import java.util.Arrays;
import java.util.List;

/**
 *
 * @author Peter Cappello
 */
public class Summer
{    
    static double sum( List< ? extends Number> numberList )
    {   
        double sum = 0.0;
        for ( Number number : numberList )
        {
            sum += number.doubleValue(); // class Number has a doubleValue method.
        }
        return sum;
    }
    
    public static void main( String[] args )
    {
        Number[] numberArray = { 0.0, Math.PI, 7, new Float( -5 ) };
        List<Number> numberList = Arrays.asList( numberArray );
        for ( Number number : numberList )
        {
            System.out.println( "" + number );
        }
        System.out.println("Total: " + sum( numberList ) );
    }
}