import java.util.Vector;

/**
 * An implementation of stacks that uses vectors.
 *
 * @author Samuel A. Rebelsky
 */
public class VectorBasedStack
  implements Stack
{
  // +-------+---------------------------------------------------
  // | Notes |
  // +-------+

  // +-----------+-----------------------------------------------
  // | Constants |
  // +-----------+

  // +--------+--------------------------------------------------
  // | Fields |
  // +--------+

  /**
   * The actual contents of the list, stored in a Vector.
   */
  Vector contents;


  // +--------------+--------------------------------------------
  // | Constructors |
  // +--------------+

  /**
   * Build an empty list.
   */
  public VectorBasedStack()
  {
    this.contents = new Vector();
  } // VectorBasedStack()

  // +------------------+----------------------------------------
  // | Exported Methods |
  // +------------------+

  /**
   * Determine if the stack is empty
   */
  public boolean isEmpty()
  {
    return this.contents.isEmpty();
  } // isEmpty()

  /**
   * Add an element to the stack.
   */
  public void add(Object newThingy) {
    this.contents.add(newThingy);
  } // add(Object)

  /**
   * Update the list by removing the last element in the vector.  Return
   * that element.
   */
  public Object get()
  {
    return this.contents.remove(last());
  } // get()

  public Object peek()
  {
    return this.contents.get(last());
  } // peek()


  // Find the position of the last element in the vector
  private int last(){
    if (this.contents.size() >= 1)
      return (this.contents.size() - 1);
    return (this.contents.size() - 1);	
  }//last()

  /**
   * Get the length.
   */
  public int length() 
  {
    return this.contents.size();
  } // length()

  /**
   * Convert to a string for ease of printing.
   */
  public String toString()
  {
    if (this.contents.isEmpty())
      return "()";
    String result = "(" + this.contents.get(last());
    for (int i = last()-1; i >= 0; i--)
      result = result + " " + this.contents.get(i);
    result = result + ")";
    return result;
  } // toString()

} // class VectorBasedStack