J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1994-2005 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package java.util; |
| 27 | |
| 28 | /** |
| 29 | * The <code>Stack</code> class represents a last-in-first-out |
| 30 | * (LIFO) stack of objects. It extends class <tt>Vector</tt> with five |
| 31 | * operations that allow a vector to be treated as a stack. The usual |
| 32 | * <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a |
| 33 | * method to <tt>peek</tt> at the top item on the stack, a method to test |
| 34 | * for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt> |
| 35 | * the stack for an item and discover how far it is from the top. |
| 36 | * <p> |
| 37 | * When a stack is first created, it contains no items. |
| 38 | * |
| 39 | * <p>A more complete and consistent set of LIFO stack operations is |
| 40 | * provided by the {@link Deque} interface and its implementations, which |
| 41 | * should be used in preference to this class. For example: |
| 42 | * <pre> {@code |
| 43 | * Deque<Integer> stack = new ArrayDeque<Integer>();}</pre> |
| 44 | * |
| 45 | * @author Jonathan Payne |
| 46 | * @since JDK1.0 |
| 47 | */ |
| 48 | public |
| 49 | class Stack<E> extends Vector<E> { |
| 50 | /** |
| 51 | * Creates an empty Stack. |
| 52 | */ |
| 53 | public Stack() { |
| 54 | } |
| 55 | |
| 56 | /** |
| 57 | * Pushes an item onto the top of this stack. This has exactly |
| 58 | * the same effect as: |
| 59 | * <blockquote><pre> |
| 60 | * addElement(item)</pre></blockquote> |
| 61 | * |
| 62 | * @param item the item to be pushed onto this stack. |
| 63 | * @return the <code>item</code> argument. |
| 64 | * @see java.util.Vector#addElement |
| 65 | */ |
| 66 | public E push(E item) { |
| 67 | addElement(item); |
| 68 | |
| 69 | return item; |
| 70 | } |
| 71 | |
| 72 | /** |
| 73 | * Removes the object at the top of this stack and returns that |
| 74 | * object as the value of this function. |
| 75 | * |
| 76 | * @return The object at the top of this stack (the last item |
| 77 | * of the <tt>Vector</tt> object). |
| 78 | * @exception EmptyStackException if this stack is empty. |
| 79 | */ |
| 80 | public synchronized E pop() { |
| 81 | E obj; |
| 82 | int len = size(); |
| 83 | |
| 84 | obj = peek(); |
| 85 | removeElementAt(len - 1); |
| 86 | |
| 87 | return obj; |
| 88 | } |
| 89 | |
| 90 | /** |
| 91 | * Looks at the object at the top of this stack without removing it |
| 92 | * from the stack. |
| 93 | * |
| 94 | * @return the object at the top of this stack (the last item |
| 95 | * of the <tt>Vector</tt> object). |
| 96 | * @exception EmptyStackException if this stack is empty. |
| 97 | */ |
| 98 | public synchronized E peek() { |
| 99 | int len = size(); |
| 100 | |
| 101 | if (len == 0) |
| 102 | throw new EmptyStackException(); |
| 103 | return elementAt(len - 1); |
| 104 | } |
| 105 | |
| 106 | /** |
| 107 | * Tests if this stack is empty. |
| 108 | * |
| 109 | * @return <code>true</code> if and only if this stack contains |
| 110 | * no items; <code>false</code> otherwise. |
| 111 | */ |
| 112 | public boolean empty() { |
| 113 | return size() == 0; |
| 114 | } |
| 115 | |
| 116 | /** |
| 117 | * Returns the 1-based position where an object is on this stack. |
| 118 | * If the object <tt>o</tt> occurs as an item in this stack, this |
| 119 | * method returns the distance from the top of the stack of the |
| 120 | * occurrence nearest the top of the stack; the topmost item on the |
| 121 | * stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt> |
| 122 | * method is used to compare <tt>o</tt> to the |
| 123 | * items in this stack. |
| 124 | * |
| 125 | * @param o the desired object. |
| 126 | * @return the 1-based position from the top of the stack where |
| 127 | * the object is located; the return value <code>-1</code> |
| 128 | * indicates that the object is not on the stack. |
| 129 | */ |
| 130 | public synchronized int search(Object o) { |
| 131 | int i = lastIndexOf(o); |
| 132 | |
| 133 | if (i >= 0) { |
| 134 | return size() - i; |
| 135 | } |
| 136 | return -1; |
| 137 | } |
| 138 | |
| 139 | /** use serialVersionUID from JDK 1.0.2 for interoperability */ |
| 140 | private static final long serialVersionUID = 1224463164541339165L; |
| 141 | } |