1 /*
2 * Copyright 2004-2009 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
17 package org.springmodules.validation.util.collection;
18
19 import java.util.Iterator;
20 import java.util.NoSuchElementException;
21
22 import org.springmodules.validation.util.condition.Condition;
23
24 /**
25 * An wrapper iterator that filters out items from the underlying iterator based on a condition.
26 *
27 * @author Uri Boness
28 */
29 public class FilteredIterator extends ReadOnlyIterator {
30
31 private Condition condition;
32
33 private Iterator iterator;
34
35 private boolean initialized;
36
37 private boolean finished;
38
39 private Object nextElement;
40
41 /**
42 * Constructs a new FilteredIterator with given iterator to wrap and a condition. The constructed iterator will
43 * return only the element that adhere to the given condition.
44 *
45 * @param iterator The iterator to wrap.
46 * @param condition The condition that determines what elements should be returned by this iterator.
47 */
48 public FilteredIterator(Iterator iterator, Condition condition) {
49 this.iterator = iterator;
50 this.condition = condition;
51 }
52
53 public boolean hasNext() {
54 initializeIfNeeded();
55 return !finished;
56 }
57
58 public Object next() {
59 if (!hasNext()) {
60 throw new NoSuchElementException();
61 }
62 Object result = nextElement;
63 advanceIterator();
64 return result;
65 }
66
67 //=============================================== Helper Methods ===================================================
68
69 protected void initializeIfNeeded() {
70 if (!initialized) {
71 advanceIterator();
72 initialized = true;
73 }
74 }
75
76 protected void advanceIterator() {
77 boolean assigned = false;
78 while (iterator.hasNext()) {
79 Object element = iterator.next();
80 if (condition.check(element)) {
81 nextElement = element;
82 assigned = true;
83 break;
84 }
85 }
86 finished = !assigned;
87 }
88
89 }