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
29 /**
30 * A state object for collecting statistics such as count, min, max, sum, and
31 * average.
32 *
33 * <p>This class is designed to work with (though does not require)
34 * {@linkplain java.util.stream streams}. For example, you can compute
35 * summary statistics on a stream of doubles with:
36 * <pre> {@code
37 * DoubleSummaryStatistics stats = doubleStream.collect(DoubleSummaryStatistics::new,
38 * DoubleSummaryStatistics::accept,
39 * DoubleSummaryStatistics::combine);
40 * }</pre>
41 *
42 * <p>{@code DoubleSummaryStatistics} can be used as a
43 * {@linkplain java.util.stream.Stream#reduce(java.util.function.BinaryOperator) reduction}
44 * target for a {@linkplain java.util.stream.Stream stream}. For example:
45 *
46 * <pre> {@code
47 * DoubleSummaryStatistics stats = people.stream()
48 * .collect(Collectors.toDoubleSummaryStatistics(Person::getWeight));
49 *}</pre>
50 *
51 * This computes, in a single pass, the count of people, as well as the minimum,
52 * maximum, sum, and average of their weights.
53 *
54 * @implNote This implementation is not thread safe. However, it is safe to use
55 * {@link java.util.stream.Collectors#toDoubleSummaryStatistics(java.util.function.ToDoubleFunction)
56 * Collectors.toDoubleStatistics()} on a parallel stream, because the parallel
57 * implementation of {@link java.util.stream.Stream#collect Stream.collect()}
58 * provides the necessary partitioning, isolation, and merging of results for
59 * safe and efficient parallel execution.
60 * @since 1.8
61 */
62 public class DoubleSummaryStatistics implements DoubleConsumer {
63 private long count;
64 private double sum;
65 private double min = Double.POSITIVE_INFINITY;
66 private double max = Double.NEGATIVE_INFINITY;
67
68 /**
69 * Construct an empty instance with zero count, zero sum,
70 * {@code Double.POSITIVE_INFINITY} min, {@code Double.NEGATIVE_INFINITY}
71 * max and zero average.
72 */
73 public DoubleSummaryStatistics() { }
74
75 /**
76 * Records another value into the summary information.
77 *
78 * @param value the input value
79 */
80 @Override
81 public void accept(double value) {
82 ++count;
83 sum += value;
84 min = Math.min(min, value);
85 max = Math.max(max, value);
86 }
87
88 /**
89 * Combines the state of another {@code DoubleSummaryStatistics} into this
90 * one.
91 *
92 * @param other another {@code DoubleSummaryStatistics}
93 * @throws NullPointerException if {@code other} is null
94 */
95 public void combine(DoubleSummaryStatistics other) {
96 count += other.count;
97 sum += other.sum;
98 min = Math.min(min, other.min);
99 max = Math.max(max, other.max);
100 }
101
102 /**
103 * Return the count of values recorded.
104 *
105 * @return the count of values
106 */
107 public final long getCount() {
108 return count;
109 }
110
111 /**
112 * Returns the sum of values recorded, or zero if no values have been
113 * recorded. The sum returned can vary depending upon the order in which
114 * values are recorded. This is due to accumulated rounding error in
115 * addition of values of differing magnitudes. Values sorted by increasing
116 * absolute magnitude tend to yield more accurate results. If any recorded
117 * value is a {@code NaN} or the sum is at any point a {@code NaN} then the
118 * sum will be {@code NaN}.
119 *
120 * @return the sum of values, or zero if none
121 */
122 public final double getSum() {
123 return sum;
124 }
125
126 /**
127 * Returns the minimum recorded value, {@code Double.NaN} if any recorded
128 * value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
129 * recorded. Unlike the numerical comparison operators, this method
130 * considers negative zero to be strictly smaller than positive zero.
131 *
132 * @return the minimum recorded value, {@code Double.NaN} if any recorded
133 * value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
134 * recorded
135 */
136 public final double getMin() {
137 return min;
138 }
139
140 /**
141 * Returns the maximum recorded value, {@code Double.NaN} if any recorded
142 * value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
143 * recorded. Unlike the numerical comparison operators, this method
144 * considers negative zero to be strictly smaller than positive zero.
145 *
146 * @return the maximum recorded value, {@code Double.NaN} if any recorded
147 * value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
148 * recorded
149 */
150 public final double getMax() {
151 return max;
152 }
153
154 /**
155 * Returns the average of values recorded, or zero if no values have been
156 * recorded. The average returned can vary depending upon the order in
157 * which values are recorded. This is due to accumulated rounding error in
158 * addition of values of differing magnitudes. Values sorted by increasing
159 * absolute magnitude tend to yield more accurate results. If any recorded
160 * value is a {@code NaN} or the sum is at any point a {@code NaN} then the
161 * average will be {@code NaN}.
162 *
163 * @return the average of values, or zero if none
164 */
165 public final double getAverage() {
166 return getCount() > 0 ? getSum() / getCount() : 0.0d;
167 }
168
169 /**
170 * {@inheritDoc}
171 *
172 * Returns a non-empty string representation of this object suitable for
173 * debugging. The exact presentation format is unspecified and may vary
174 * between implementations and versions.
175 */
176 @Override
177 public String toString() {
178 return String.format(
179 "%s{count=%d, sum=%f, min=%f, average=%f, max=%f}",
180 this.getClass().getSimpleName(),
181 getCount(),
182 getSum(),
183 getMin(),
184 getAverage(),
185 getMax());
186 }
187 }