1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.statistics.descriptive;
18
19 /**
20 * Returns the maximum of the available values. Uses {@link Math#max(double, double) Math.max} as an
21 * underlying function to compute the {@code maximum}.
22 *
23 * <ul>
24 * <li>The result is {@link Double#NEGATIVE_INFINITY negative infinity} if no values are added.
25 * <li>The result is {@code NaN} if any of the values is {@code NaN}.
26 * <li>The value {@code -0.0} is considered strictly smaller than {@code 0.0}.
27 * </ul>
28 *
29 * <p>This class is designed to work with (though does not require)
30 * {@linkplain java.util.stream streams}.
31 *
32 * <p><strong>This implementation is not thread safe.</strong>
33 * If multiple threads access an instance of this class concurrently,
34 * and at least one of the threads invokes the {@link java.util.function.DoubleConsumer#accept(double) accept} or
35 * {@link StatisticAccumulator#combine(StatisticResult) combine} method, it must be synchronized externally.
36 *
37 * <p>However, it is safe to use {@link java.util.function.DoubleConsumer#accept(double) accept}
38 * and {@link StatisticAccumulator#combine(StatisticResult) combine}
39 * as {@code accumulator} and {@code combiner} functions of
40 * {@link java.util.stream.Collector Collector} on a parallel stream,
41 * because the parallel implementation of {@link java.util.stream.Stream#collect Stream.collect()}
42 * provides the necessary partitioning, isolation, and merging of results for
43 * safe and efficient parallel execution.
44 *
45 * @since 1.1
46 * @see Math#max(double, double)
47 */
48 public final class Max implements DoubleStatistic, StatisticAccumulator<Max> {
49
50 /** Current maximum. */
51 private double maximum = Double.NEGATIVE_INFINITY;
52
53 /**
54 * Create an instance.
55 */
56 private Max() {
57 // No-op
58 }
59
60 /**
61 * Creates an instance.
62 *
63 * <p>The initial result is {@link Double#NEGATIVE_INFINITY negative infinity}.
64 *
65 * @return {@code Max} instance.
66 */
67 public static Max create() {
68 return new Max();
69 }
70
71 /**
72 * Returns an instance populated using the input {@code values}.
73 *
74 * <p>The result is {@code NaN} if any of the values is {@code NaN}.
75 *
76 * <p>When the input is an empty array, the result is
77 * {@link Double#NEGATIVE_INFINITY negative infinity}.
78 *
79 * @param values Values.
80 * @return {@code Max} instance.
81 */
82 public static Max of(double... values) {
83 return Statistics.add(new Max(), values);
84 }
85
86 /**
87 * Updates the state of the statistic to reflect the addition of {@code value}.
88 *
89 * @param value Value.
90 */
91 @Override
92 public void accept(double value) {
93 maximum = Math.max(maximum, value);
94 }
95
96 /**
97 * Gets the maximum of all input values.
98 *
99 * <p>When no values have been added, the result is
100 * {@link Double#NEGATIVE_INFINITY negative infinity}.
101 *
102 * @return maximum of all values.
103 */
104 @Override
105 public double getAsDouble() {
106 return maximum;
107 }
108
109 @Override
110 public Max combine(Max other) {
111 accept(other.getAsDouble());
112 return this;
113 }
114 }