Reset for validation
There is a reset() method on ActionForm that is called *before* Struts does the auto-populate trick. The contract is that this method should reset all relevant attributes for this particular form to default values. For checkboxes, you would want to set the corresponding boolean to false. It will be set to true by the auto-populate method *if and only if* the checkbox was checked (and therefore included in the POST).
For integers, it is technically feasible to distinguish an empty field ("") versus a zero ("0"). If we decide not to call the setter in this scenario, then the ActionForm property will remain at it's default value, so you can distinguish whether it was entered or not.