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/* |
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* Copyright (c) 1994, 2005, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Sun designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Sun in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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|
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package java.util; |
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|
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/** |
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* The <code>Stack</code> class represents a last-in-first-out |
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* (LIFO) stack of objects. It extends class <tt>Vector</tt> with five |
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* operations that allow a vector to be treated as a stack. The usual |
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* <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a |
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* method to <tt>peek</tt> at the top item on the stack, a method to test |
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* for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt> |
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* the stack for an item and discover how far it is from the top. |
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* <p> |
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* When a stack is first created, it contains no items. |
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* |
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* <p>A more complete and consistent set of LIFO stack operations is |
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* provided by the {@link Deque} interface and its implementations, which |
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* should be used in preference to this class. For example: |
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* <pre> {@code |
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* Deque<Integer> stack = new ArrayDeque<Integer>();}</pre> |
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* |
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* @author Jonathan Payne |
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* @since JDK1.0 |
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*/ |
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public |
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class Stack<E> extends Vector<E> { |
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/** |
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* Creates an empty Stack. |
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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 item onto the top of this stack. This has exactly |
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* the same effect as: |
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* <blockquote><pre> |
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* addElement(item)</pre></blockquote> |
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* |
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* @param item the item to be pushed onto this stack. |
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* @return the <code>item</code> argument. |
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* @see java.util.Vector#addElement |
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*/ |
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public E push(E item) { |
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addElement(item); |
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|
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return item; |
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} |
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|
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/** |
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* Removes the object at the top of this stack and returns that |
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* object as the value of this function. |
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* |
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* @return The object at the top of this stack (the last item |
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* of the <tt>Vector</tt> object). |
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* @throws EmptyStackException if this stack is empty. |
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*/ |
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public synchronized E pop() { |
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E obj; |
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int len = size(); |
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|
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obj = peek(); |
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removeElementAt(len - 1); |
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|
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return obj; |
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} |
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|
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/** |
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* Looks at the object at the top of this stack without removing it |
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* from the stack. |
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* |
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* @return the object at the top of this stack (the last item |
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* of the <tt>Vector</tt> object). |
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* @throws EmptyStackException if this stack is empty. |
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*/ |
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public synchronized E peek() { |
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int len = size(); |
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|
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if (len == 0) |
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throw new EmptyStackException(); |
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return elementAt(len - 1); |
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} |
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|
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/** |
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* Tests if this stack is empty. |
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* |
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* @return <code>true</code> if and only if this stack contains |
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* no items; <code>false</code> otherwise. |
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*/ |
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public boolean empty() { |
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return size() == 0; |
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} |
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|
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/** |
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* Returns the 1-based position where an object is on this stack. |
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* If the object <tt>o</tt> occurs as an item in this stack, this |
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* method returns the distance from the top of the stack of the |
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* occurrence nearest the top of the stack; the topmost item on the |
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* stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt> |
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* method is used to compare <tt>o</tt> to the |
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* items in this stack. |
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* |
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* @param o the desired object. |
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* @return the 1-based position from the top of the stack where |
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* the object is located; the return value <code>-1</code> |
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* indicates that the object is not on the stack. |
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*/ |
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public synchronized int search(Object o) { |
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int i = lastIndexOf(o); |
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|
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if (i >= 0) { |
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return size() - i; |
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} |
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return -1; |
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} |
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|
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/** use serialVersionUID from JDK 1.0.2 for interoperability */ |
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private static final long serialVersionUID = 1224463164541339165L; |
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} |
