Decrement operator precedence confusion

Question

Here is the snippet from a book:
int y = 5;
int result = y-- * 3 / --y;
System.out.println("y = " + y);
System.out.println("result = " + result);Assuming increment and decrement have highest precedence, I don't get the explanation:
Order of operations dictates that the multiplication is evaluated first(WHY???). The valueof y is 5, so 5 * 3 is 15. The multiplication is done, so the post - decrement occurs and y
becomes 4. Now the division is evaluated and y is pre - decremented to 3 before the division,
resulting in 15 / 3 , which is 5. The output of this code is:
y = 3
result = 5
Any comments would be appreciated.

Answer 1

AntShay wrote:
Oh, no!
There's something more I don't get :)
Why is 5 *** 3 takes place instead of 4 *** 3? Pre-decrement has higher precedence, hasn't it?
So, from my point of view this should work as follow (please correct me where I'm wrong):
int y = 5;
int result = y-- *** 3 / --y;
1) y-- gets evaluated (y=4 now)
2) --y gets evaluated (y=3)
3) 3 *** 3 = 9
4) 9/3 = 3I don't know if pre-dec has higher precedence than mult, but even if it does, that doesn't matter. That's not what precedence means. It doesn't mean you jump around and do those operations first. I just means "This is where the implied parentheses go." The only affect it has on order of evaluation is when you have to evaluate something inside the implied parens first to get an operand for the next operation.
3 + 4 * 5In the above, mult has higher precedence than add, so it's equivalent to
3 + (4 * 5)It doesn't mean "first do all multiplications, then all adds." It means the implied parens are as above.
So:
1. evaluate 3
2. evaluate the RH operand of +++
2.1 evaluate 4
2.2 valuate 5
2.3 multiply 4 *** 5 --> 20
3. evaluate 3 +++ 20
So we did the mult before the add because we had to in order to get the value of the RHS operand of the plus. Indirectly it's because mult has higher precedence, but that's just a consequence of the implied parens, and we still evaluated the 3 before doing the mult. We did NOT do "all mults first, then all adds."
Similarly, if it had been
2 + 3 + 4 * 5we would eval 2, then eval 3, then add, then eval the RHS of the second plus operator, which means we'd have to eval 4 *** 5. Note that we do NOT eval 4 *** 5 as the very first step before all adds.
Now, say pre-dec has higher precedence than mult. It may, it may not, I don't know and I don't care. It doesn't matter here, but let's say it does.
y-- * 3 / --yis the same as
(y--) * 3 / (--y)Operands are still evaluated L to R. We don't just jump around.
1. Evaluate y--
1.1 value of expression is 5
1.2 decrement y to 4
2. Evaluate 3.
3. Multiply #1 *** #2 --> 5 *** 3 = 15
4. Evaluate --y
4.1 decrement y
4.2 valueof expression is 3
5. evaluate #3 / #4 --> 15 / 3 = 5
Edited by: jverd on Feb 12, 2010 11:54 AM
Edited by: jverd on Feb 12, 2010 11:56 AM