    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 *      https://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.ArrayDeque;
    020import java.util.ArrayList;
    021import java.util.EmptyStackException;
    022import java.util.Stack;
    023
    024/**
    025 * An implementation of the {@link Stack} API that is based on an
    026 * {@code ArrayList} instead of a {@code Vector}, so it is not
    027 * synchronized to protect against multithreaded access.  The implementation
    028 * is therefore operates faster in environments where you do not need to
    029 * worry about multiple thread contention.
    030 * <p>
    031 * The removal order of an {@code ArrayStack} is based on insertion
    032 * order: The most recently added element is removed first.  The iteration
    033 * order is <em>not</em> the same as the removal order.  The iterator returns
    034 * elements from the bottom up.
    035 * </p>
    036 * <p>
    037 * Unlike {@code Stack}, {@code ArrayStack} accepts null entries.
    038 * <p>
    039 * <strong>Note:</strong> From version 4.0 onwards, this class does not implement the
    040 * removed {@code Buffer} interface anymore.
    041 * </p>
    042 *
    043 * @param <E> The type of elements in this list
    044 * @see java.util.Stack
    045 * @since 1.0
    046 * @deprecated Use {@link ArrayDeque} instead (available from Java 1.6)
    047 */
    048@Deprecated
    049public class ArrayStack<E> extends ArrayList<E> {
    050
    051    /** Ensure serialization compatibility */
    052    private static final long serialVersionUID = 2130079159931574599L;
    053
    054    /**
    055     * Constructs a new empty {@code ArrayStack}. The initial size
    056     * is controlled by {@code ArrayList} and is currently 10.
    057     */
    058    public ArrayStack() {
    059    }
    060
    061    /**
    062     * Constructs a new empty {@code ArrayStack} with an initial size.
    063     *
    064     * @param initialSize  The initial size to use
    065     * @throws IllegalArgumentException  if the specified initial size
    066     *  is negative
    067     */
    068    public ArrayStack(final int initialSize) {
    069        super(initialSize);
    070    }
    071
    072    /**
    073     * Return {@code true} if this stack is currently empty.
    074     * <p>
    075     * This method exists for compatibility with {@link Stack}.
    076     * New users of this class should use {@code isEmpty} instead.
    077     * </p>
    078     *
    079     * @return true if the stack is currently empty
    080     */
    081    public boolean empty() {
    082        return isEmpty();
    083    }
    084
    085    /**
    086     * Returns the top item off of this stack without removing it.
    087     *
    088     * @return The top item on the stack
    089     * @throws EmptyStackException  if the stack is empty
    090     */
    091    public E peek() throws EmptyStackException {
    092        final int n = size();
    093        if (n <= 0) {
    094            throw new EmptyStackException();
    095        }
    096        return get(n - 1);
    097    }
    098
    099    /**
    100     * Returns the n'th item down (zero-relative) from the top of this
    101     * stack without removing it.
    102     *
    103     * @param n  The number of items down to go
    104     * @return The n'th item on the stack, zero relative
    105     * @throws EmptyStackException  if there are not enough items on the
    106     *  stack to satisfy this request
    107     */
    108    public E peek(final int n) throws EmptyStackException {
    109        final int m = size() - n - 1;
    110        if (m < 0) {
    111            throw new EmptyStackException();
    112        }
    113        return get(m);
    114    }
    115
    116    /**
    117     * Pops the top item off of this stack and return it.
    118     *
    119     * @return The top item on the stack
    120     * @throws EmptyStackException  if the stack is empty
    121     */
    122    public E pop() throws EmptyStackException {
    123        final int n = size();
    124        if (n <= 0) {
    125            throw new EmptyStackException();
    126        }
    127        return remove(n - 1);
    128    }
    129
    130    /**
    131     * Pushes a new item onto the top of this stack. The pushed item is also
    132     * returned. This is equivalent to calling {@code add}.
    133     *
    134     * @param item  The item to be added
    135     * @return The item just pushed
    136     */
    137    public E push(final E item) {
    138        add(item);
    139        return item;
    140    }
    141
    142    /**
    143     * Returns the one-based position of the distance from the top that the
    144     * specified object exists on this stack, where the top-most element is
    145     * considered to be at distance {@code 1}.  If the object is not
    146     * present on the stack, return {@code -1} instead.  The
    147     * {@code equals()} method is used to compare to the items
    148     * in this stack.
    149     *
    150     * @param object  The object to be searched for
    151     * @return The 1-based depth into the stack of the object, or -1 if not found
    152     */
    153    public int search(final Object object) {
    154        int i = size() - 1;        // Current index
    155        int n = 1;                 // Current distance
    156        while (i >= 0) {
    157            final Object current = get(i);
    158            if (object == null && current == null ||
    159                object != null && object.equals(current)) {
    160                return n;
    161            }
    162            i--;
    163            n++;
    164        }
    165        return -1;
    166    }
    167
    168}