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 }