I can not figure out why am i getting the result 2

Question

Maybe I'm missing out but I can't figure out why I am getting the result 2 in this code:

i = 1;
i = i-- - --i;
System.out.println(i);

I have seen this in some java question. But in real live it is strongly very-very bad practice to do so. It is much better to write more simplier to be understandable for everyone. — Oleg Cherednik, Sep 13 '17 at 13:15
Why wouldn't you? You *are* decrementing `i` twice. And you shouldn't ever do this. — dhke, Sep 13 '17 at 13:15
I am expecting the number one. --i = 0 so 1 - 0 will be one. — Antonio, Sep 13 '17 at 13:16
@Antonio Java strictly evaluates left to right, so no, `--i` is `-1`, because `i--` already happened first. — dhke, Sep 13 '17 at 13:17
https://stackoverflow.com/questions/19216118/how-is-that-x-20x-x-x-x-final-value-of-x-in-java-is-65 — Suraj Rao, Sep 13 '17 at 13:17
I'm voting to close this question as off-topic because no one should write code like this. — duffymo, Sep 14 '17 at 01:02

score 3 · Accepted Answer · answered Sep 13 '17 at 13:15

3

In i = i-- - --i you have:

i--, a post-decrement, which retrieves the current value of i (1) and then decrements i to 0
-
--i, a pre-decrement, which decrements i again and retrieves the updated value, -1

So you end up with i = 1 - -1 which is 2.

Needless to say, this sort of thing shows up on (silly) Java tests and such, but should never appear in production code.

answered Sep 13 '17 at 13:15

T.J. Crowder

I can't believe I didn't catch this, thank you for the help. – Antonio Sep 13 '17 at 13:27

1 Answers1