point a {@code NaN} then the 162 * average will be {@code NaN}. 163 * 164 * @return the arithmetic mean of values, or zero if none 165 */ 166 public final double getAverage() { 167 return getCount() > 0 ? getSum() / getCount() : 0.0d; 168 } 169 170 /** 171 * {@inheritDoc} 172 * 173 * Returns a non-empty string representation of this object suitable for 174 * debugging. The exact presentation format is unspecified and may vary 175 * between implementations and versions. 176 */ 177 @Override 178 public String toString() { 179 return String.format( 180 "%s{count=%d, sum=%f, min=%f, average=%f, max=%f}", 181 this.getClass().getSimpleName(), 182 getCount(), 183 getSum(), 184 getMin(), 185 getAverage(), 186 getMax()); 187 } 188 }