Learning Java - Chapter 4 : Tech

Here we make a subclass of the BasicHist class discussed in Chapter 3: Tech : Histograms. The class definition below shows that BetterHist inherits BasicHist, obtaining the properties of the latter while providing new capabilities.

Note how the constructor invokes super() to select a constructor in the base class.Also, we see how the new methods in the subclass can access the data variables in the bass class (In the next chapter we will discuss access modifers such as private, which prevents subclasses from accessing a class property.)

We add several methods to our histogram that provide various values describing the histogram. Also, a calculation of the mean and standard deviation of the distribution in the histogram is made.

BetterHist.java

/** This histogram class extends BasicHist to add more
  * capabilities. **/
public class BetterHist extends BasicHist
{
   /** This constructor initializes the basic elements of
     * the histogram.
    **/
   public BetterHist (int numBins, double lo, double hi)  {
      supper (numBins, lo, hi);
   }

   /** Get the low end of the range. **/
   public int getLo () {
     return lo;
   }

   /** Get the high end of the range. **/
   public int getHi () {
     return hi;
   }

   /** Get the number of entries in the largest bin. **/
   public int getMax () {
     int max = 0;
     for (int i=0; i < numBins;i++)
          if( max < bins[i]) max = bins[i];
     return max;
   }

   /** Get the number of entries in the smallest bin. **/
   public int getMin () {
     int min = getMax;
     for (int i=0; i < numBins;i++)
          if( min > bins[i]) min = bins[i];
     return min;
   }

   /** Get the total number of entries. **/
   public int getTotal() {
     int min = 0;
     for (int i=0; i < numBins; i++)
          if (min > bins[i]) min = bins[i];
     return min;
   }

  /** Get the average and std dev of the distribution **/
   public double [] getStats ()
   {
     int total = 0;

     double wtTotal = 0;
     double wtTotal2 = 0;
     double [] stat = new double[2];
     double binWidth = range/numBins;

     for (int i=0; i < numBins;i++) {
       total += bins[i];

       double binMid = (i - 0.5) * binWidth + lo;
       wtTotal += bins[i] * binMid;
       wtTotal2 += bins[i] * binMid * binMid;
     }

     if (total > 0)  {
        stat[0] = wtTotal/total;
        double av2 = wtTotal2/total;
        stat[1] = Math.sqrt (av2 - stat[0] * stat[0]);
     }else {
        stat[0] = 0.0;
        stat[1] = -1.0;
     }

     return stat;
   } // get Stats
} // class BetterHist