001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.commons.collections; 018 019 import java.util.ArrayList; 020 import java.util.EmptyStackException; 021 022 /** 023 * An implementation of the {@link java.util.Stack} API that is based on an 024 * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not 025 * synchronized to protect against multi-threaded access. The implementation 026 * is therefore operates faster in environments where you do not need to 027 * worry about multiple thread contention. 028 * <p> 029 * The removal order of an <code>ArrayStack</code> is based on insertion 030 * order: The most recently added element is removed first. The iteration 031 * order is <i>not</i> the same as the removal order. The iterator returns 032 * elements from the bottom up, whereas the {@link #remove()} method removes 033 * them from the top down. 034 * <p> 035 * Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries. 036 * 037 * @see java.util.Stack 038 * @since Commons Collections 1.0 039 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $ 040 * 041 * @author Craig R. McClanahan 042 * @author Paul Jack 043 * @author Stephen Colebourne 044 */ 045 public class ArrayStack extends ArrayList implements Buffer { 046 047 /** Ensure serialization compatibility */ 048 private static final long serialVersionUID = 2130079159931574599L; 049 050 /** 051 * Constructs a new empty <code>ArrayStack</code>. The initial size 052 * is controlled by <code>ArrayList</code> and is currently 10. 053 */ 054 public ArrayStack() { 055 super(); 056 } 057 058 /** 059 * Constructs a new empty <code>ArrayStack</code> with an initial size. 060 * 061 * @param initialSize the initial size to use 062 * @throws IllegalArgumentException if the specified initial size 063 * is negative 064 */ 065 public ArrayStack(int initialSize) { 066 super(initialSize); 067 } 068 069 /** 070 * Return <code>true</code> if this stack is currently empty. 071 * <p> 072 * This method exists for compatibility with <code>java.util.Stack</code>. 073 * New users of this class should use <code>isEmpty</code> instead. 074 * 075 * @return true if the stack is currently empty 076 */ 077 public boolean empty() { 078 return isEmpty(); 079 } 080 081 /** 082 * Returns the top item off of this stack without removing it. 083 * 084 * @return the top item on the stack 085 * @throws EmptyStackException if the stack is empty 086 */ 087 public Object peek() throws EmptyStackException { 088 int n = size(); 089 if (n <= 0) { 090 throw new EmptyStackException(); 091 } else { 092 return get(n - 1); 093 } 094 } 095 096 /** 097 * Returns the n'th item down (zero-relative) from the top of this 098 * stack without removing it. 099 * 100 * @param n the number of items down to go 101 * @return the n'th item on the stack, zero relative 102 * @throws EmptyStackException if there are not enough items on the 103 * stack to satisfy this request 104 */ 105 public Object peek(int n) throws EmptyStackException { 106 int m = (size() - n) - 1; 107 if (m < 0) { 108 throw new EmptyStackException(); 109 } else { 110 return get(m); 111 } 112 } 113 114 /** 115 * Pops the top item off of this stack and return it. 116 * 117 * @return the top item on the stack 118 * @throws EmptyStackException if the stack is empty 119 */ 120 public Object pop() throws EmptyStackException { 121 int n = size(); 122 if (n <= 0) { 123 throw new EmptyStackException(); 124 } else { 125 return remove(n - 1); 126 } 127 } 128 129 /** 130 * Pushes a new item onto the top of this stack. The pushed item is also 131 * returned. This is equivalent to calling <code>add</code>. 132 * 133 * @param item the item to be added 134 * @return the item just pushed 135 */ 136 public Object push(Object item) { 137 add(item); 138 return item; 139 } 140 141 /** 142 * Returns the one-based position of the distance from the top that the 143 * specified object exists on this stack, where the top-most element is 144 * considered to be at distance <code>1</code>. If the object is not 145 * present on the stack, return <code>-1</code> instead. The 146 * <code>equals()</code> method is used to compare to the items 147 * in this stack. 148 * 149 * @param object the object to be searched for 150 * @return the 1-based depth into the stack of the object, or -1 if not found 151 */ 152 public int search(Object object) { 153 int i = size() - 1; // Current index 154 int n = 1; // Current distance 155 while (i >= 0) { 156 Object current = get(i); 157 if ((object == null && current == null) || 158 (object != null && object.equals(current))) { 159 return n; 160 } 161 i--; 162 n++; 163 } 164 return -1; 165 } 166 167 /** 168 * Returns the element on the top of the stack. 169 * 170 * @return the element on the top of the stack 171 * @throws BufferUnderflowException if the stack is empty 172 */ 173 public Object get() { 174 int size = size(); 175 if (size == 0) { 176 throw new BufferUnderflowException(); 177 } 178 return get(size - 1); 179 } 180 181 /** 182 * Removes the element on the top of the stack. 183 * 184 * @return the removed element 185 * @throws BufferUnderflowException if the stack is empty 186 */ 187 public Object remove() { 188 int size = size(); 189 if (size == 0) { 190 throw new BufferUnderflowException(); 191 } 192 return remove(size - 1); 193 } 194 195 }