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92aaa24628
From-SVN: r49104
159 lines
4.9 KiB
Java
159 lines
4.9 KiB
Java
/* Stack.java - Class that provides a Last In First Out (LIFO)
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datatype, known more commonly as a Stack
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Copyright (C) 1998, 1999, 2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.util;
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/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
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* "The Java Language Specification", ISBN 0-201-63451-1
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* plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
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* Status: Believed complete and correct
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/**
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* Stack provides a Last In First Out (LIFO) data type, commonly known
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* as a Stack. Stack itself extends Vector and provides the additional
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* methods for stack manipulation (push, pop, peek). You can also seek for
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* the 1-based position of an element on the stack.
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*
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* @author Warren Levy <warrenl@cygnus.com>
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* @author Eric Blake <ebb9@email.byu.edu>
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* @see List
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* @see AbstractList
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* @see LinkedList
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* @since 1.0
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* @status updated to 1.4
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*/
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public class Stack extends Vector
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{
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// We could use Vector methods internally for the following methods,
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// but have used Vector fields directly for efficiency (i.e. this
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// often reduces out duplicate bounds checking).
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/**
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* Compatible with JDK 1.0+.
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*/
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private static final long serialVersionUID = 1224463164541339165L;
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/**
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* This constructor creates a new Stack, initially empty
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*/
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public Stack()
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{
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}
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/**
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* Pushes an Object onto the top of the stack. This method is effectively
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* the same as addElement(item).
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*
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* @param item the Object to push onto the stack
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* @return the Object pushed onto the stack
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* @see Vector#addElement(Object)
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*/
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public Object push(Object item)
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{
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// When growing the Stack, use the Vector routines in case more
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// memory is needed.
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// Note: spec indicates that this method *always* returns obj passed in!
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addElement(item);
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return item;
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}
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/**
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* Pops an item from the stack and returns it. The item popped is
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* removed from the Stack.
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*
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* @return the Object popped from the stack
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* @throws EmptyStackException if the stack is empty
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*/
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public synchronized Object pop()
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{
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if (elementCount == 0)
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throw new EmptyStackException();
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modCount++;
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Object obj = elementData[--elementCount];
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// Set topmost element to null to assist the gc in cleanup.
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elementData[elementCount] = null;
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return obj;
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}
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/**
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* Returns the top Object on the stack without removing it.
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*
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* @return the top Object on the stack
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* @throws EmptyStackException if the stack is empty
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*/
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public synchronized Object peek()
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{
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if (elementCount == 0)
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throw new EmptyStackException();
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return elementData[elementCount - 1];
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}
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/**
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* Tests if the stack is empty.
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*
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* @return true if the stack contains no items, false otherwise
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*/
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public synchronized boolean empty()
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{
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return elementCount == 0;
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}
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/**
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* Returns the position of an Object on the stack, with the top
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* most Object being at position 1, and each Object deeper in the
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* stack at depth + 1.
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*
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* @param o The object to search for
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* @return The 1 based depth of the Object, or -1 if the Object
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* is not on the stack
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*/
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public synchronized int search(Object o)
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{
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int i = elementCount;
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while (--i >= 0)
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if (equals(o, elementData[i]))
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return elementCount - i;
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return -1;
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}
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}
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