package arrayPoly;

/**
 * Represents the polynomial abstraction.  Holds the coefficient.  Has two concrete
 * subclasses, ConstPoly and NonConstPoly, to form the composite pattern.  The client
 * should only know about APolynomial and nothing about its subclasses.  A factory,
 * PolyFactory, is used to manufacture polynomial objects for the client.
 * <pre>
 * Copyright 2000, by Dung X. Nguyen, All rights reserved.
 * </pre>
 * @author Dung X. Nguyen
 * @since 02/16/2000
 * @dependency arrayPoly.IVisitor uses
 */
public abstract class APolynomial
{
   /**
   * The leadin coefficient.
   */
	private double _coef;
	/**
	 * @return the leading coefficient of the referencing polynomial.
	 */
	public double getLeadCoef()
	{
      return _coef;
	}

	/**
	 * @return the degree (or order) of the referencing polynomial.
	 */
	public abstract int getDegree ();

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

	/**
    * Hook to perform all visitor polynomial algorithms.
	 * @param algo an algorithm on Polynomials.
	 * @param input the input needed by algo. 
	 * @param owner the context of this abstract polynomial type.
    * @return the output object for algo.
	 */
	public abstract Object execute(IVisitor algo, Object input);

   /**
   * Returns the String representation as the lowest order term in a higher order polynomial.
   * Helper for toString() method.
   */
   protected abstract String toString4LowerPoly ();
}