Question

I wonder, what is the best practice for object validation. Is there any extra argument against case one or case two? Is there another way?

I don’t search for any validation library, I just want to do simple validation.

Case One

class A {
   public void doSomething(MyObject o) {
      try {
         validate(o);
         doSomethingUseful(o);
      } catch (ValidationException e) {
         Logger.getLogger().warn(e);
      }
   }

   private void validate(MyObject o) throws ValidationException
   { 
      if (o.getXYZ() == null) 
         throw new ValidationException("Field XYZ cannot be null");
   }

   private void doSomethingUseful(MyObject o) { //some funny stuff }
}

Case Two

class A {
   public void doSomething(MyObject o) {
      if (validate(o)) {
         doSomethingUseful(o);
      } else
         Logger.getLogger().warn("Object is invalid");
      }
   }

   private boolean validate(MyObject o)
   { 
      if (o.getXYZ() == null) return false;
      return true;
   }

   private void doSomethingUseful(MyObject o) { //some funny stuff }
}

Answer 1

If you are just swallowing the exception and if the validation method is only private, then prefer case two since you should not use exceptions for normal logic.

If you want to let the client handle the exception, which you should, then use case one but let it throw instead of swallowing.