You will need to initiate the associated objects to that object with the associations. By calling the appropriate functions like:
AssociatedEntity assEntity = filterObject.getFilterObject_AssociatedEntity();
Assuming you have an initialized filter object which a Java action provides you by default.
You may then use the attributes from that associated entity. And if you already had everything in system memory this will be the same as a retrieve by association in a microflow, not causing any DB interaction.