Listing -. Calculating Euler’s Number e

import java.math.BigDecimal;

import java.math.MathContext;

import java.math.RoundingMode;

import java.util.concurrent.Callable;

import java.util.concurrent.ExecutionException;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.Future;

public class CalculateE

{

    final static int LASTITER = ;

    public static void main(String[] args)

    {

    ExecutorService executor = Executors.newFixedThreadPool();

    Callable<BigDecimal> callable;

        callable = new Callable<BigDecimal>()

        {

            @Override

            public BigDecimal call()

            {

                MathContext mc = new MathContext(, RoundingMode.HALF_UP);

                BigDecimal result = BigDecimal.ZERO;

                for (int i = ; i <= LASTITER; i++)

                {

                    BigDecimal factorial =

                    factorial(new BigDecimal(i));

                    BigDecimal res = BigDecimal.ONE.divide(factorial,mc);

                    result = result.add(res);

                }

                return result;

            }

            public BigDecimal factorial(BigDecimal n)

            {

                if (n.equals(BigDecimal.ZERO))

                return BigDecimal.ONE;

                else

                return n.multiply(factorial(n.

                subtract(BigDecimal.ONE)));

            }

        };

        Future<BigDecimal> taskFuture = executor.submit(callable);

        try

        {

            while (!taskFuture.isDone())

            System.out.println("waiting");

            System.out.println(taskFuture.get());

        }

        catch(ExecutionException ee)

        {

            System.err.println("task threw an exception");

            System.err.println(ee);

        }

        catch(InterruptedException ie)

        {

            System.err.println("interrupted while waiting");

        }

         executor.shutdownNow();

        }

}