My boxers are not good with cats at all, but we have outdoor cats. Samson, if he catches one, will lick it until it appears to have had a shower. He has never hurt one. Delilah, I will not go into details, cannot be trusted with a cat at all. I do believe; however, if we had indoor cats and if the boxers were exposed to them all of the time, it would be a much calmer situation.
I agree with everyone, it depends upon the boxer.