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.math.stat.descriptive.summary;
18
19 import java.io.Serializable;
20
21 import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic;
22
23 /**
24 * Returns the product of the available values.
25 * <p>
26 * If there are no values in the dataset, or any of the values are
27 * <code>NaN</code>, then <code>NaN</code> is returned.</p>
28 * <p>
29 * <strong>Note that this implementation is not synchronized.</strong> If
30 * multiple threads access an instance of this class concurrently, and at least
31 * one of the threads invokes the <code>increment()</code> or
32 * <code>clear()</code> method, it must be synchronized externally.</p>
33 *
34 * @version $Revision: 762087 $ $Date: 2009-04-05 10:20:18 -0400 (Sun, 05 Apr 2009) $
35 */
36 public class Product extends AbstractStorelessUnivariateStatistic implements Serializable {
37
38 /** Serializable version identifier */
39 private static final long serialVersionUID = 2824226005990582538L;
40
41 /**The number of values that have been added */
42 private long n;
43
44 /**
45 * The current Running Product.
46 */
47 private double value;
48
49 /**
50 * Create a Product instance
51 */
52 public Product() {
53 n = 0;
54 value = Double.NaN;
55 }
56
57 /**
58 * Copy constructor, creates a new {@code Product} identical
59 * to the {@code original}
60 *
61 * @param original the {@code Product} instance to copy
62 */
63 public Product(Product original) {
64 copy(original, this);
65 }
66
67 /**
68 * {@inheritDoc}
69 */
70 @Override
71 public void increment(final double d) {
72 if (n == 0) {
73 value = d;
74 } else {
75 value *= d;
76 }
77 n++;
78 }
79
80 /**
81 * {@inheritDoc}
82 */
83 @Override
84 public double getResult() {
85 return value;
86 }
87
88 /**
89 * {@inheritDoc}
90 */
91 public long getN() {
92 return n;
93 }
94
95 /**
96 * {@inheritDoc}
97 */
98 @Override
99 public void clear() {
100 value = Double.NaN;
101 n = 0;
102 }
103
104 /**
105 * Returns the product of the entries in the specified portion of
106 * the input array, or <code>Double.NaN</code> if the designated subarray
107 * is empty.
108 * <p>
109 * Throws <code>IllegalArgumentException</code> if the array is null.</p>
110 *
111 * @param values the input array
112 * @param begin index of the first array element to include
113 * @param length the number of elements to include
114 * @return the product of the values or Double.NaN if length = 0
115 * @throws IllegalArgumentException if the array is null or the array index
116 * parameters are not valid
117 */
118 @Override
119 public double evaluate(final double[] values, final int begin, final int length) {
120 double product = Double.NaN;
121 if (test(values, begin, length)) {
122 product = 1.0;
123 for (int i = begin; i < begin + length; i++) {
124 product *= values[i];
125 }
126 }
127 return product;
128 }
129
130 /**
131 * {@inheritDoc}
132 */
133 @Override
134 public Product copy() {
135 Product result = new Product();
136 copy(this, result);
137 return result;
138 }
139
140 /**
141 * Copies source to dest.
142 * <p>Neither source nor dest can be null.</p>
143 *
144 * @param source Product to copy
145 * @param dest Product to copy to
146 * @throws NullPointerException if either source or dest is null
147 */
148 public static void copy(Product source, Product dest) {
149 dest.n = source.n;
150 dest.value = source.value;
151 }
152
153 }