Enthuware

ch is never initialized. How can 'x = ( ba[ch] = b );' compile? does an uninitialized character default to '0'?

static and instance variables are always initialized to their default values if you don't initialize them explicitly.
Local variables aka automatic variables (i.e. variables declared in a method) must be initialized explicitly before using them.

I thought it will not compile, because default value for character primitive is \u0000, so we would have something like that ba[\u0000]

Every character is actually just an integer value. So, \u0000 is just an integer value 0. So b[ch] is b[0] if ch is '\u0000'.