1   /* Copyright 2013-2019 CS Systèmes d'Information
2    * Licensed to CS Systèmes d'Information (CS) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * CS 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.orekit.rugged.utils;
18  
19  /** Selector for min value.
20   * <p>
21   * This selector considers {@code Double.NaN} values correspond
22   * to non-initialized data that should be ignored rather than
23   * selected.
24   * </p>
25   * @see MaxSelector
26   * @author Luc Maisonobe
27   */
28  public class MinSelector extends Selector {
29  
30      /** Private constructor for singleton.
31       */
32      private MinSelector() {
33      }
34  
35      /** Get the unique instance.
36       * @return unique instance of the min selector.
37       */
38      public static MinSelector getInstance() {
39          return LazyHolder.INSTANCE;
40      }
41  
42      /** Check if first value should be selected.
43       * @param v1 first value
44       * @param v2 second value
45       * @return true if v1 is lower than v2, or if v2 is {@code Double.NaN}
46       */
47      @Override
48      public boolean selectFirst(final double v1, final double v2) {
49          return v1 < v2 || Double.isNaN(v2);
50      }
51  
52      /** Holder for the min selector singleton.
53       * <p>
54       * We use the Initialization On Demand Holder Idiom to store
55       * the singletons, as it is both thread-safe, efficient (no
56       * synchronization) and works with all versions of java.
57       * </p>
58       */
59      private static class LazyHolder {
60  
61          /** Unique instance. */
62          private static final MinSelector.html#MinSelector">MinSelector INSTANCE = new MinSelector();
63  
64          /** Private constructor.
65           * <p>This class is a utility class, it should neither have a public
66           * nor a default constructor. This private constructor prevents
67           * the compiler from generating one automatically.</p>
68           */
69          private LazyHolder() {
70          }
71  
72      }
73  
74  }