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      @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    }