75 lines
1.9 KiB
Java
75 lines
1.9 KiB
Java
/* Copyright (C) 1998, 1999 Cygnus Solutions
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This file is part of libgcj.
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This software is copyrighted work licensed under the terms of the
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Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
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details. */
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package java.util;
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/**
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* @author Warren Levy <warrenl@cygnus.com>
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* @date August 20, 1998.
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*/
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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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public class Stack extends Vector
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{
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// 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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public boolean empty()
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{
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return elementCount == 0;
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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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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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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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public Object push(Object obj)
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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(obj);
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return obj;
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}
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public synchronized int search(Object obj)
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{
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// Return the position of obj on the stack as measured from the top;
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// i.e. the top element is 1, the next element down is 2, etc.
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// If obj is not on the stack, return -1
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for (int i = elementCount-1; i >=0; --i)
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if (elementData[i].equals(obj))
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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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