PredicateTransformer


1   /*
2    *  Copyright 2001-2004 The Apache Software Foundation
3    *
4    *  Licensed under the Apache License, Version 2.0 (the "License");
5    *  you may not use this file except in compliance with the License.
6    *  You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   *  Unless required by applicable law or agreed to in writing, software
11   *  distributed under the License is distributed on an "AS IS" BASIS,
12   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   *  See the License for the specific language governing permissions and
14   *  limitations under the License.
15   */
16  package org.apache.commons.collections.functors;
17  
18  import java.io.Serializable  ;
19  
20  import org.apache.commons.collections.Predicate;
21  import org.apache.commons.collections.Transformer;
22  
23  /**
24   * Transformer implementation that calls a Predicate using the input object
25   * and then returns the input.
26   * 
27   * @since Commons Collections 3.0
28   * @version $Revision: 1.5 $ $Date: 2004/05/16 11:36:31 $
29   *
30   * @author Stephen Colebourne
31   */
32  public class PredicateTransformer implements Transformer, Serializable   {
33  
34      /** Serial version UID */
35      static final long serialVersionUID = 5278818408044349346L;
36  
37      /** The closure to wrap */
38      private final Predicate iPredicate;
39  
40      /**
41       * Factory method that performs validation.
42       * 
43       * @param predicate  the predicate to call, not null
44       * @return the <code>predicate</code> transformer
45       * @throws IllegalArgumentException if the predicate is null
46       */
47      public static Transformer getInstance(Predicate predicate) {
48          if (predicate == null) {
49              throw new IllegalArgumentException  ("Predicate must not be null");
50          }
51          return new PredicateTransformer(predicate);
52      }
53  
54      /**
55       * Constructor that performs no validation.
56       * Use <code>getInstance</code> if you want that.
57       * 
58       * @param predicate  the predicate to call, not null
59       */
60      public PredicateTransformer(Predicate predicate) {
61          super();
62          iPredicate = predicate;
63      }
64  
65      /**
66       * Transforms the input to result by calling a predicate.
67       * 
68       * @param input  the input object to transform
69       * @return the transformed result
70       */
71      public Object   transform(Object   input) {
72          return (iPredicate.evaluate(input) ? Boolean.TRUE : Boolean.FALSE);
73      }
74  
75      /**
76       * Gets the predicate.
77       * 
78       * @return the predicate
79       * @since Commons Collections 3.1
80       */
81      public Predicate getPredicate() {
82          return iPredicate;
83      }
84  
85  }
86
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