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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 }