A modified implementation of the DataSet class to use both a Measurer and a Filter object.

BankAccount.java

//BankAccount.java - Jimmy Kurian

public class BankAccount
{
   private double balance;

   public BankAccount()
   {
      balance = 0;
   }

   public BankAccount(double initialBalance)
   {
      balance = initialBalance;
   }

   public void deposit(double amount)
   {
      double newBalance = balance + amount;
      balance = newBalance;
   }

   public void withdraw(double amount)
   {
      double newBalance = balance - amount;
      balance = newBalance;
   }

   public double getBalance()
   {
      return balance;
   }
}

DataSet.java

//DataSet.java - Jimmy Kurian

public class DataSet
{
   private double sum;
   private Object maximum;
   private int count;
   private Measurer measurer;
   private Filter filter;

   public DataSet(Measurer aMeasurer, Filter aFilter)
   {
      sum = 0;
      count = 0;
      maximum = null;
      measurer = aMeasurer;
      filter = aFilter;
   }

   public void add(Object x)
   {
      if (filter.accept(x))
      {
         sum = sum + measurer.measure(x);
         if (count == 0
            || measurer.measure(maximum) < measurer.measure(x))
            maximum = x;
         count++;
      }
   }

   public double getAverage()
   {
      if (count == 0) return 0;
      else return sum / count;
   }

   public Object getMaximum()
   {
      return maximum;
   }
}

Filter.java

//Filter.java - Jimmy Kurian

public interface Filter
{
   boolean accept(Object x);
}

Measurer.java

//Measurer.java - Jimmy Kurian

public interface Measurer
{
   double measure(Object anObject);
}

MeasurerFilterTester.java

//MeasurerFilterTester.java - Jimmy Kurian

public class MeasurerFilterTester
{
   public static void main(String[] args)
   {
      class BankMeasurer implements Measurer
      {
         public double measure(Object anObject)
         {
            BankAccount ba = (BankAccount) anObject;
            return ba.getBalance();
         }
      }

      class BankFilter implements Filter
      {
         public boolean accept(Object x)
         {
            BankAccount ba = (BankAccount) x;
            return ba.getBalance() > 1000;
         }
      }

      Measurer m = new BankMeasurer();
      Filter f = new BankFilter();
      DataSet data = new DataSet(m, f);

      data.add(new BankAccount(1));
      data.add(new BankAccount(100));
      data.add(new BankAccount(2000));
      data.add(new BankAccount(950));
      data.add(new BankAccount(5000));

      System.out.println("Average balance= " + data.getAverage());
      BankAccount b = (BankAccount) data.getMaximum();
      double balance = b.getBalance();
      System.out.println("Highest balance= " + balance);
   }
}