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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;
18  
19  import java.io.Serializable;
20  
21  /**
22   * Abstract base class for all implementations of the 
23   * {@link UnivariateStatistic} interface.
24   * <p>
25   * Provides a default implementation of <code>evaluate(double[]),</code> 
26   * delegating to <code>evaluate(double[], int, int)</code> in the natural way.
27   * </p>
28   * <p>
29   * Also includes a <code>test</code> method that performs generic parameter
30   * validation for the <code>evaluate</code> methods.</p>
31   * 
32   * @version $Revision: 617953 $ $Date: 2008-02-02 22:54:00 -0700 (Sat, 02 Feb 2008) $
33   */
34  public abstract class AbstractUnivariateStatistic
35      implements UnivariateStatistic, Serializable {
36      
37      /** Serialization UID */
38      private static final long serialVersionUID = -8007759382851708045L;
39  
40      /**
41       * @see org.apache.commons.math.stat.descriptive.UnivariateStatistic#evaluate(double[])
42       */
43      public double evaluate(final double[] values) {
44          test(values, 0, 0);
45          return evaluate(values, 0, values.length);
46      }
47  
48      /**
49       * @see org.apache.commons.math.stat.descriptive.UnivariateStatistic#evaluate(double[], int, int)
50       */
51      public abstract double evaluate(final double[] values, final int begin, final int length);
52  
53      /**
54       * This method is used by <code>evaluate(double[], int, int)</code> methods
55       * to verify that the input parameters designate a subarray of positive length.
56       * <p>
57       * <ul>
58       * <li>returns <code>true</code> iff the parameters designate a subarray of 
59       * positive length</li>
60       * <li>throws <code>IllegalArgumentException</code> if the array is null or
61       * or the indices are invalid</li>
62       * <li>returns <code>false</li> if the array is non-null, but 
63       * <code>length</code> is 0.
64       * </ul></p>
65       *
66       * @param values the input array
67       * @param begin index of the first array element to include
68       * @param length the number of elements to include
69       * @return true if the parameters are valid and designate a subarray of positive length
70       * @throws IllegalArgumentException if the indices are invalid or the array is null
71       */
72      protected boolean test(
73          final double[] values,
74          final int begin,
75          final int length) {
76  
77          if (values == null) {
78              throw new IllegalArgumentException("input value array is null");
79          }
80          
81          if (begin < 0) {
82              throw new IllegalArgumentException("start position cannot be negative");
83          }
84          
85          if (length < 0) {
86              throw new IllegalArgumentException("length cannot be negative");
87          }
88          
89          if (begin + length > values.length) {
90              throw new IllegalArgumentException(
91                  "begin + length > values.length");
92          }
93  
94          if (length == 0) {
95              return false;
96          }
97  
98          return true;
99  
100     }
101 }