The Java Language Specification, Third Edition

EXPRESSIONS Evaluate Left-Hand Operand First 15.7.1
It is recommended that code not rely crucially on this specification. Code is
usually clearer when each expression contains at most one side effect, as its
outermost operation, and when code does not depend on exactly which exception
arises as a consequence of the left-to-right evaluation of expressions.
15.7.1 Evaluate Left-Hand Operand First
The left-hand operand of a binary operator appears to be fully evaluated before
any part of the right-hand operand is evaluated. For example, if the left-hand operand
contains an assignment to a variable and the right-hand operand contains a
reference to that same variable, then the value produced by the reference will
reflect the fact that the assignment occurred first.
Thus:
class Test {
public static void main(String[] args) {
int i = 2;
int j = (i=3) * i;
System.out.println(j);
}
}
prints:
9
It is not permitted for it to print 6 instead of 9.
If the operator is a compound-assignment operator (§15.26.2), then evaluation
of the left-hand operand includes both remembering the variable that the left-hand
operand denotes and fetching and saving that variable’s value for use in the
implied combining operation. So, for example, the test program:
class Test {
public static void main(String[] args) {
int a = 9;
a += (a = 3); // first example
System.out.println(a);
int b = 9;
b = b + (b = 3); // second example
System.out.println(b);
}
}
prints:
12
12
because the two assignment statements both fetch and remember the value of the
left-hand operand, which is 9, before the right-hand operand of the addition is
DRAFT
415