001: /*
002: * Copyright 1994-2005 Sun Microsystems, Inc. All Rights Reserved.
003: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004: *
005: * This code is free software; you can redistribute it and/or modify it
006: * under the terms of the GNU General Public License version 2 only, as
007: * published by the Free Software Foundation. Sun designates this
008: * particular file as subject to the "Classpath" exception as provided
009: * by Sun in the LICENSE file that accompanied this code.
010: *
011: * This code is distributed in the hope that it will be useful, but WITHOUT
012: * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013: * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014: * version 2 for more details (a copy is included in the LICENSE file that
015: * accompanied this code).
016: *
017: * You should have received a copy of the GNU General Public License version
018: * 2 along with this work; if not, write to the Free Software Foundation,
019: * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020: *
021: * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022: * CA 95054 USA or visit www.sun.com if you need additional information or
023: * have any questions.
024: */
025:
026: package java.util;
027:
028: /**
029: * The <code>Stack</code> class represents a last-in-first-out
030: * (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
031: * operations that allow a vector to be treated as a stack. The usual
032: * <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
033: * method to <tt>peek</tt> at the top item on the stack, a method to test
034: * for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
035: * the stack for an item and discover how far it is from the top.
036: * <p>
037: * When a stack is first created, it contains no items.
038: *
039: * <p>A more complete and consistent set of LIFO stack operations is
040: * provided by the {@link Deque} interface and its implementations, which
041: * should be used in preference to this class. For example:
042: * <pre> {@code
043: * Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
044: *
045: * @author Jonathan Payne
046: * @version 1.36, 05/05/07
047: * @since JDK1.0
048: */
049: public class Stack<E> extends Vector<E> {
050: /**
051: * Creates an empty Stack.
052: */
053: public Stack() {
054: }
055:
056: /**
057: * Pushes an item onto the top of this stack. This has exactly
058: * the same effect as:
059: * <blockquote><pre>
060: * addElement(item)</pre></blockquote>
061: *
062: * @param item the item to be pushed onto this stack.
063: * @return the <code>item</code> argument.
064: * @see java.util.Vector#addElement
065: */
066: public E push(E item) {
067: addElement(item);
068:
069: return item;
070: }
071:
072: /**
073: * Removes the object at the top of this stack and returns that
074: * object as the value of this function.
075: *
076: * @return The object at the top of this stack (the last item
077: * of the <tt>Vector</tt> object).
078: * @exception EmptyStackException if this stack is empty.
079: */
080: public synchronized E pop() {
081: E obj;
082: int len = size();
083:
084: obj = peek();
085: removeElementAt(len - 1);
086:
087: return obj;
088: }
089:
090: /**
091: * Looks at the object at the top of this stack without removing it
092: * from the stack.
093: *
094: * @return the object at the top of this stack (the last item
095: * of the <tt>Vector</tt> object).
096: * @exception EmptyStackException if this stack is empty.
097: */
098: public synchronized E peek() {
099: 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: }
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