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++ operator

Robbie kyodo
Ranch Hand

Joined: May 05, 2003
Posts: 97
int y = ++x + x++;
if x = 2
can somebody explain ?


SCJP 2 1.4
Yi Meng
Ranch Hand

Joined: May 07, 2003
Posts: 270
Originally posted by Robbie kyodo:
int y = ++x + x++;
if x = 2

y=6
++x: increase x by 1 and then evaluate x, so this expression will be of vaule 3 and x is also 3
x++: (remember x is 3 already by ++x!)evaluate x and then increase x by 1. so the expression will be of value 3 and x will be 4.
acording the above explanation, both expressions are of value 3 and thus y=3+3=6....
you may try:


what's x?


Meng Yi
Robbie kyodo
Ranch Hand

Joined: May 05, 2003
Posts: 97
int x=2; x += ++x + x++;
x = 2 + 3 + 3
8 ? is it right ?
Anupam Sinha
Ranch Hand

Joined: Apr 13, 2003
Posts: 1088
Hi Robbie
In java intial evaluation order is left to right. So now evaluate ++x + x++ which gives us 3 + 3; but now makes x = 4. when first ++x is encountered it gives 3 then the value of x which is now three is now put in x, so now x also gets three, now x is incremented and now x will contain 4. So y will be 3+3=6. The evaluation order for = is right to left.
int x=2; x += ++x + x++;
x = 2 + 3 + 3
8 ? is it right ?

Right.
[ May 26, 2003: Message edited by: Anupam Sinha ]
Yi Meng
Ranch Hand

Joined: May 07, 2003
Posts: 270
Yi Meng
Ranch Hand

Joined: May 07, 2003
Posts: 270
8 is correct.
there is no such an operator =+. To me it is just the same as = .
Jessica Sant
Sheriff

Joined: Oct 17, 2001
Posts: 4313

Realize that order of operations and precedence isn't tested on the SCPJ exam. So I'd recommend concentrating more on inner classes and threads and fun stuff like that. In real life you'll use lots of ( )'s to make the precedence in your arithmatic to make things clear.


- Jess
Blog:KnitClimbJava | Twitter: jsant | Ravelry: wingedsheep
Jessica Sant
Sheriff

Joined: Oct 17, 2001
Posts: 4313

Robbie-
I goofed. I was editing / deleting a post of mine in this thread, and I think the UBB got a little mixed up and it accidently deleted YOUR post instead of mine. My apologies!!
- Jess
Robbie kyodo
Ranch Hand

Joined: May 05, 2003
Posts: 97
I repost my message again

I think I mistype
x =+ ++x + x++
instead of += I typed =+
it still compiles. why ?
Yi Meng
Ranch Hand

Joined: May 07, 2003
Posts: 270
Originally posted by Robbie kyodo:
I repost my message again

I think I mistype
x =+ ++x + x++
instead of += I typed =+
it still compiles. why ?

I think for =+, it is not a compound operator, but rather a combination of operators.
form maths, we know that +5 is positive five and is equal to 5 and +(-5) is still -5.
so op1=+op2 is just the same as op1=op2, op1 and op2 are compatible numeric values here.
something strange as y=+-5; is by all means valid in java. it is just the same as y= + (-5); and further more the same as y=-5;
hope it helps.........(help myself as well )
[ May 27, 2003: Message edited by: Yi Meng ]
 
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