I don't quite understand what you are saying here. First of all, (a-b)+c
is not at all the same expression as a-(b+c), and (a/b)*c is not the
same as a/(b*c). Addition and subtraction are different operations,
although they have equal precedence in Java.
Even ignoring that issue, for integer types multiplication and division
are non-associative, and for floating point types none of
multiplication, division, addition, and subtraction is associative. The
fact that Java evaluates a+b+c as (a+b)+c not a+(b+c) really does matter.