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.IntConsumer;
28 import java.util.function.LongConsumer;
29 import java.util.stream.Collector;
30
31 /**
32 * A state object for collecting statistics such as count, min, max, sum, and
33 * average.
34 *
35 * <p>This class is designed to work with (though does not require)
36 * {@linkplain java.util.stream streams}. For example, you can compute
37 * summary statistics on a stream of longs with:
38 * <pre> {@code
39 * LongSummaryStatistics stats = longStream.collect(LongSummaryStatistics::new,
40 * LongSummaryStatistics::accept,
41 * LongSummaryStatistics::combine);
42 * }</pre>
43 *
44 * <p>{@code LongSummaryStatistics} can be used as a
45 * {@linkplain java.util.stream.Stream#collect(Collector)} reduction}
46 * target for a {@linkplain java.util.stream.Stream stream}. For example:
47 *
48 * <pre> {@code
49 * LongSummaryStatistics stats = people.stream()
50 * .collect(Collectors.summarizingLong(Person::getAge));
51 *}</pre>
52 *
53 * This computes, in a single pass, the count of people, as well as the minimum,
54 * maximum, sum, and average of their ages.
55 *
56 * @implNote This implementation is not thread safe. However, it is safe to use
57 * {@link java.util.stream.Collectors#summarizingLong(java.util.function.ToLongFunction)
58 * Collectors.toLongStatistics()} on a parallel stream, because the parallel
59 * implementation of {@link java.util.stream.Stream#collect Stream.collect()}
60 * provides the necessary partitioning, isolation, and merging of results for
61 * safe and efficient parallel execution.
62 *
63 * <p>This implementation does not check for overflow of the sum.
64 * @since 1.8
65 */
66 public class LongSummaryStatistics implements LongConsumer, IntConsumer {
67 private long count;
68 private long sum;
69 private long min = Long.MAX_VALUE;
70 private long max = Long.MIN_VALUE;
71
72 /**
73 * Construct an empty instance with zero count, zero sum,
74 * {@code Long.MAX_VALUE} min, {@code Long.MIN_VALUE} max and zero
75 * average.
76 */
77 public LongSummaryStatistics() { }
78
79 /**
80 * Records a new {@code int} value into the summary information.
81 *
82 * @param value the input value
83 */
84 @Override
85 public void accept(int value) {
86 accept((long) value);
87 }
88
89 /**
90 * Records a new {@code long} value into the summary information.
91 *
92 * @param value the input value
93 */
94 @Override
95 public void accept(long value) {
96 ++count;
97 sum += value;
98 min = Math.min(min, value);
99 max = Math.max(max, value);
100 }
101
102 /**
103 * Combines the state of another {@code LongSummaryStatistics} into this
104 * one.
105 *
106 * @param other another {@code LongSummaryStatistics}
107 * @throws NullPointerException if {@code other} is null
108 */
109 public void combine(LongSummaryStatistics other) {
110 count += other.count;
111 sum += other.sum;
112 min = Math.min(min, other.min);
113 max = Math.max(max, other.max);
114 }
115
116 /**
117 * Returns the count of values recorded.
118 *
119 * @return the count of values
120 */
121 public final long getCount() {
122 return count;
123 }
124
125 /**
126 * Returns the sum of values recorded, or zero if no values have been
127 * recorded.
128 *
129 * @return the sum of values, or zero if none
130 */
131 public final long getSum() {
132 return sum;
133 }
134
135 /**
136 * Returns the minimum value recorded, or {@code Long.MAX_VALUE} if no
137 * values have been recorded.
138 *
139 * @return the minimum value, or {@code Long.MAX_VALUE} if none
140 */
141 public final long getMin() {
142 return min;
143 }
144
145 /**
146 * Returns the maximum value recorded, or {@code Long.MIN_VALUE} if no
147 * values have been recorded
148 *
149 * @return the maximum value, or {@code Long.MIN_VALUE} if none
150 */
151 public final long getMax() {
152 return max;
153 }
154
155 /**
156 * Returns the arithmetic mean of values recorded, or zero if no values have been
157 * recorded.
158 *
159 * @return The arithmetic mean of values, or zero if none
160 */
161 public final double getAverage() {
162 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d;
163 }
164
165 @Override
166 /**
167 * {@inheritDoc}
168 *
169 * Returns a non-empty string representation of this object suitable for
170 * debugging. The exact presentation format is unspecified and may vary
171 * between implementations and versions.
172 */
173 public String toString() {
174 return String.format(
175 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}",
176 this.getClass().getSimpleName(),
177 getCount(),
178 getSum(),
179 getMin(),
180 getAverage(),
181 getMax());
182 }
183 }