Pre- and postincrement in Java

I just wanted to create a little Java-Puzzle, but I puzzled myself. One part of the puzzle is: What does the following piece of code do: ``` public class test { public static void main(String[] args) { int i = 1; i += ++i + i++ + ++i; System.out.println("i = " + i); } } ``` It outputs `9`. My (at least partly) wrong explanation: I'm not quite sure, but I think the term after `i +=` gets evaluated like this: So ``` int i = 1; i += ++i + i++ + ++i; ``` is the same as ``` int i = 1; i += ((++i) + (i++)) + (++i); ``` This gets evaluated from left to right (See Pre and postincrement java evaluation). The first `++i` increments `i` to `2` and returns `2`. So you have: ``` i = 2; i += (2 + (i++)) + (++i); ``` The `i++` returns `2`, as it is the new value of `i`, and increments `i` to `3`: ``` i = 3; i += (2 + 2) + ++i; ``` The second `++i` increments `i` to `4` and returns `4`: ``` i = 4; i += (2 + 2) + 4; ``` So you end up with `12`, not `9`. Where is the error in my explanation? What would be a correct explanation?