Java operands usage

Question

int a = 3;
int b = (a=2)*a;
int c = b * (b=5);
System.out.println("a=" + a + " b=" + b + " c=" + c);

Can someone explain me why the output is:

a=2 b=5 c=20

instead of

a=2 b=4 c=20

score 2 · Answer 1 · edited May 23 '17 at 11:50

Because assignment is an operator which returns the new value it set and, while it's normally last in precedence, the parentheses move it up before the non-parenthetical operators. Think of it like this:

a is set to 3.
a is set to 2, returning 2. That is then multiplied by the new value of a, which is 2, setting b to 4.
4 (old b) is multiplied by the result of b=5, which is 5. b is now 5, and c is set to the 4x5 value (20).

score 1 · Answer 2 · answered Nov 11 '13 at 15:44

1

You have reassigned b to a 5 in the second statement. As a result b will be 5 until it is assigned again. What part of this is confusing you?

answered Nov 11 '13 at 15:44

ford prefect

Oh now I get it. I forgot about the second assignment. Such a stupid question I've asked.. – jojuk Nov 11 '13 at 15:46

score 1 · Answer 3 · answered Nov 11 '13 at 15:44

1

You are assigning 5 to b, in the third line. So, that's what it contains.

answered Nov 11 '13 at 15:44

Darius X.

@Cruncher I don't think it's assignment as comparison just a misunderstanding of scope – ford prefect Nov 11 '13 at 15:46
@inquisitiveIdiot Oh, I didn't even look that close. I just saw `b=5` inside of an expression and sort of assumed – Cruncher Nov 11 '13 at 15:48

score 1 · Answer 4 · answered Nov 11 '13 at 15:47

1

b is 5 because of this (b=5);

a is 2 because of this (a=2)

c is 20 because of this 4 * (b=5);

answered Nov 11 '13 at 15:47

4 Answers4