Question

I’ve got two validator classes. Let’s say: Car Validator and Wheel validator, and the second one is enclosed in first.

CarBodyValidator.validate(){
    WheelValidator.validate();
}

I have more validators in CarBodyValidator, f.e EngineValidator etc. validate() should only return true or false, and at one time I want to print as many mistakes as possible (if validation returns false for some class, I want to validate other classes if they are not dependent on each other).
Now, let’s say that Wheel validator returns a useful information, that I need in the CarBody validator. F.e if wheel diameter is too big then I need that info in car validator to validate something else.
How do I pass that information. I could create a field in Wheel validator, that stores the parameter, but accessing it like that:

carBodyValidator.validate(){
    wheelValidator.validate();
    if (WheelValidator.getSmomething() == somethingElse){
      ...
    }

}

seems wrong (I mean validator should only validate and not do anything else). Is this the correct way or I should do it different.

Answer 1

In situations like this I often rely on the observer pattern. Please note this is all pseudo code.

Create a ValidatorObserver interface.

public interface ValidatorObserver{
   public void notify(int errorKey);
}

Make CarBodyValidator implement this interface.

public class CarBodyValidator implements ValidatorObserver{

    public void notify(int errorKey){
       switch(errorKey){
         //Evaluate cases and do something.
       }
    }
}

Create a register method on WheelValidator and setup notification

public class WheelValidator{
    private List<ValdiatorObserver> observers = new ArrayList<ValidatorObserver>();

    public void addObserver(ValidatorObserver observer){
       observers.add(observer);
    }

    public void validate(){
       //if validation fails
       for(ValidationObserver observer: observers){
          observers.notify(1); //1 is an error code
       }
    }
}

Somewhere in your code you will need to register the observer

CarBodyValiator cbValidator = new CarBodyValidator();
WheelValidator wheelValidator = new WheelValidator();
wheelValidator.addObserver(cbValidator);