01 /*
02 * Java Genetic Algorithm Library (jenetics-5.1.0).
03 * Copyright (c) 2007-2019 Franz Wilhelmstötter
04 *
05 * Licensed under the Apache License, Version 2.0 (the "License");
06 * you may not use this file except in compliance with the License.
07 * You may obtain a copy of the License at
08 *
09 * 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 * Author:
18 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
19 */
20 package io.jenetics.ext.util;
21
22 import static java.util.Objects.requireNonNull;
23
24 import java.util.Collections;
25 import java.util.Iterator;
26
27 /**
28 * Postorder iterator of the tree.
29 *
30 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
31 * @version 3.9
32 * @since 3.9
33 */
34 final class TreeNodePostorderIterator<V, T extends Tree<V, T>>
35 implements Iterator<T>
36 {
37
38 private T _root;
39 private final Iterator<T> _children;
40 private Iterator<T> _subtree;
41
42 /**
43 * Create a new postorder iterator of the given tree {@code root}.
44 *
45 * @param root the root node of the tree
46 * @throws NullPointerException if the given {@code root} node is
47 * {@code null}
48 */
49 TreeNodePostorderIterator(final T root) {
50 _root = requireNonNull(root);
51 _children = _root.childIterator();
52 _subtree = Collections.emptyIterator();
53 }
54
55 @Override
56 public boolean hasNext() {
57 return _root != null;
58 }
59
60 @Override
61 public T next() {
62 final T result;
63 if (_subtree.hasNext()) {
64 result = _subtree.next();
65 } else if (_children.hasNext()) {
66 _subtree = new TreeNodePostorderIterator<>(_children.next());
67 result = _subtree.next();
68 } else {
69 result = _root;
70 _root = null;
71 }
72
73 return result;
74 }
75
76 }
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