This is how you should do it
Code:
public class Test
{
	public static void main(String[] args) throws Exception
	{
		Class<?> c = Class.forName("TestPlayer");
		Object o = c.newInstance();
		String x = (String) c.getMethod("getUsername", (Class[]) null).invoke(o, (Object[])null);
		System.out.println(x);
	}
}