Creating an instance for a ball (with characteristics) to be used in a test harness

I'm trying to create an instance named Ball with certain characteristics that will be tested in a test harness, such as radius, location, and initialVelocity. I keep getting errors from the instance lines however. This is what i have so far. Note: This is already in a public class, but this is just a snippet of the complete code.

private static void test_ball() {
      Ball a = new Ball(4,8);
      radius = a.getRadius(10);
      location = a.getLocation(4,8);
      initialVelocity = a.initialVelocity(20,15);
        System.out.println("Testing ball getlocation method...");
        try {
            displaySuccessIfTrue(ball.getLocation(a.x() == 4 && a.y() == 8));
        } catch(Exception e) {
            displaySuccessIfTrue(false);
        }
        System.out.println("Testing ball getRadius method...");
        try {
            displaySuccessIfTrue(a.getRadius() == 10);
        } catch(Exception e) {
            displaySuccessIfTrue(false);
        }
        System.out.println("Testing ball initialVelocity method...");
        try {
            displaySuccessIfTrue(ball.initialVelocity(a.initialVelocity.x() == 20 && a.initialVelocity.y() == 15);
        } catch(Exception e) {
            displaySuccessIfTrue(false);
        }
}**