Assuming
boolean a = false;
I was wondering if doing:
a &= b;
is equivalent to
a = a && b; //logical AND, a is false hence b is not evaluated.
or on the other hand it means
a = a & b; //Bitwise AND. Both a and b are evaluated.
From the Java Language Specification - 15.26.2 Compound Assignment Operators.
A compound assignment expression of the form
E1 op= E2
is equivalent toE1 = (T)((E1) op (E2))
, whereT
is the type ofE1
, except thatE1
is evaluated only once.
So a &= b;
is equivalent to a = a & b;
.
(In some usages, the type-casting makes a difference to the result, but in this one b
has to be boolean
and the type-cast does nothing.)
And, for the record, a &&= b;
is not valid Java. There is no &&=
operator.
In practice, there is little semantic difference between a = a & b;
and a = a && b;
. (If b
is a variable or a constant, the result is going to be the same for both versions. There is only a semantic difference when b
is a subexpression that has side-effects. In the &
case, the side-effect always occurs. In the &&
case it occurs depending on the value of a
.)
On the performance side, the trade-off is between the cost of evaluating b
, and the cost of a test and branch of the value of a
, and the potential saving of avoiding an unnecessary assignment to a
. The analysis is not straight-forward, but unless the cost of calculating b
is non-trivial, the performance difference between the two versions is too small to be worth considering.