Java Data Structure How to - Create a faster, smaller stack implementation

• Back to Stack  ↑

Question

We would like to know how to create a faster, smaller stack implementation.

Answer

 //from   ww w.j a va 2s  .  c  o  m


/*
 * 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.
 */

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

/**
 * A faster, smaller stack implementation. ArrayListStack is final and unsynchronized (the JDK's
 * methods are synchronized). In addition you can set the initial capacity if you want via the
 * ArrayListStack(int) constructor.
 * 
 * @author Jonathan Locke
 * @param <T>
 */
public final class ArrayListStack<T> extends ArrayList<T>
{
  private static final long serialVersionUID = 1L;

  /**
   * Construct.
   * 
   * @param initialCapacity
   *            Initial capacity of the stack
   */
  public ArrayListStack(final int initialCapacity)
  {
    super(initialCapacity);
  }

  /**
   * Construct.
   */
  public ArrayListStack()
  {
    this(10);
  }

  /**
   * Construct.
   * 
   * @param collection
   *            The collection to add
   */
  public ArrayListStack(final Collection<T> collection)
  {
    super(collection);
  }

  /**
   * Pushes an item onto the top of this stack.
   * 
   * @param item
   *            the item to be pushed onto this stack.
   */
  public final void push(final T item)
  {
    add(item);
  }

  /**
   * Removes the object at the top of this stack and returns that object.
   * 
   * @return The object at the top of this stack
   * @exception EmptyStackException
   *                If this stack is empty.
   */
  public final T pop()
  {
    final T top = peek();
    remove(size() - 1);
    return top;
  }

  /**
   * Looks at the object at the top of this stack without removing it.
   * 
   * @return The object at the top of this stack
   * @exception EmptyStackException
   *                If this stack is empty.
   */
  public final T peek()
  {
    int size = size();
    if (size == 0)
    {
      throw new EmptyStackException();
    }
    return get(size - 1);
  }

  /**
   * Tests if this stack is empty.
   * 
   * @return <code>true if and only if this stack contains no items; <code>false
   *         otherwise.
   */
  public final boolean empty()
  {
    return size() == 0;
  }

  /**
   * Returns the 1-based position where an object is on this stack. If the object <tt>o</tt>
   * occurs as an item in this stack, this method returns the distance from the top of the stack
   * of the occurrence nearest the top of the stack; the topmost item on the stack is considered
   * to be at distance <tt>1</tt>. The <tt>equals</tt> method is used to compare <tt>o</tt>
   * to the items in this stack.
   * 
   * @param o
   *            the desired object.
   * @return the 1-based position from the top of the stack where the object is located; the
   *         return value <code>-1 indicates that the object is not on the stack.
   */
  public final int search(final T o)
  {
    int i = lastIndexOf(o);
    if (i >= 0)
    {
      return size() - i;
    }
    return -1;
  }
}

• Back to Stack  ↑