001: /*
002: *
003: *
004: * Copyright 1990-2007 Sun Microsystems, Inc. All Rights Reserved.
005: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
006: *
007: * This program is free software; you can redistribute it and/or
008: * modify it under the terms of the GNU General Public License version
009: * 2 only, as published by the Free Software Foundation.
010: *
011: * This program is distributed in the hope that it will be useful, but
012: * WITHOUT ANY WARRANTY; without even the implied warranty of
013: * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014: * General Public License version 2 for more details (a copy is
015: * included at /legal/license.txt).
016: *
017: * You should have received a copy of the GNU General Public License
018: * version 2 along with this work; if not, write to the Free Software
019: * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
020: * 02110-1301 USA
021: *
022: * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
023: * Clara, CA 95054 or visit www.sun.com if you need additional
024: * information or have any questions.
025: */
026:
027: package java.util;
028:
029: /**
030: * The <code>Stack</code> class represents a last-in-first-out
031: * (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
032: * operations that allow a vector to be treated as a stack. The usual
033: * <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
034: * method to <tt>peek</tt> at the top item on the stack, a method to test
035: * for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
036: * the stack for an item and discover how far it is from the top.
037: * <p>
038: * When a stack is first created, it contains no items.
039: *
040: * @version 12/17/01 (CLDC 1.1)
041: * @since JDK1.0, CLDC 1.0
042: */
043: public class Stack extends Vector {
044:
045: /**
046: * Creates an empty Stack.
047: */
048: public Stack() {
049: }
050:
051: /**
052: * Pushes an item onto the top of this stack. This has exactly
053: * the same effect as:
054: * <blockquote><pre>
055: * addElement(item)</pre></blockquote>
056: *
057: * @param item the item to be pushed onto this stack.
058: * @return the <code>item</code> argument.
059: * @see java.util.Vector#addElement
060: */
061: public Object push(Object item) {
062: addElement(item);
063: return item;
064: }
065:
066: /**
067: * Removes the object at the top of this stack and returns that
068: * object as the value of this function.
069: *
070: * @return The object at the top of this stack (the last item
071: * of the <tt>Vector</tt> object).
072: * @exception EmptyStackException if this stack is empty.
073: */
074: public synchronized Object pop() {
075: Object obj;
076: int len = size();
077:
078: obj = peek();
079: removeElementAt(len - 1);
080:
081: return obj;
082: }
083:
084: /**
085: * Looks at the object at the top of this stack without removing it
086: * from the stack.
087: *
088: * @return the object at the top of this stack (the last item
089: * of the <tt>Vector</tt> object).
090: * @exception EmptyStackException if this stack is empty.
091: */
092: public synchronized Object peek() {
093: int len = size();
094:
095: if (len == 0) {
096: throw new EmptyStackException();
097: }
098:
099: return elementAt(len - 1);
100: }
101:
102: /**
103: * Tests if this stack is empty.
104: *
105: * @return <code>true</code> if and only if this stack contains
106: * no items; <code>false</code> otherwise.
107: */
108: public boolean empty() {
109: return size() == 0;
110: }
111:
112: /**
113: * Returns the 1-based position where an object is on this stack.
114: * If the object <tt>o</tt> occurs as an item in this stack, this
115: * method returns the distance from the top of the stack of the
116: * occurrence nearest the top of the stack; the topmost item on the
117: * stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt>
118: * method is used to compare <tt>o</tt> to the
119: * items in this stack.
120: *
121: * @param o the desired object.
122: * @return the 1-based position from the top of the stack where
123: * the object is located; the return value <code>-1</code>
124: * indicates that the object is not on the stack.
125: */
126: public synchronized int search(Object o) {
127: int i = lastIndexOf(o);
128:
129: if (i >= 0) {
130: return size() - i;
131: }
132:
133: return -1;
134: }
135:
136: }
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