1 /*
2 * Copyright (c) 2012, 2019, 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.summarizingInt()} 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 count or 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 * Constructs 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 * Constructs a non-empty instance with the specified {@code count},
80 * {@code min}, {@code max}, and {@code sum}.
81 *
82 * <p>If {@code count} is zero then the remaining arguments are ignored and
83 * an empty instance is constructed.
84 *
85 * <p>If the arguments are inconsistent then an {@code IllegalArgumentException}
86 * is thrown. The necessary consistent argument conditions are:
87 * <ul>
88 * <li>{@code count >= 0}</li>
89 * <li>{@code min <= max}</li>
90 * </ul>
91 * @apiNote
92 * The enforcement of argument correctness means that the retrieved set of
93 * recorded values obtained from a {@code IntSummaryStatistics} source
94 * instance may not be a legal set of arguments for this constructor due to
95 * arithmetic overflow of the source's recorded count of values.
96 * The consistent argument conditions are not sufficient to prevent the
97 * creation of an internally inconsistent instance. An example of such a
98 * state would be an instance with: {@code count} = 2, {@code min} = 1,
99 * {@code max} = 2, and {@code sum} = 0.
100 *
101 * @param count the count of values
102 * @param min the minimum value
103 * @param max the maximum value
104 * @param sum the sum of all values
105 * @throws IllegalArgumentException if the arguments are inconsistent
106 * @since 10
107 */
108 public IntSummaryStatistics(long count, int min, int max, long sum)
109 throws IllegalArgumentException {
110 if (count < 0L) {
111 throw new IllegalArgumentException("Negative count value");
112 } else if (count > 0L) {
113 if (min > max) throw new IllegalArgumentException("Minimum greater than maximum");
114
115 this.count = count;
116 this.sum = sum;
117 this.min = min;
118 this.max = max;
119 }
120 // Use default field values if count == 0
121 }
122
123 /**
124 * Records a new value into the summary information
125 *
126 * @param value the input value
127 */
128 @Override
129 public void accept(int value) {
130 ++count;
131 sum += value;
132 min = Math.min(min, value);
133 max = Math.max(max, value);
134 }
135
136 /**
137 * Combines the state of another {@code IntSummaryStatistics} into this one.
138 *
139 * @param other another {@code IntSummaryStatistics}
140 * @throws NullPointerException if {@code other} is null
141 */
142 public void combine(IntSummaryStatistics other) {
143 count += other.count;
144 sum += other.sum;
145 min = Math.min(min, other.min);
146 max = Math.max(max, other.max);
147 }
148
149 /**
150 * Returns the count of values recorded.
151 *
152 * @return the count of values
153 */
154 public final long getCount() {
155 return count;
156 }
157
158 /**
159 * Returns the sum of values recorded, or zero if no values have been
160 * recorded.
161 *
162 * @return the sum of values, or zero if none
163 */
164 public final long getSum() {
165 return sum;
166 }
167
168 /**
169 * Returns the minimum value recorded, or {@code Integer.MAX_VALUE} if no
170 * values have been recorded.
171 *
172 * @return the minimum value, or {@code Integer.MAX_VALUE} if none
173 */
174 public final int getMin() {
175 return min;
176 }
177
178 /**
179 * Returns the maximum value recorded, or {@code Integer.MIN_VALUE} if no
180 * values have been recorded.
181 *
182 * @return the maximum value, or {@code Integer.MIN_VALUE} if none
183 */
184 public final int getMax() {
185 return max;
186 }
187
188 /**
189 * Returns the arithmetic mean of values recorded, or zero if no values have been
190 * recorded.
191 *
192 * @return the arithmetic mean of values, or zero if none
193 */
194 public final double getAverage() {
195 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d;
196 }
197
198 /**
199 * Returns a non-empty string representation of this object suitable for
200 * debugging. The exact presentation format is unspecified and may vary
201 * between implementations and versions.
202 */
203 @Override
204 public String toString() {
205 return String.format(
206 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}",
207 this.getClass().getSimpleName(),
208 getCount(),
209 getSum(),
210 getMin(),
211 getAverage(),
212 getMax());
213 }
214 }