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
006This file is part of GNU Classpath.
007
008GNU Classpath is free software; you can redistribute it and/or modify
009it under the terms of the GNU General Public License as published by
010the Free Software Foundation; either version 2, or (at your option)
011any later version.
012
013GNU Classpath is distributed in the hope that it will be useful, but
014WITHOUT ANY WARRANTY; without even the implied warranty of
015MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
016General Public License for more details.
017
018You should have received a copy of the GNU General Public License
019along with GNU Classpath; see the file COPYING.  If not, write to the
020Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02102110-1301 USA.
022
023Linking this library statically or dynamically with other modules is
024making a combined work based on this library.  Thus, the terms and
025conditions of the GNU General Public License cover the whole
026combination.
027
028As a special exception, the copyright holders of this library give you
029permission to link this library with independent modules to produce an
030executable, regardless of the license terms of these independent
031modules, and to copy and distribute the resulting executable under
032terms of your choice, provided that you also meet, for each linked
033independent module, the terms and conditions of the license of that
034module.  An independent module is a module which is not derived from
035or based on this library.  If you modify this library, you may extend
036this exception to your version of the library, but you are not
037obligated to do so.  If you do not wish to do so, delete this
038exception statement from your version. */
039
040
041package 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 */
062public 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  @SuppressWarnings("unchecked")
106  public synchronized T pop()
107  {
108    if (elementCount == 0)
109      throw new EmptyStackException();
110
111    modCount++;
112    T obj = (T) elementData[--elementCount];
113
114    // Set topmost element to null to assist the gc in cleanup.
115    elementData[elementCount] = null;
116    return obj;
117  }
118
119  /**
120   * Returns the top Object on the stack without removing it.
121   *
122   * @return the top Object on the stack
123   * @throws EmptyStackException if the stack is empty
124   */
125  @SuppressWarnings("unchecked")
126  public synchronized T peek()
127  {
128    if (elementCount == 0)
129      throw new EmptyStackException();
130
131    return (T) elementData[elementCount - 1];
132  }
133
134  /**
135   * Tests if the stack is empty.
136   *
137   * @return true if the stack contains no items, false otherwise
138   */
139  public synchronized boolean empty()
140  {
141    return elementCount == 0;
142  }
143
144  /**
145   * Returns the position of an Object on the stack, with the top
146   * most Object being at position 1, and each Object deeper in the
147   * stack at depth + 1.
148   *
149   * @param o The object to search for
150   * @return The 1 based depth of the Object, or -1 if the Object
151   *         is not on the stack
152   */
153  public synchronized int search(Object o)
154  {
155    int i = elementCount;
156    while (--i >= 0)
157      if (equals(o, elementData[i]))
158        return elementCount - i;
159    return -1;
160  }
161}