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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.rank;
18  
19  import java.io.Serializable;
20  
21  import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic;
22  
23  /**
24   * Returns the maximum of the available values.
25   * <p>
26   * <ul>
27   * <li>The result is <code>NaN</code> iff all values are <code>NaN</code> 
28   * (i.e. <code>NaN</code> values have no impact on the value of the statistic).</li>
29   * <li>If any of the values equals <code>Double.POSITIVE_INFINITY</code>, 
30   * the result is <code>Double.POSITIVE_INFINITY.</code></li>
31   * </ul></p>
32  * <p>
33   * <strong>Note that this implementation is not synchronized.</strong> If 
34   * multiple threads access an instance of this class concurrently, and at least
35   * one of the threads invokes the <code>increment()</code> or 
36   * <code>clear()</code> method, it must be synchronized externally.</p>
37   * 
38   * @version $Revision: 780541 $ $Date: 2009-05-31 20:47:02 -0400 (Sun, 31 May 2009) $
39   */
40  public class Max extends AbstractStorelessUnivariateStatistic implements Serializable {
41  
42      /** Serializable version identifier */
43      private static final long serialVersionUID = -5593383832225844641L;    
44      
45      /** Number of values that have been added */
46      private long n;
47          
48      /** Current value of the statistic */
49      private double value;
50  
51      /**
52       * Create a Max instance
53       */
54      public Max() {
55          n = 0;
56          value = Double.NaN;
57      }
58      
59      /**
60       * Copy constructor, creates a new {@code Max} identical
61       * to the {@code original}
62       * 
63       * @param original the {@code Max} instance to copy
64       */
65      public Max(Max original) {
66          copy(original, this);
67      }
68      
69      /**
70       * {@inheritDoc}
71       */
72      @Override
73      public void increment(final double d) {
74          if (d > value || Double.isNaN(value)) {
75              value = d;
76          }
77          n++;
78      }
79  
80      /**
81       * {@inheritDoc}
82       */
83      @Override
84      public void clear() {
85          value = Double.NaN;
86          n = 0;
87      }
88  
89      /**
90       * {@inheritDoc}
91       */
92      @Override
93      public double getResult() {
94          return value;
95      }
96  
97      /**
98       * {@inheritDoc}
99       */
100     public long getN() {
101         return n;
102     }
103     
104     /**
105      * Returns the maximum 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 or
110      * the array index parameters are not valid.</p>
111      * <p>
112      * <ul>
113      * <li>The result is <code>NaN</code> iff all values are <code>NaN</code> 
114      * (i.e. <code>NaN</code> values have no impact on the value of the statistic).</li>
115      * <li>If any of the values equals <code>Double.POSITIVE_INFINITY</code>, 
116      * the result is <code>Double.POSITIVE_INFINITY.</code></li>
117      * </ul></p>
118      * 
119      * @param values the input array
120      * @param begin index of the first array element to include
121      * @param length the number of elements to include
122      * @return the maximum of the values or Double.NaN if length = 0
123      * @throws IllegalArgumentException if the array is null or the array index
124      *  parameters are not valid
125      */
126     @Override
127     public double evaluate(final double[] values, final int begin, final int length) {
128         double max = Double.NaN;
129         if (test(values, begin, length)) {
130             max = values[begin];
131             for (int i = begin; i < begin + length; i++) {
132                 if (!Double.isNaN(values[i])) {
133                     max = (max > values[i]) ? max : values[i];
134                 }
135             }
136         }
137         return max;
138     }
139     
140     /**
141      * {@inheritDoc}
142      */
143     @Override
144     public Max copy() {
145         Max result = new Max();
146         copy(this, result);
147         return result;
148     }
149     
150     /**
151      * Copies source to dest.
152      * <p>Neither source nor dest can be null.</p>
153      * 
154      * @param source Max to copy
155      * @param dest Max to copy to
156      * @throws NullPointerException if either source or dest is null
157      */
158     public static void copy(Max source, Max dest) {
159         dest.n = source.n;
160         dest.value = source.value;
161     }
162 }