/** Here is an alternative implementation of a stack using an ArrayList
 *  in case we'd like to switch.
 */
import java.util.*;

public class ArrayListStack implements StackInterface
{
  private ArrayList list;

  public ArrayListStack()
  {
    list = new ArrayList();
  }

  public void push(Object o)
  {
    list.add(o);
  }

  public Object pop()
  {
    Object victim = peek();
    list.remove(list.size() - 1);
    return victim;
  }

  public Object peek()
  {
    return list.get(list.size() - 1);
  }

  public int size()
  {
    return list.size();
  }

  // We want to show the top (end) of the stack on top, so we start the
  // iterator at the end, at position = size.  Note it's not size - 1,
  // because the position of an iterator is defined to be which element
  // would be returned if we call next().
  // To go backwards thru the list, we call hasPrevious() and previous().
  public String toString()
  {
    String build = "";
    /*
    for (int i = list.size() - 1; i >= 0; --i)
    {
      build += "\t" + list.get(i) + "\n";
    }
    */

    ListIterator iter = list.listIterator(list.size());
    while (iter.hasPrevious())
      build += "\t" + iter.previous() + "\n";
    return build;
  }
}