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 */ Stack()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 */ push(E item)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 */ pop()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 */ peek()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 */ empty()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 */ search(Object o)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 } 142