I have created a Java package, Matrix. When I attempt to run it, I get the error "Selection does not contain a main type". But, as the code that I've copied and pasted from the class DriverMatrix shows, there is a main method declaration. I have attempted to restart Eclipse and I still get the error. I created the package called Matrix, then imported .java files for each class. Anyone know what's going on here? Here is the main declaration along with just a bit of code: 

```
package Matrix;

import java.io.*;
import java.util.Scanner;

public class DriverMatrix 
{

static private IntegerArithmetics integerArithmetics = new IntegerArithmetics();
static private DoubleArithmetics doubleArithmetics = new DoubleArithmetics();

public static void main(String[] args) throws FileNotFoundException
{
    Scanner inFile = new Scanner (new FileReader("in.txt"));
    PrintWriter outFile = new PrintWriter("out.txt");

    Matrix<Integer,IntegerArithmetics> matrix1 = new Matrix<Integer,IntegerArithmetics>(integerArithmetics,2,3);
    Matrix<Integer,IntegerArithmetics> matrix2 = new Matrix<Integer,IntegerArithmetics>(integerArithmetics,2,3);
    Matrix<Integer,IntegerArithmetics> matrix3 = new Matrix<Integer,IntegerArithmetics>(integerArithmetics,2,3);
    Matrix<Integer,IntegerArithmetics> matrix4 = new Matrix<Integer,IntegerArithmetics>(integerArithmetics,2,3);
    Matrix<Integer,IntegerArithmetics> matrix5 = new Matrix<Integer,IntegerArithmetics>(integerArithmetics,3,2);
    Matrix<Integer,IntegerArithmetics> matrix6 = new Matrix<Integer,IntegerArithmetics>(integerArithmetics,2,2);

```