| 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 |
* @version %I%, %G% |
| 47 |
* @since JDK1.0 |
| 48 |
*/ |
| 49 |
public |
| 50 |
class Stack<E> extends Vector<E> { |
| 51 |
/** |
| 52 |
* Creates an empty Stack. |
| 53 |
*/ |
| 54 |
public Stack() { |
| 55 |
} |
| 56 |
|
| 57 |
/** |
| 58 |
* Pushes an item onto the top of this stack. This has exactly |
| 59 |
* the same effect as: |
| 60 |
* <blockquote><pre> |
| 61 |
* addElement(item)</pre></blockquote> |
| 62 |
* |
| 63 |
* @param item the item to be pushed onto this stack. |
| 64 |
* @return the <code>item</code> argument. |
| 65 |
* @see java.util.Vector#addElement |
| 66 |
*/ |
| 67 |
public E push(E item) { |
| 68 |
addElement(item); |
| 69 |
|
| 70 |
return item; |
| 71 |
} |
| 72 |
|
| 73 |
/** |
| 74 |
* Removes the object at the top of this stack and returns that |
| 75 |
* object as the value of this function. |
| 76 |
* |
| 77 |
* @return The object at the top of this stack (the last item |
| 78 |
* of the <tt>Vector</tt> object). |
| 79 |
* @exception EmptyStackException if this stack is empty. |
| 80 |
*/ |
| 81 |
public synchronized E pop() { |
| 82 |
E obj; |
| 83 |
int len = size(); |
| 84 |
|
| 85 |
obj = peek(); |
| 86 |
removeElementAt(len - 1); |
| 87 |
|
| 88 |
return obj; |
| 89 |
} |
| 90 |
|
| 91 |
/** |
| 92 |
* Looks at the object at the top of this stack without removing it |
| 93 |
* from the stack. |
| 94 |
* |
| 95 |
* @return the object at the top of this stack (the last item |
| 96 |
* of the <tt>Vector</tt> object). |
| 97 |
* @exception EmptyStackException if this stack is empty. |
| 98 |
*/ |
| 99 |
public synchronized E peek() { |
| 100 |
int len = size(); |
| 101 |
|
| 102 |
if (len == 0) |
| 103 |
throw new EmptyStackException(); |
| 104 |
return elementAt(len - 1); |
| 105 |
} |
| 106 |
|
| 107 |
/** |
| 108 |
* Tests if this stack is empty. |
| 109 |
* |
| 110 |
* @return <code>true</code> if and only if this stack contains |
| 111 |
* no items; <code>false</code> otherwise. |
| 112 |
*/ |
| 113 |
public boolean empty() { |
| 114 |
return size() == 0; |
| 115 |
} |
| 116 |
|
| 117 |
/** |
| 118 |
* Returns the 1-based position where an object is on this stack. |
| 119 |
* If the object <tt>o</tt> occurs as an item in this stack, this |
| 120 |
* method returns the distance from the top of the stack of the |
| 121 |
* occurrence nearest the top of the stack; the topmost item on the |
| 122 |
* stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt> |
| 123 |
* method is used to compare <tt>o</tt> to the |
| 124 |
* items in this stack. |
| 125 |
* |
| 126 |
* @param o the desired object. |
| 127 |
* @return the 1-based position from the top of the stack where |
| 128 |
* the object is located; the return value <code>-1</code> |
| 129 |
* indicates that the object is not on the stack. |
| 130 |
*/ |
| 131 |
public synchronized int search(Object o) { |
| 132 |
int i = lastIndexOf(o); |
| 133 |
|
| 134 |
if (i >= 0) { |
| 135 |
return size() - i; |
| 136 |
} |
| 137 |
return -1; |
| 138 |
} |
| 139 |
|
| 140 |
/** use serialVersionUID from JDK 1.0.2 for interoperability */ |
| 141 |
private static final long serialVersionUID = 1224463164541339165L; |
| 142 |
} |
