import java.beans.*;

/** 
 *  The Aveage class finds and keeps track of the average
 *  of an array of Doubles.
 *
 *  @author Stuart Hansen
 *  @version September 2008
 */
public class Average
{   
   // We maintain the average in order to have an old
   // average for the property change event
   private Double average;

   // We use pcs to facilitate our property change events
   private PropertyChangeSupport pcs;

   // The default constructor
   public Average()
   {
      average = new Double (Double.NaN);
      pcs = new PropertyChangeSupport (this);
   }

   // Return the current Average
   public Double getAverage()
   {
      return average;
   }

   // Return the current Average as a String
   public String toString ()
   {
      return average.toString();
   }

   // Find the average of an enumeration of Doubles
   public Double findAverage(Double[] dArr)
   {
      Double oldAverage = average;
      
      if (dArr.length > 0)
      {
         double sum = 0.0;
         int count = 0;
         for (Double d : dArr) {
            sum += d;
            count++;
         }
         average = new Double (sum/count);
      }
      else
         average = Double.NaN;
      
      firePropertyChange (new PropertyChangeEvent (this, "average", 
                     oldAverage, average));
      return average;
   }

   // Fire a property change
   public void firePropertyChange (PropertyChangeEvent e)
   {
      pcs.firePropertyChange(e);
   }

   // Add a property change listener
   public void addPropertyChangeListener(PropertyChangeListener pcl)
   {
      pcs.addPropertyChangeListener(pcl);
   }

   // Delete a property change listener
   public void removePropertyChangeListener(PropertyChangeListener pcl)
   {
      pcs.removePropertyChangeListener(pcl);
   }
}