A modified version of the DataSet class that accepts Comparable objects.

DataSet.java

//DataSet.java - Jimmy Kurian

public class DataSet
{
   private Comparable minimum;
   private Comparable maximum;

   public DataSet()
   {
      maximum = null;
      minimum = null;
   }

   public void add(Comparable x)
   {
      if(minimum == null || x.compareTo(minimum) < 0)
         minimum = x;
      if(maximum == null || x.compareTo(maximum) > 0)
         maximum = x;
   }

   public Comparable getMaximum()
   {
      return maximum;
   }

   public Comparable getMinimum()
   {
      return minimum;
   }
}

DataSetTester.java

//DataSetTester.java - Jimmy Kurian

public class DataSetTester
{
   public static void main(String[] args)
   {
      DataSet data = new DataSet();

      data.add(new String("Jimmy"));
      data.add(new String("Anil"));
      data.add(new String("Melissa"));
      data.add(new String("Victor"));

      String max = (String) data.getMaximum();
      String min = (String) data.getMinimum();
      System.out.println("Maximum String = " + max);
      System.out.println("Minimum String = " + min);
    }
}

Thanks for the code. Really helpful. But i think, we can use default constructor without declaring max and min value.