1 /*
2 * Copyright (c) 2012, 2017, 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
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23 * questions.
24 */
25 package java.util;
26
27 import java.util.function.IntConsumer;
28 import java.util.function.LongConsumer;
29 import java.util.stream.Collector;
30
31 /**
32 * A state object for collecting statistics such as count, min, max, sum, and
33 * average.
34 *
35 * <p>This class is designed to work with (though does not require)
36 * {@linkplain java.util.stream streams}. For example, you can compute
37 * summary statistics on a stream of longs with:
38 * <pre> {@code
39 * LongSummaryStatistics stats = longStream.collect(LongSummaryStatistics::new,
40 * LongSummaryStatistics::accept,
41 * LongSummaryStatistics::combine);
42 * }</pre>
43 *
44 * <p>{@code LongSummaryStatistics} can be used as a
45 * {@linkplain java.util.stream.Stream#collect(Collector) reduction}
46 * target for a {@linkplain java.util.stream.Stream stream}. For example:
47 *
48 * <pre> {@code
49 * LongSummaryStatistics stats = people.stream()
50 * .collect(Collectors.summarizingLong(Person::getAge));
51 *}</pre>
52 *
53 * This computes, in a single pass, the count of people, as well as the minimum,
54 * maximum, sum, and average of their ages.
55 *
56 * @implNote This implementation is not thread safe. However, it is safe to use
57 * {@link java.util.stream.Collectors#summarizingLong(java.util.function.ToLongFunction)
58 * Collectors.summarizingLong()} on a parallel stream, because the parallel
59 * implementation of {@link java.util.stream.Stream#collect Stream.collect()}
60 * provides the necessary partitioning, isolation, and merging of results for
61 * safe and efficient parallel execution.
62 *
63 * <p>This implementation does not check for overflow of the sum.
64 * @since 1.8
65 */
66 public class LongSummaryStatistics implements LongConsumer, IntConsumer {
67 private long count;
68 private long sum;
69 private long min = Long.MAX_VALUE;
70 private long max = Long.MIN_VALUE;
71
72 /**
73 * Constructs an empty instance with zero count, zero sum,
74 * {@code Long.MAX_VALUE} min, {@code Long.MIN_VALUE} max and zero
75 * average.
76 */
77 public LongSummaryStatistics() { }
78
79 /**
80 * Constructs a non-empty instance with the specified {@code count},
81 * {@code min}, {@code max}, and {@code sum}.
82 *
83 * <p>If {@code count} is zero then the remaining arguments are ignored and
84 * an empty instance is constructed.
85 *
86 * <p>If the arguments are inconsistent then an {@code IllegalArgumentException}
87 * is thrown. The necessary consistent argument conditions are:
88 * <ul>
89 * <li>{@code count >= 0}</li>
90 * <li>{@code min <= max}</li>
91 * </ul>
92 * @apiNote
93 * The enforcement of argument correctness means that the retrieved set of
94 * recorded values obtained from a {@code LongSummaryStatistics} source
95 * instance may not be a legal set of arguments for this constructor due to
96 * arithmetic overflow of the source's recorded count of values.
97 * The consistent argument conditions are not sufficient to prevent the
98 * creation of an internally inconsistent instance. An example of such a
99 * state would be an instance with: {@code count} = 2, {@code min} = 1,
100 * {@code max} = 2, and {@code sum} = 0.
101 *
102 * @param count the count of values
103 * @param min the minimum value
104 * @param max the maximum value
105 * @param sum the sum of all values
106 * @throws IllegalArgumentException if the arguments are inconsistent
107 * @since 10
108 */
109 public LongSummaryStatistics(long count, long min, long max, long sum)
110 throws IllegalArgumentException {
111 if (count < 0L) {
112 throw new IllegalArgumentException("Negative count value");
113 } else if (count > 0L) {
114 if (min > max) throw new IllegalArgumentException("Minimum greater than maximum");
115
116 this.count = count;
117 this.sum = sum;
118 this.min = min;
119 this.max = max;
120 }
121 // Use default field values if count == 0
122 }
123
124 /**
125 * Records a new {@code int} value into the summary information.
126 *
127 * @param value the input value
128 */
129 @Override
130 public void accept(int value) {
131 accept((long) value);
132 }
133
134 /**
135 * Records a new {@code long} value into the summary information.
136 *
137 * @param value the input value
138 */
139 @Override
140 public void accept(long value) {
141 ++count;
142 sum += value;
143 min = Math.min(min, value);
144 max = Math.max(max, value);
145 }
146
147 /**
148 * Combines the state of another {@code LongSummaryStatistics} into this
149 * one.
150 *
151 * @param other another {@code LongSummaryStatistics}
152 * @throws NullPointerException if {@code other} is null
153 */
154 public void combine(LongSummaryStatistics other) {
155 count += other.count;
156 sum += other.sum;
157 min = Math.min(min, other.min);
158 max = Math.max(max, other.max);
159 }
160
161 /**
162 * Returns the count of values recorded.
163 *
164 * @return the count of values
165 */
166 public final long getCount() {
167 return count;
168 }
169
170 /**
171 * Returns the sum of values recorded, or zero if no values have been
172 * recorded.
173 *
174 * @return the sum of values, or zero if none
175 */
176 public final long getSum() {
177 return sum;
178 }
179
180 /**
181 * Returns the minimum value recorded, or {@code Long.MAX_VALUE} if no
182 * values have been recorded.
183 *
184 * @return the minimum value, or {@code Long.MAX_VALUE} if none
185 */
186 public final long getMin() {
187 return min;
188 }
189
190 /**
191 * Returns the maximum value recorded, or {@code Long.MIN_VALUE} if no
192 * values have been recorded
193 *
194 * @return the maximum value, or {@code Long.MIN_VALUE} if none
195 */
196 public final long getMax() {
197 return max;
198 }
199
200 /**
201 * Returns the arithmetic mean of values recorded, or zero if no values have been
202 * recorded.
203 *
204 * @return The arithmetic mean of values, or zero if none
205 */
206 public final double getAverage() {
207 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d;
208 }
209
210 /**
211 * Returns a non-empty string representation of this object suitable for
212 * debugging. The exact presentation format is unspecified and may vary
213 * between implementations and versions.
214 */
215 @Override
216 public String toString() {
217 return String.format(
218 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}",
219 this.getClass().getSimpleName(),
220 getCount(),
221 getSum(),
222 getMin(),
223 getAverage(),
224 getMax());
225 }
226 }