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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  
18  package org.apache.commons.math.complex;
19  
20  import java.io.Serializable;
21  
22  import org.apache.commons.math.Field;
23  
24  /**
25   * Representation of the complex numbers field.
26   * <p>
27   * This class is a singleton.
28   * </p>
29   * @see Complex
30   * @version $Revision: 795911 $ $Date: 2009-07-20 12:48:30 -0400 (Mon, 20 Jul 2009) $
31   * @since 2.0
32   */
33  public class ComplexField implements Field<Complex>, Serializable  {
34  
35      /** Serializable version identifier. */
36      private static final long serialVersionUID = -6130362688700788798L;
37  
38      /** Private constructor for the singleton.
39       */
40      private ComplexField() {
41      }
42  
43      /** Get the unique instance.
44       * @return the unique instance
45       */
46      public static ComplexField getInstance() {
47          return LazyHolder.INSTANCE;
48      }
49  
50      /** {@inheritDoc} */
51      public Complex getOne() {
52          return Complex.ONE;
53      }
54  
55      /** {@inheritDoc} */
56      public Complex getZero() {
57          return Complex.ZERO;
58      }
59  
60      /** Holder for the instance.
61       * <p>We use here the Initialization On Demand Holder Idiom.</p>
62       */
63      private static class LazyHolder {
64          /** Cached field instance. */
65          private static final ComplexField INSTANCE = new ComplexField();
66      }
67  
68      /** Handle deserialization of the singleton.
69       * @return the singleton instance
70       */
71      private Object readResolve() {
72          // return the singleton instance
73          return LazyHolder.INSTANCE; 
74      }
75  
76  }