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
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 ints with:
36 * <pre> {@code
37 * IntSummaryStatistics stats = intStream.collect(IntSummaryStatistics::new,
38 * IntSummaryStatistics::accept,
39 * IntSummaryStatistics::combine);
40 * }</pre>
41 *
42 * <p>{@code IntSummaryStatistics} 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 * IntSummaryStatistics stats = people.stream()
48 * .collect(Collectors.toIntSummaryStatistics(Person::getDependents));
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 number of dependents.
53 *
54 * @implNote This implementation is not thread safe. However, it is safe to use
55 * {@link java.util.stream.Collectors#toIntSummaryStatistics(java.util.function.ToIntFunction)
56 * Collectors.toIntStatistics()} 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 *
61 * <p>This implementation does not check for overflow of the sum.
62 * @since 1.8
63 */
64 public class IntSummaryStatistics implements IntConsumer {
65 private long count;
66 private long sum;
67 private int min = Integer.MAX_VALUE;
68 private int max = Integer.MIN_VALUE;
69
70 /**
71 * Construct an empty instance with zero count, zero sum,
72 * {@code Integer.MAX_VALUE} min, {@code Integer.MIN_VALUE} max and zero
73 * average.
74 */
75 public IntSummaryStatistics() { }
76
77 /**
78 * Records a new value into the summary information
79 *
80 * @param value the input value
81 */
82 @Override
83 public void accept(int value) {
84 ++count;
85 sum += value;
86 min = Math.min(min, value);
87 max = Math.max(max, value);
88 }
89
90 /**
91 * Combines the state of another {@code IntSummaryStatistics} into this one.
92 *
93 * @param other another {@code IntSummaryStatistics}
94 * @throws NullPointerException if {@code other} is null
95 */
96 public void combine(IntSummaryStatistics 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 * Returns 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 * @return the sum of values, or zero if none
117 */
118 public final long getSum() {
119 return sum;
120 }
121
122 /**
123 * Returns the minimum value recorded, or {@code Integer.MAX_VALUE} if no
124 * values have been recorded.
125 *
126 * @return the minimum value, or {@code Integer.MAX_VALUE} if none
127 */
128 public final int getMin() {
129 return min;
130 }
131
132 /**
133 * Returns the maximum value recorded, or {@code Integer.MIN_VALUE} if no
134 * values have been recorded.
135 *
136 * @return the maximum value, or {@code Integer.MIN_VALUE} if none
137 */
138 public final int getMax() {
139 return max;
140 }
141
142 /**
143 * Returns the average of values recorded, or zero if no values have been
144 * recorded.
145 *
146 * @return the average of values, or zero if none
147 */
148 public final double getAverage() {
149 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d;
150 }
151
152 @Override
153 /**
154 * {@inheritDoc}
155 *
156 * Returns a non-empty string representation of this object suitable for
157 * debugging. The exact presentation format is unspecified and may vary
158 * between implementations and versions.
159 */
160 public String toString() {
161 return String.format(
162 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}",
163 this.getClass().getSimpleName(),
164 getCount(),
165 getSum(),
166 getMin(),
167 getAverage(),
168 getMax());
169 }
170 }