Rogerio,
In case of badis the field flt_val gets added automatically as an import parameter when you check FILTER DEPENDENT check box. This is to restrict which implementation of the badi should be executed, if there are more than one.
There is no such concept when you are building a class.
If you want one of your methods to be executed on in certain cases, you need add the required logic within the method.
If you are referring to the FILTER check box in the pic below, that is used for a different purpose. It is used to filter what is displayed on the class builder screen. F1 on the field to know more about the same.
Thanks,
Vikram.M