/**
 * Represents the polynomial abstraction.  Holds the coefficient.  Has two concrete
 * subclasses, ConstPoly and NonConstPoly, to form the composite pattern.
 * @author Dung X. Nguyen
 * @since 01/26/00
 */
public abstract class APolynomial
{
   /**
   * This APolynomial leading coefficient.
   */
	protected double _coef;

	/**
	 * Returns the leading coefficient of this APolynomial.
	 */
	public double getLeadCoef ()
	{
		return _coef;
	}

	/**
	 * Returns the degree (or order) of this APolynomial.
	 */
	public abstract int getDegree ();

   /**
   * Returns the lower ordered polynomial of this APolynomial, if any.
   * @exception throws NoSuchElementException if this APolynomial is a constant.
   */
	public abstract APolynomial getLowerPoly ();

	/**
   * Computes and returns the sum of this APolynomial with the parameter p.
   * @param p an APolynomial to be added to this APolynomial.
   * @return an APolynomial representing the sum of this APolynomial and the parameter p.
   */
	public abstract APolynomial add (APolynomial p);


	/**
   * Computes and returns the value of this APolynomial at a "point" x.
   * @param x the "point" at which this APolynomial is to be evaluated.
   * @return the value of this APolynomial evaluated at the parameter x.
   */
	public abstract double eval (double x);

   /**
   * Called by an APolynomial that contains this APolynomial as its lower order polynomial.
   * Relegates to concrete subclass to compute the appropriate String for the lower
   * order polynomial if any.  This is an example of we call a "helper" method for toString().
   */
   abstract String toString4LowerPoly ();

}