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| 1 | +/* | |
| 2 | + * Copyright (c) 1994, 2010, Oracle and/or its affiliates. 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. Oracle designates this | |
| 8 | + * particular file as subject to the "Classpath" exception as provided | |
| 9 | + * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 22 | + * or visit www.oracle.com if you need additional information or have any | |
| 23 | + * 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 | + * @throws 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 | + * @throws 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 | +} | |