invalid objects compile when executed?

we have objects that have become invalid (still trying to figure out why) there is no problem compiling them manually, but, I thought that invalid procedures or functions compiled automagically when you executed them?

any procedure or function or whatever.. becomes invalid because u might have changed the structure of the base table or either dropped and recreated or revoked the privileges and again granted. or u might have used export/import. many reasons to make all these objects invalid.

it true if u have proper grants and base tables which r used in procedures or functions , the at the time of execution these objects become valid.

u can even try to do this view. create view in different schema. remove grants. check the status of view . again grant and select the data using view.