/**
 *
 */
package de.fhswf.in.inf.upnfx.util;


/**
 * An abstract class for calculations with unary operators.
 *
 * @author $Author: $
 * @version $Revision: $, $Date: $ UTC
 */
public abstract class UnaryOperator implements Operator
{
   /*
    * (non-Javadoc)
    *
    * @see de.fhswf.in.inf.java1.aufgabe12.Operator#eval(java.util.Stack)
    */
   @Override
   public final void eval(ObservableDoubleStack stack)
   {
      if (stack == null)
      {
         throw new IllegalArgumentException("Stack must not be null.");
      }

      if (stack.size() < 1)
      {
         throw new IllegalArgumentException(
               "Unary operation requires one operand.");
      }

      double d = stack.pop();

      stack.push(eval(d));
   }

   /**
    * This class implements the calculation.
    *
    * @param d
    *           The unary operator.
    * @return The result of the calculation.
    */
   abstract double eval(double d);
}