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}