001 /* Stack.java - Class that provides a Last In First Out (LIFO)
002 datatype, known more commonly as a Stack
003 Copyright (C) 1998, 1999, 2001, 2004, 2005
004 Free Software Foundation, Inc.
005
006 This file is part of GNU Classpath.
007
008 GNU Classpath is free software; you can redistribute it and/or modify
009 it under the terms of the GNU General Public License as published by
010 the Free Software Foundation; either version 2, or (at your option)
011 any later version.
012
013 GNU Classpath is distributed in the hope that it will be useful, but
014 WITHOUT ANY WARRANTY; without even the implied warranty of
015 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
016 General Public License for more details.
017
018 You should have received a copy of the GNU General Public License
019 along with GNU Classpath; see the file COPYING. If not, write to the
020 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
021 02110-1301 USA.
022
023 Linking this library statically or dynamically with other modules is
024 making a combined work based on this library. Thus, the terms and
025 conditions of the GNU General Public License cover the whole
026 combination.
027
028 As a special exception, the copyright holders of this library give you
029 permission to link this library with independent modules to produce an
030 executable, regardless of the license terms of these independent
031 modules, and to copy and distribute the resulting executable under
032 terms of your choice, provided that you also meet, for each linked
033 independent module, the terms and conditions of the license of that
034 module. An independent module is a module which is not derived from
035 or based on this library. If you modify this library, you may extend
036 this exception to your version of the library, but you are not
037 obligated to do so. If you do not wish to do so, delete this
038 exception statement from your version. */
039
040
041 package java.util;
042
043 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
044 * "The Java Language Specification", ISBN 0-201-63451-1
045 * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
046 * Status: Believed complete and correct
047
048 /**
049 * Stack provides a Last In First Out (LIFO) data type, commonly known
050 * as a Stack. Stack itself extends Vector and provides the additional
051 * methods for stack manipulation (push, pop, peek). You can also seek for
052 * the 1-based position of an element on the stack.
053 *
054 * @author Warren Levy (warrenl@cygnus.com)
055 * @author Eric Blake (ebb9@email.byu.edu)
056 * @see List
057 * @see AbstractList
058 * @see LinkedList
059 * @since 1.0
060 * @status updated to 1.4
061 */
062 public class Stack<T> extends Vector<T>
063 {
064 // We could use Vector methods internally for the following methods,
065 // but have used Vector fields directly for efficiency (i.e. this
066 // often reduces out duplicate bounds checking).
067
068 /**
069 * Compatible with JDK 1.0+.
070 */
071 private static final long serialVersionUID = 1224463164541339165L;
072
073 /**
074 * This constructor creates a new Stack, initially empty
075 */
076 public Stack()
077 {
078 }
079
080 /**
081 * Pushes an Object onto the top of the stack. This method is effectively
082 * the same as addElement(item).
083 *
084 * @param item the Object to push onto the stack
085 * @return the Object pushed onto the stack
086 * @see Vector#addElement(Object)
087 */
088 public T push(T item)
089 {
090 // When growing the Stack, use the Vector routines in case more
091 // memory is needed.
092 // Note: spec indicates that this method *always* returns obj passed in!
093
094 addElement(item);
095 return item;
096 }
097
098 /**
099 * Pops an item from the stack and returns it. The item popped is
100 * removed from the Stack.
101 *
102 * @return the Object popped from the stack
103 * @throws EmptyStackException if the stack is empty
104 */
105 public synchronized T pop()
106 {
107 if (elementCount == 0)
108 throw new EmptyStackException();
109
110 modCount++;
111 T obj = elementData[--elementCount];
112
113 // Set topmost element to null to assist the gc in cleanup.
114 elementData[elementCount] = null;
115 return obj;
116 }
117
118 /**
119 * Returns the top Object on the stack without removing it.
120 *
121 * @return the top Object on the stack
122 * @throws EmptyStackException if the stack is empty
123 */
124 public synchronized T peek()
125 {
126 if (elementCount == 0)
127 throw new EmptyStackException();
128
129 return elementData[elementCount - 1];
130 }
131
132 /**
133 * Tests if the stack is empty.
134 *
135 * @return true if the stack contains no items, false otherwise
136 */
137 public synchronized boolean empty()
138 {
139 return elementCount == 0;
140 }
141
142 /**
143 * Returns the position of an Object on the stack, with the top
144 * most Object being at position 1, and each Object deeper in the
145 * stack at depth + 1.
146 *
147 * @param o The object to search for
148 * @return The 1 based depth of the Object, or -1 if the Object
149 * is not on the stack
150 */
151 public synchronized int search(Object o)
152 {
153 int i = elementCount;
154 while (--i >= 0)
155 if (equals(o, elementData[i]))
156 return elementCount - i;
157 return -1;
158 }
159 }