TransformIterator


1   /*
2    *  Copyright 1999-2004 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.iterators;
17  
18  import java.util.Iterator  ;
19  
20  import org.apache.commons.collections.Transformer;
21  
22  /** 
23   * Decorates an iterator such that each element returned is transformed.
24   *
25   * @since Commons Collections 1.0
26   * @version $Revision: 1.9 $ $Date: 2004/02/18 00:59:50 $
27   * 
28   * @author James Strachan
29   * @author Stephen Colebourne
30   */
31  public class TransformIterator implements Iterator   {
32  
33      /** The iterator being used */
34      private Iterator   iterator;
35      /** The transformer being used */
36      private Transformer transformer;
37  
38      //-----------------------------------------------------------------------
39      /**
40       * Constructs a new <code>TransformIterator</code> that will not function
41       * until the {@link #setIterator(Iterator) setIterator} method is 
42       * invoked.
43       */
44      public TransformIterator() {
45          super();
46      }
47  
48      /**
49       * Constructs a new <code>TransformIterator</code> that won't transform
50       * elements from the given iterator.
51       *
52       * @param iterator  the iterator to use
53       */
54      public TransformIterator(Iterator   iterator) {
55          super();
56          this.iterator = iterator;
57      }
58  
59      /**
60       * Constructs a new <code>TransformIterator</code> that will use the
61       * given iterator and transformer.  If the given transformer is null,
62       * then objects will not be transformed.
63       *
64       * @param iterator  the iterator to use
65       * @param transformer  the transformer to use
66       */
67      public TransformIterator(Iterator   iterator, Transformer transformer) {
68          super();
69          this.iterator = iterator;
70          this.transformer = transformer;
71      }
72  
73      //-----------------------------------------------------------------------
74      public boolean hasNext() {
75          return iterator.hasNext();
76      }
77  
78      /**
79       * Gets the next object from the iteration, transforming it using the
80       * current transformer. If the transformer is null, no transformation
81       * occurs and the object from the iterator is returned directly.
82       * 
83       * @return the next object
84       * @throws java.util.NoSuchElementException if there are no more elements
85       */
86      public Object   next() {
87          return transform(iterator.next());
88      }
89  
90      public void remove() {
91          iterator.remove();
92      }
93  
94      //-----------------------------------------------------------------------
95      /** 
96       * Gets the iterator this iterator is using.
97       * 
98       * @return the iterator.
99       */
100     public Iterator   getIterator() {
101         return iterator;
102     }
103 
104     /** 
105      * Sets the iterator for this iterator to use.
106      * If iteration has started, this effectively resets the iterator.
107      * 
108      * @param iterator  the iterator to use
109      */
110     public void setIterator(Iterator   iterator) {
111         this.iterator = iterator;
112     }
113 
114     //-----------------------------------------------------------------------
115     /** 
116      * Gets the transformer this iterator is using.
117      * 
118      * @return the transformer.
119      */
120     public Transformer getTransformer() {
121         return transformer;
122     }
123 
124     /** 
125      * Sets the transformer this the iterator to use.
126      * A null transformer is a no-op transformer.
127      * 
128      * @param transformer  the transformer to use
129      */
130     public void setTransformer(Transformer transformer) {
131         this.transformer = transformer;
132     }
133 
134     //-----------------------------------------------------------------------
135     /**
136      * Transforms the given object using the transformer.
137      * If the transformer is null, the original object is returned as-is.
138      *
139      * @param source  the object to transform
140      * @return the transformed object
141      */
142     protected Object   transform(Object   source) {
143         if (transformer != null) {
144             return transformer.transform(source);
145         }
146         return source;
147     }
148 }
149
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