01 /*
02 * Java Genetic Algorithm Library (jenetics-2.0.2).
03 * Copyright (c) 2007-2014 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@gmx.at)
19 */
20 package org.jenetics.internal.util;
21
22 /**
23 * Minimal implementation of stack data-structure. {@code Null} values are not
24 * permitted, but not checked.
25 *
26 * [code]
27 * final Stack<Integer> stack = new Stack<>();
28 * for (int i = 0; i < 10; ++i) {
29 * stack.push(i);
30 * }
31 *
32 * for (Integer i = stack.pop(); i != null; i = stack.pop()) {
33 * System.out.println(i);
34 * }
35 * [/code]
36 *
37 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
38 * @version 2.0 — <em>$Date: 2014-03-28 $</em>
39 * @since 2.0
40 */
41 public final class Stack<T> {
42
43 private Node<T> _tail = null;
44
45 public int length = 0;
46
47 public void push(final T value) {
48 _tail = new Node<>(value, _tail);
49 ++length;
50 }
51
52 public T pop() {
53 T value = null;
54 if (_tail != null) {
55 value = _tail._value;
56 _tail = _tail._previous;
57 --length;
58 }
59
60 return value;
61 }
62
63
64 private static final class Node<T> {
65 final T _value;
66 final Node<T> _previous;
67
68 Node(final T value, final Node<T> previous) {
69 _value = value;
70 _previous = previous;
71 }
72 }
73 }
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