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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 | } | ||