libjava/java/util/Stack.java

   1 /* Stack.java - Class that provides a Last In First Out (LIFO)
   2    datatype, known more commonly as a Stack
   3    Copyright (C) 1998, 1999, 2001 Free Software Foundation, Inc.
   4
   5 This file is part of GNU Classpath.
   6
   7 GNU Classpath is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GNU Classpath is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Classpath; see the file COPYING.  If not, write to the
  19 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20 02111-1307 USA.
  21
  22 Linking this library statically or dynamically with other modules is
  23 making a combined work based on this library.  Thus, the terms and
  24 conditions of the GNU General Public License cover the whole
  25 combination.
  26
  27 As a special exception, the copyright holders of this library give you
  28 permission to link this library with independent modules to produce an
  29 executable, regardless of the license terms of these independent
  30 modules, and to copy and distribute the resulting executable under
  31 terms of your choice, provided that you also meet, for each linked
  32 independent module, the terms and conditions of the license of that
  33 module.  An independent module is a module which is not derived from
  34 or based on this library.  If you modify this library, you may extend
  35 this exception to your version of the library, but you are not
  36 obligated to do so.  If you do not wish to do so, delete this
  37 exception statement from your version. */
  38
  39
  40 package java.util;
  41
  42 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  43  * "The Java Language Specification", ISBN 0-201-63451-1
  44  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
  45  * Status:  Believed complete and correct
  46
  47 /**
  48  * Stack provides a Last In First Out (LIFO) data type, commonly known
  49  * as a Stack.  Stack itself extends Vector and provides the additional
  50  * methods for stack manipulation (push, pop, peek). You can also seek for
  51  * the 1-based position of an element on the stack.
  52  *
  53  * @author Warren Levy <warrenl@cygnus.com>
  54  * @author Eric Blake <ebb9@email.byu.edu>
  55  * @see List
  56  * @see AbstractList
  57  * @see LinkedList
  58  * @since 1.0
  59  * @status updated to 1.4
  60  */
  61 public class Stack extends Vector
  62 {
  63   // We could use Vector methods internally for the following methods,
  64   // but have used Vector fields directly for efficiency (i.e. this
  65   // often reduces out duplicate bounds checking).
  66
  67   /**
  68    * Compatible with JDK 1.0+.
  69    */
  70   private static final long serialVersionUID = 1224463164541339165L;
  71
  72   /**
  73    * This constructor creates a new Stack, initially empty
  74    */
  75   public Stack()
  76   {
  77   }
  78
  79   /**
  80    * Pushes an Object onto the top of the stack.  This method is effectively
  81    * the same as addElement(item).
  82    *
  83    * @param item the Object to push onto the stack
  84    * @return the Object pushed onto the stack
  85    * @see Vector#addElement(Object)
  86    */
  87   public Object push(Object item)
  88   {
  89     // When growing the Stack, use the Vector routines in case more
  90     // memory is needed.
  91     // Note: spec indicates that this method *always* returns obj passed in!
  92
  93     addElement(item);
  94     return item;
  95   }
  96
  97   /**
  98    * Pops an item from the stack and returns it.  The item popped is
  99    * removed from the Stack.
 100    *
 101    * @return the Object popped from the stack
 102    * @throws EmptyStackException if the stack is empty
 103    */
 104   public synchronized Object pop()
 105   {
 106     if (elementCount == 0)
 107       throw new EmptyStackException();
 108
 109     modCount++;
 110     Object obj = elementData[--elementCount];
 111
 112     // Set topmost element to null to assist the gc in cleanup.
 113     elementData[elementCount] = null;
 114     return obj;
 115   }
 116
 117   /**
 118    * Returns the top Object on the stack without removing it.
 119    *
 120    * @return the top Object on the stack
 121    * @throws EmptyStackException if the stack is empty
 122    */
 123   public synchronized Object peek()
 124   {
 125     if (elementCount == 0)
 126       throw new EmptyStackException();
 127
 128     return elementData[elementCount - 1];
 129   }
 130
 131   /**
 132    * Tests if the stack is empty.
 133    *
 134    * @return true if the stack contains no items, false otherwise
 135    */
 136   public synchronized boolean empty()
 137   {
 138     return elementCount == 0;
 139   }
 140
 141   /**
 142    * Returns the position of an Object on the stack, with the top
 143    * most Object being at position 1, and each Object deeper in the
 144    * stack at depth + 1.
 145    *
 146    * @param o The object to search for
 147    * @return The 1 based depth of the Object, or -1 if the Object
 148    *         is not on the stack
 149    */
 150   public synchronized int search(Object o)
 151   {
 152     int i = elementCount;
 153     while (--i >= 0)
 154       if (equals(o, elementData[i]))
 155         return elementCount - i;
 156     return -1;
 157   }
 158 }