/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.commons.collections;

import java.util.ArrayList;
import java.util.EmptyStackException;

An implementation of the Stack API that is based on an ArrayList instead of a Vector, so it is not
synchronized to protect against multi-threaded access.  The implementation
is therefore operates faster in environments where you do not need to
worry about multiple thread contention.

The removal order of an ArrayStack is based on insertion 
order: The most recently added element is removed first.  The iteration
order is not the same as the removal order. The iterator returns elements from the bottom up, whereas the remove() method removes them from the top down. 

Unlike Stack, ArrayStack accepts null entries.
Author:
Craig R. McClanahan, Paul Jack, Stephen Colebourne
See Also:
Stack
Since:
Commons Collections 1.0
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $/**
 * An implementation of the {@link java.util.Stack} API that is based on an
 * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not
 * synchronized to protect against multi-threaded access.  The implementation
 * is therefore operates faster in environments where you do not need to
 * worry about multiple thread contention.
 * <p>
 * The removal order of an <code>ArrayStack</code> is based on insertion 
 * order: The most recently added element is removed first.  The iteration
 * order is <i>not</i> the same as the removal order.  The iterator returns
 * elements from the bottom up, whereas the {@link #remove()} method removes
 * them from the top down.
 * <p>
 * Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
 *
 * @see java.util.Stack
 * @since Commons Collections 1.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
 * 
 * @author Craig R. McClanahan
 * @author Paul Jack
 * @author Stephen Colebourne
 */
public class ArrayStack extends ArrayList implements Buffer {

    
Ensure serialization compatibility /** Ensure serialization compatibility */    
    private static final long serialVersionUID = 2130079159931574599L;

    
Constructs a new empty ArrayStack. The initial size
is controlled by ArrayList and is currently 10.
/**
     * Constructs a new empty <code>ArrayStack</code>. The initial size
     * is controlled by <code>ArrayList</code> and is currently 10.
     */
    public ArrayStack() {
        super();
    }

    
Constructs a new empty ArrayStack with an initial size.
Params:
initialSize –  the initial size to use
Throws:
IllegalArgumentException –  if the specified initial size
 is negative/**
     * Constructs a new empty <code>ArrayStack</code> with an initial size.
     * 
     * @param initialSize  the initial size to use
     * @throws IllegalArgumentException  if the specified initial size
     *  is negative
     */
    public ArrayStack(int initialSize) {
        super(initialSize);
    }

    
Return true if this stack is currently empty.

This method exists for compatibility with java.util.Stack.
New users of this class should use isEmpty instead.
Returns:
true if the stack is currently empty/**
     * Return <code>true</code> if this stack is currently empty.
     * <p>
     * This method exists for compatibility with <code>java.util.Stack</code>.
     * New users of this class should use <code>isEmpty</code> instead.
     * 
     * @return true if the stack is currently empty
     */
    public boolean empty() {
        return isEmpty();
    }

    
Returns the top item off of this stack without removing it.
Throws:
EmptyStackException –  if the stack is empty
Returns:
the top item on the stack/**
     * Returns the top item off of this stack without removing it.
     *
     * @return the top item on the stack
     * @throws EmptyStackException  if the stack is empty
     */
    public Object peek() throws EmptyStackException {
        int n = size();
        if (n <= 0) {
            throw new EmptyStackException();
        } else {
            return get(n - 1);
        }
    }

    
Returns the n'th item down (zero-relative) from the top of this
stack without removing it.
Params:
n –  the number of items down to go
Throws:
EmptyStackException –  if there are not enough items on the
 stack to satisfy this request
Returns:
the n'th item on the stack, zero relative/**
     * Returns the n'th item down (zero-relative) from the top of this
     * stack without removing it.
     *
     * @param n  the number of items down to go
     * @return the n'th item on the stack, zero relative
     * @throws EmptyStackException  if there are not enough items on the
     *  stack to satisfy this request
     */
    public Object peek(int n) throws EmptyStackException {
        int m = (size() - n) - 1;
        if (m < 0) {
            throw new EmptyStackException();
        } else {
            return get(m);
        }
    }

    
Pops the top item off of this stack and return it.
Throws:
EmptyStackException –  if the stack is empty
Returns:
the top item on the stack/**
     * Pops the top item off of this stack and return it.
     *
     * @return the top item on the stack
     * @throws EmptyStackException  if the stack is empty
     */
    public Object pop() throws EmptyStackException {
        int n = size();
        if (n <= 0) {
            throw new EmptyStackException();
        } else {
            return remove(n - 1);
        }
    }

    
Pushes a new item onto the top of this stack. The pushed item is also
returned. This is equivalent to calling add.
Params:
item –  the item to be added
Returns:
the item just pushed/**
     * Pushes a new item onto the top of this stack. The pushed item is also
     * returned. This is equivalent to calling <code>add</code>.
     *
     * @param item  the item to be added
     * @return the item just pushed
     */
    public Object push(Object item) {
        add(item);
        return item;
    }

    
Returns the one-based position of the distance from the top that the
specified object exists on this stack, where the top-most element is
considered to be at distance 1.  If the object is not
present on the stack, return -1 instead.  The
equals() method is used to compare to the items
in this stack.
Params:
object –  the object to be searched for
Returns:
the 1-based depth into the stack of the object, or -1 if not found/**
     * Returns the one-based position of the distance from the top that the
     * specified object exists on this stack, where the top-most element is
     * considered to be at distance <code>1</code>.  If the object is not
     * present on the stack, return <code>-1</code> instead.  The
     * <code>equals()</code> method is used to compare to the items
     * in this stack.
     *
     * @param object  the object to be searched for
     * @return the 1-based depth into the stack of the object, or -1 if not found
     */
    public int search(Object object) {
        int i = size() - 1;        // Current index
        int n = 1;                 // Current distance
        while (i >= 0) {
            Object current = get(i);
            if ((object == null && current == null) ||
                (object != null && object.equals(current))) {
                return n;
            }
            i--;
            n++;
        }
        return -1;
    }

    
Returns the element on the top of the stack.
Throws:
BufferUnderflowException –  if the stack is empty
Returns:
the element on the top of the stack/**
     * Returns the element on the top of the stack.
     *
     * @return the element on the top of the stack
     * @throws BufferUnderflowException  if the stack is empty
     */
    public Object get() {
        int size = size();
        if (size == 0) {
            throw new BufferUnderflowException();
        }
        return get(size - 1);
    }

    
Removes the element on the top of the stack.
Throws:
BufferUnderflowException –  if the stack is empty
Returns:
the removed element/**
     * Removes the element on the top of the stack.
     *
     * @return the removed element 
     * @throws BufferUnderflowException  if the stack is empty
     */
    public Object remove() {
        int size = size();
        if (size == 0) {
            throw new BufferUnderflowException();
        }
        return remove(size - 1);
    }

}