The condition should hold at the end of every constructor.
The condition should hold at the end of every mutator(non-const) operation.

i have done  mba. and i have got 1 year of experience in marketing field. hence i have been asked the question. how could i answer it perfectly and impressively?

I think the question is little misspelled....I had to fire many people during company merger.. I had to do it..according to company policy..but I ensured that the fired employees got good severence pay..and they enjoyed being fired becos of the package and benefits they received :-)
I fired becos i had to fire due to company financial losses...
I know of companies who fire for silly and stupid reasons..

using SFLRCDNBR we can retrive RRN through rpg

Using *PSSR routine.
Declare a *PSSR rouine as a subroutine and write the code u need to handle the error.

copyfile command copies the contents of existing database file into another datbase file .
using cpyf -> we cancopy data from external device to a datbase file and viceversa.
crtdupobj-> create duplicate object, create clone exactly as the source file with structure and content with its link to prgram and logical file and its authority setting as well. no need to recompile pgm that use this file.

Data areas are objects of type DTAARA that we can create and delete at will..A data area that can be used to store informations with a name,but without any structure.
Dataqueues are permanent objects(type DTAQ) that can be used for asynchronously communicating a
strem of values between programs or jobs.