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
26package 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 */
48public
49class 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}
142