java - "Once-initialized" variables that are not initialized in construction time -

is there way in java create variables final not initialized inside constructor, yet once initialized can never changed again? problem variable values @ different time points , i'd create class before or receive first value.

i've thought obvious solution of keeping flag each variable, wanted know if there's more efficient that.

i along lines of last answer here. set fields setter, , if field not default value (i.e. null), not allow set.