CompositeIterator


1   /*
2    * Copyright 2002-2006 the original author or authors.
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.springframework.binding.collection;
17  
18  import java.util.Iterator  ;
19  import java.util.LinkedList  ;
20  import java.util.List  ;
21  import java.util.NoSuchElementException  ;
22  
23  import org.springframework.util.Assert;
24  
25  /**
26   * Iterator that combines multiple other iterators. This is a simple implementation
27   * that just maintains a list of iterators which are invoked in sequence untill
28   * all iterators are exhausted.
29   * 
30   * @author Erwin Vervaet
31   */
32  public class CompositeIterator implements Iterator   {
33  
34      private List   iterators = new LinkedList  ();
35      
36      private boolean inUse = false;
37  
38      /**
39       * Create a new composite iterator. Add iterators using the {@link #add(Iterator)} method.
40       */
41      public CompositeIterator() {
42      }
43      
44      /**
45       * Add given iterator to this composite.
46       */
47      public void add(Iterator   iterator) {
48          Assert.state(!inUse, "You can no longer add iterator to a composite iterator that's already in use");
49          if (iterators.contains(iterator)) {
50              throw new IllegalArgumentException  ("You cannot add the same iterator twice");
51          }
52          iterators.add(iterator);
53      }
54  
55      public boolean hasNext() {
56          inUse = true;
57          for (Iterator   it = iterators.iterator(); it.hasNext(); ) {
58              if (((Iterator  )it.next()).hasNext()) {
59                  return true;
60              }
61          }
62          return false;
63      }
64  
65      public Object   next() {
66          inUse = true;
67          for (Iterator   it = iterators.iterator(); it.hasNext(); ) {
68              Iterator   iterator = (Iterator  )it.next();
69              if (iterator.hasNext()) {
70                  return iterator.next();
71              }
72          }
73          throw new NoSuchElementException  ("Exhaused all iterators");
74      }
75  
76      public void remove() {
77          throw new UnsupportedOperationException  ("Remove is not supported");
78      }       
79  }
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