generating a binary sequence

generating a binary sequence

I need to generate a binary sequence of keys where each key is of length
'x',and each key is generated by a specific operation on the previous key.
So assuming the key length to be 3,I should be able to generate a sequence
as(illustration):
001 010 100 011 .....
Each key has to be derived by some bit operation on the previous key,till
we have exhausted all possible permutations for that specific key length.
Since I am a newbie on bit operations - is this a possible operation;and
how do we generate this sequence for any given length.
I would prefer an example in java - but the idea is to understand the
logic and the specific oepration.