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142 lines
3.8 KiB
142 lines
3.8 KiB
/*
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* Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*/
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package java.util;
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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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* 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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return item;
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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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obj = peek();
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removeElementAt(len - 1);
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return obj;
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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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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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* 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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* 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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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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/** use serialVersionUID from JDK 1.0.2 for interoperability */
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private static final long serialVersionUID = 1224463164541339165L;
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}
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