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, 2005 Free Software Foundation, Inc.
5 This file is part of GNU Classpath.
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)
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.
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., 51 Franklin Street, Fifth Floor, Boston, MA
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
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. */
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
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.
53 * @author Warren Levy (warrenl@cygnus.com)
54 * @author Eric Blake (ebb9@email.byu.edu)
59 * @status updated to 1.4
61 public class Stack
extends Vector
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).
68 * Compatible with JDK 1.0+.
70 private static final long serialVersionUID
= 1224463164541339165L;
73 * This constructor creates a new Stack, initially empty
80 * Pushes an Object onto the top of the stack. This method is effectively
81 * the same as addElement(item).
83 * @param item the Object to push onto the stack
84 * @return the Object pushed onto the stack
85 * @see Vector#addElement(Object)
87 public Object
push(Object item
)
89 // When growing the Stack, use the Vector routines in case more
91 // Note: spec indicates that this method *always* returns obj passed in!
98 * Pops an item from the stack and returns it. The item popped is
99 * removed from the Stack.
101 * @return the Object popped from the stack
102 * @throws EmptyStackException if the stack is empty
104 public synchronized Object
pop()
106 if (elementCount
== 0)
107 throw new EmptyStackException();
110 Object obj
= elementData
[--elementCount
];
112 // Set topmost element to null to assist the gc in cleanup.
113 elementData
[elementCount
] = null;
118 * Returns the top Object on the stack without removing it.
120 * @return the top Object on the stack
121 * @throws EmptyStackException if the stack is empty
123 public synchronized Object
peek()
125 if (elementCount
== 0)
126 throw new EmptyStackException();
128 return elementData
[elementCount
- 1];
132 * Tests if the stack is empty.
134 * @return true if the stack contains no items, false otherwise
136 public synchronized boolean empty()
138 return elementCount
== 0;
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.
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
150 public synchronized int search(Object o
)
152 int i
= elementCount
;
154 if (equals(o
, elementData
[i
]))
155 return elementCount
- i
;