radha gogia wrote:"final reference variables must be initialized before the constructor completes."
The answer is given in the above sentence.
As Matthew wrote, the x must be initialised either straight away, or latest within a constructor, because it can be initialised only once.
If you wouldn't initialise latest in a constructor, in theory by default constructor should initialise it to a null (which would be wrong, as you wouldn't be able to change value later on).
Sorry, i'm still sick, can't express my minds properly