What do you mean, "call a class"? You don't call a class, you call a method - specifically, you send a message to an object telling it to execute some method.
The suggestion above works for static methods, which do not depend on an instance of the class. For example, Math.pow(2,4) will produce the value 16. However, if the method is not static, then you need an instance of the class, and that instance probably needs some sort of state for the method call to be meaningful. (if the method does not depend on the instance's state, then there's no need for it to be an instance method, of course)