Java Executor Service

import java.util.ArrayList;
import java.util.List;
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 ParallelClass {

    public static class PrimeResult {
        private final long number;
        private final boolean isPrime;
        public PrimeResult (long number, boolean isPrime) {
            this.number = number;
            this.isPrime = isPrime;
        }
    }


    // Method used to check if a number is a prime number
    public static PrimeResult CheckIfPrime(long n) throws InterruptedException
    {
        long i;
        for (i = 2; i <= n - 1; i++)
        {
            if (n % i == 0)
            {
                return new PrimeResult(n, false);
            }
        }

        return new PrimeResult(n, true);
    }

    public static void main(String[] args) {

        long first = 0;
        long last  = 1_000_000;
        int availableProcessors = Runtime.getRuntime().availableProcessors();

        System.out.println("Available processors: " + availableProcessors);
        System.out.println("Starting check from " + first + " to " + last + "...");

        // Create a list of tasks to execute
        List<Callable<PrimeResult>> tasks = new ArrayList<Callable<PrimeResult>>();
        for (long i = first; i < last; i++) {

            final long iter = i;
            Callable<PrimeResult> c = new Callable<PrimeResult>() {
                @Override
                public PrimeResult call() throws Exception {
                    return CheckIfPrime(iter);
                }
            };
            tasks.add(c);
        }

        // Create the Executor Service
        ExecutorService exec = Executors.newFixedThreadPool(availableProcessors);
        //ExecutorService exec = Executors.newSingleThreadExecutor();
        try {
            long start = System.currentTimeMillis();
            List<Future<PrimeResult>> results = exec.invokeAll(tasks);
            for (Future<PrimeResult> fpr : results) {
                System.out.println("Number " + fpr.get().number + " is prime? " + fpr.get().isPrime);
            }
            long elapsed = System.currentTimeMillis() - start;
            System.out.println(String.format("Elapsed time: %d ms", elapsed));
        } catch (Exception ex) {
            System.out.println("An exception occurred! Exception message:");
            System.out.println(ex.getMessage());
        }
        finally {
            exec.shutdown();
        }

        System.out.println("Finished!");
    }

}