    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4;
    018
    019import java.util.ArrayList;
    020import java.util.EmptyStackException;
    021
    022/**
    023 * An implementation of the {@link java.util.Stack} API that is based on an
    024 * {@code ArrayList} instead of a {@code Vector}, so it is not
    025 * synchronized to protect against multithreaded access.  The implementation
    026 * is therefore operates faster in environments where you do not need to
    027 * worry about multiple thread contention.
    028 * <p>
    029 * The removal order of an {@code ArrayStack} is based on insertion
    030 * order: The most recently added element is removed first.  The iteration
    031 * order is <em>not</em> the same as the removal order.  The iterator returns
    032 * elements from the bottom up.
    033 * </p>
    034 * <p>
    035 * Unlike {@code Stack}, {@code ArrayStack} accepts null entries.
    036 * <p>
    037 * <strong>Note:</strong> From version 4.0 onwards, this class does not implement the
    038 * removed {@code Buffer} interface anymore.
    039 * </p>
    040 *
    041 * @param <E> the type of elements in this list
    042 * @see java.util.Stack
    043 * @since 1.0
    044 * @deprecated use {@link java.util.ArrayDeque} instead (available from Java 1.6)
    045 */
    046@Deprecated
    047public class ArrayStack<E> extends ArrayList<E> {
    048
    049    /** Ensure serialization compatibility */
    050    private static final long serialVersionUID = 2130079159931574599L;
    051
    052    /**
    053     * Constructs a new empty {@code ArrayStack}. The initial size
    054     * is controlled by {@code ArrayList} and is currently 10.
    055     */
    056    public ArrayStack() {
    057    }
    058
    059    /**
    060     * Constructs a new empty {@code ArrayStack} with an initial size.
    061     *
    062     * @param initialSize  the initial size to use
    063     * @throws IllegalArgumentException  if the specified initial size
    064     *  is negative
    065     */
    066    public ArrayStack(final int initialSize) {
    067        super(initialSize);
    068    }
    069
    070    /**
    071     * Return {@code true} if this stack is currently empty.
    072     * <p>
    073     * This method exists for compatibility with {@link java.util.Stack}.
    074     * New users of this class should use {@code isEmpty} instead.
    075     * </p>
    076     *
    077     * @return true if the stack is currently empty
    078     */
    079    public boolean empty() {
    080        return isEmpty();
    081    }
    082
    083    /**
    084     * Returns the top item off of this stack without removing it.
    085     *
    086     * @return the top item on the stack
    087     * @throws EmptyStackException  if the stack is empty
    088     */
    089    public E peek() throws EmptyStackException {
    090        final int n = size();
    091        if (n <= 0) {
    092            throw new EmptyStackException();
    093        }
    094        return get(n - 1);
    095    }
    096
    097    /**
    098     * Returns the n'th item down (zero-relative) from the top of this
    099     * stack without removing it.
    100     *
    101     * @param n  the number of items down to go
    102     * @return the n'th item on the stack, zero relative
    103     * @throws EmptyStackException  if there are not enough items on the
    104     *  stack to satisfy this request
    105     */
    106    public E peek(final int n) throws EmptyStackException {
    107        final int m = size() - n - 1;
    108        if (m < 0) {
    109            throw new EmptyStackException();
    110        }
    111        return get(m);
    112    }
    113
    114    /**
    115     * Pops the top item off of this stack and return it.
    116     *
    117     * @return the top item on the stack
    118     * @throws EmptyStackException  if the stack is empty
    119     */
    120    public E pop() throws EmptyStackException {
    121        final int n = size();
    122        if (n <= 0) {
    123            throw new EmptyStackException();
    124        }
    125        return remove(n - 1);
    126    }
    127
    128    /**
    129     * Pushes a new item onto the top of this stack. The pushed item is also
    130     * returned. This is equivalent to calling {@code add}.
    131     *
    132     * @param item  the item to be added
    133     * @return the item just pushed
    134     */
    135    public E push(final E item) {
    136        add(item);
    137        return item;
    138    }
    139
    140    /**
    141     * Returns the one-based position of the distance from the top that the
    142     * specified object exists on this stack, where the top-most element is
    143     * considered to be at distance {@code 1}.  If the object is not
    144     * present on the stack, return {@code -1} instead.  The
    145     * {@code equals()} method is used to compare to the items
    146     * in this stack.
    147     *
    148     * @param object  the object to be searched for
    149     * @return the 1-based depth into the stack of the object, or -1 if not found
    150     */
    151    public int search(final Object object) {
    152        int i = size() - 1;        // Current index
    153        int n = 1;                 // Current distance
    154        while (i >= 0) {
    155            final Object current = get(i);
    156            if (object == null && current == null ||
    157                object != null && object.equals(current)) {
    158                return n;
    159            }
    160            i--;
    161            n++;
    162        }
    163        return -1;
    164    }
    165
    166}