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 * Construct an empty instance with zero count, zero sum,
73 * {@code Long.MAX_VALUE} min, {@code Long.MIN_VALUE} max and zero
74 * average.
75 */
76 public LongSummaryStatistics() { }
77
78 /**
79 * Records a new {@code int} value into the summary information.
80 *
81 * @param value the input value
82 */
83 @Override
84 public void accept(int value) {
85 accept((long) value);
86 }
87
88 /**
89 * Records a new {@code long} value into the summary information.
90 *
91 * @param value the input value
92 */
93 @Override
94 public void accept(long value) {
95 ++count;
96 sum += value;
97 min = Math.min(min, value);
98 max = Math.max(max, value);
99 }
100
101 /**
102 * Combines the state of another {@code LongSummaryStatistics} into this
103 * one.
104 *
105 * @param other another {@code LongSummaryStatistics}
106 * @throws NullPointerException if {@code other} is null
107 */
108 public void combine(LongSummaryStatistics other) {
109 count += other.count;
110 sum += other.sum;
111 min = Math.min(min, other.min);
112 max = Math.max(max, other.max);
113 }
114
115 /**
116 * Returns the count of values recorded.
117 *
118 * @return the count of values
119 */
120 public final long getCount() {
121 return count;
122 }
123
124 /**
125 * Returns the sum of values recorded, or zero if no values have been
126 * recorded.
127 *
128 * @return the sum of values, or zero if none
129 */
130 public final long getSum() {
131 return sum;
132 }
133
134 /**
135 * Returns the minimum value recorded, or {@code Long.MAX_VALUE} if no
136 * values have been recorded.
137 *
138 * @return the minimum value, or {@code Long.MAX_VALUE} if none
139 */
140 public final long getMin() {
141 return min;
142 }
143
144 /**
145 * Returns the maximum value recorded, or {@code Long.MIN_VALUE} if no
146 * values have been recorded
147 *
148 * @return the maximum value, or {@code Long.MIN_VALUE} if none
149 */
150 public final long getMax() {
151 return max;
152 }
153
154 /**
155 * Returns the average of values recorded, or zero if no values have been
156 * recorded.
157 *
158 * @return The average of values, or zero if none
159 */
160 public final double getAverage() {
161 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d;
162 }
163
164 @Override
165 /**
166 * {@inheritDoc}
167 *
168 * Returns a non-empty string representation of this object suitable for
169 * debugging. The exact presentation format is unspecified and may vary
170 * between implementations and versions.
171 */
172 public String toString() {
173 return String.format(
174 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}",
175 this.getClass().getSimpleName(),
176 getCount(),
177 getSum(),
178 getMin(),
179 getAverage(),
180 getMax());
181 }
182 }