*

 * 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.tomcat.util.digester;

import java.util.ArrayList;

import java.util.EmptyStackException;

/**

 * <p>Imported copy of the <code>ArrayStack</code> class from

 * Commons Collections, which was the only direct dependency from Digester.</p>

 *

 * <p><strong>WARNNG</strong> - This class is public solely to allow it to be

 * used from subpackages of <code>org.apache.commons.digester</code>.

 * It should not be considered part of the public API of Commons Digester.

 * If you want to use such a class yourself, you should use the one from

 * Commons Collections directly.</p>

 *

 * <p>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>

 *

 * <p>Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.

 * </p>

 *

 * @see java.util.Stack

 * @since Digester 1.6 (from Commons Collections 1.0)

 */

public class ArrayStack extends ArrayList {

    /** Ensure serialization compatibility */    

    private static final long serialVersionUID = 2130079159931574599L;

    /**

     * 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 <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 <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.

     *

     * @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.

     *

     * @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.

     *

     * @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 <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 <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;

    }

}