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