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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      private E[] elements = (E[]) new Object[96];
33  
34      private int size;
35  
36      public void push(E element) {
37          if (size >= elements.length) {
38              @SuppressWarnings("unchecked")
39              E[] tmp = (E[]) new Object[size + 64];
40              System.arraycopy(elements, 0, tmp, 0, elements.length);
41              elements = tmp;
42          }
43          elements[size++] = element;
44      }
45  
46      public E pop() {
47          if (size <= 0) {
48              throw new NoSuchElementException();
49          }
50          return elements[--size];
51      }
52  
53      public E peek() {
54          if (size <= 0) {
55              return null;
56          }
57          return elements[size - 1];
58      }
59  
60      @Override
61      public E get(int index) {
62          if (index < 0 || index >= size) {
63              throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
64          }
65          return elements[size - index - 1];
66      }
67  
68      @Override
69      public int size() {
70          return size;
71      }
72  }