OOP Design Question - Validating properties

Question

I have the habit of always validating property setters against bad data, even if there's no where in my program that would reasonably input bad data. My QA person doesn't want me throwing exceptions unless I can explain where they would occur. Should I be validating all properties? Is there a standard on this I could point to?

Example:

public void setName(String newName){
   if (newName == null){
      throw new IllegalArgumentException("Name cannot be null");
   }
   name = newName;
}

...

//Only call to setName(String)
t.setName("Jim");

Answer 1

You're enforcing your method's preconditions, which are an important part of its contract. There's nothing wrong with doing that, and it also serves as self-documenting code (if I read your method's code, I immediately see what I shouldn't pass to it), though asserts may be preferable for that.

Answer 2

Personally I prefer using Asserts in these wildly improbable cases just to avoid difficult to read code but to make it clear that assumptions are being made in the function's algorithms.

But, of course, this is very much a judgement call that has to be made on a case-by-case basis. You can see it (and I have seen it) get completely out of hand - to the point where a simple function is turned into a tangle of if statements that pretty much never evaluate to true.