1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.eclipse.aether.util.graph.visitor;
20
21 import java.util.AbstractList;
22 import java.util.NoSuchElementException;
23 import java.util.RandomAccess;
24
25 /**
26 * A non-synchronized stack with a non-modifiable list view which starts at the top of the stack. While
27 * {@code LinkedList} can provide the same behavior, it creates many temp objects upon frequent pushes/pops.
28 */
29 class Stack<E> extends AbstractList<E> implements RandomAccess {
30
31 @SuppressWarnings("unchecked")
32 // CHECKSTYLE_OFF: MagicNumber
33 private E[] elements = (E[]) new Object[96];
34 // CHECKSTYLE_ON: MagicNumber
35
36 private int size;
37
38 public void push(E element) {
39 if (size >= elements.length) {
40 @SuppressWarnings("unchecked")
41 E[] tmp = (E[]) new Object[size + 64];
42 System.arraycopy(elements, 0, tmp, 0, elements.length);
43 elements = tmp;
44 }
45 elements[size++] = element;
46 }
47
48 public E pop() {
49 if (size <= 0) {
50 throw new NoSuchElementException();
51 }
52 return elements[--size];
53 }
54
55 public E peek() {
56 if (size <= 0) {
57 return null;
58 }
59 return elements[size - 1];
60 }
61
62 @Override
63 public E get(int index) {
64 if (index < 0 || index >= size) {
65 throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
66 }
67 return elements[size - index - 1];
68 }
69
70 @Override
71 public int size() {
72 return size;
73 }
74 }