Is there any way to autofill custom fields without using a trigger while still using Apex code? I have fields that are aimed to be filled in based on more complex logic and accessing information of related list object information. I read something that I could make a VisualForce Page that will autopopulate the fields? In addition, the only use I know of for Apex Classes is calling them in Apex triggers. If there was a way for an Apex Class to initially fill in the fields based on my apex code, that would be ideal: I could run this class at any time I choose and my fields will be updated accordingly.
EDIT: for context, I have many contacts ALL of which I want to batch update certain fields. I do not want to use a trigger as that will only update the object associated with the insertion/update the trigger was fired upon. I want to use my code as a way to mass populate all objects fields based on some more advanced logic.
Any suggestions will help greatly.