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