2
+ − 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 }