Sybex OCP11-Complete - Chapter-3 - Increment and Decrement Operators - Lion and Tiger - Kindle

[Frank Mi]

Hi,

I created a new post because this is on a different book, the complete version. I'm new here and not familiar with the regulation. If this is not allowed, I will delete it.

This problem has been discussed in another post, and according to Campbell Ritchie's reply and tests, the 1z0-815 version, which reads "First, lion is incremented", is correct.

Campbell Ritchie wrote:Yes, as we concluded earlier, the original explanation in the book appears to be correct.

That is to say, in code

int tiger = ++lion *  5 / lion--;

++lion should be evaluated before lion-- because of order of evaluation.

However, it looks like the author misunderstood Campbell Ritchie and put it into errata again.

Jeanne Boyarsky wrote:And back to errata.

And now, it is still in the errata of 1z0-815, and to the contrary, the complete study guide reads "First, lion is decremented."

I can tell, only one of the two versions is correct, right? In my own opinion, the original one is correct.

[Campbell Ritchie]

Welcome to the Ranch

Not got the time or energy to go through this problem in detail, but it appears from the older discussion you quoted that the older versions of the book had the correct explanation but not the later edition. I think my example starting −1 shows that the ++ is executed first. If the -- were executed first, the code wouldn't throw an exception.

[Frank Mi]

Thanks. ^_^

Yes, long story short, the 1z0-815 book might be correct (the same as what you said), but it was put into errata incorrectly, then affect the new complete version.

[Campbell Ritchie]

Again to cut a long story short, whichever version says ++ is executed first is correct.

[Frank Mi]

Got it, thanks. I don't know how to @ person in this forum, could you tell me how to inform the authors to put it onto errata?

[Campbell Ritchie]

Please wait; one of the authors checks this forum regularly.

[Jeanne Boyarsky]

I've added it back to the errata. Scott and I discussed it and we want to get rid of this example. it's too complicated for the exam. It's also too complicated to explain/understand to be useful.

[Frank Mi]

Hi Jeanne and Scott,

Thank you for your reply. Though I don't agree that it is too complicated, actually it is common and in scope of the exam. So please modify but don't get rid of the example.

According to JLS §15.7.1:

JLS §15.7.1 wrote:The left-hand operand of a binary operator appears to be fully evaluated before any part of the right-hand operand is evaluated.

So that,

int tiger = ++lion * 5 / lion--;

is the same as:

int tiger = ((++lion) * 5) / lion--;

Other than that, I've seen several java mock exam questions like the following one:

int x1 = 10;
int y1 = x1++ - ++x1; // y1 = ((x1++) - ++x) = 10 - 12 = -2

int x2 = 10;
int y2 = ++x2 - x2++; // y2 = ((++x2) - x2++) = 11 - 11 = 0

These questions are fine and should be understood by us.

Do you think what I said make sense?

[Jeanne Boyarsky]

Frank,
The number of people who found it confusing suggests it isn't furthering our goals here . I'm glad you understand it though!

[Frank Mi]

Hi Jeanne,

Sorry for bothering you again. But the information in the Errata (both the 1z0-815 and the complete version) is still incorrect. It should be "++lion should execute before lion–",  rather than after.

[Jeanne Boyarsky]

Frank Mi wrote:Hi Jeanne,

Sorry for bothering you again. But the information in the Errata (both the 1z0-815 and the complete version) is still incorrect. It should be "++lion should execute before lion–",  rather than after.

Yup. Thank you

[Cristian Sanchez]

I was reading the edition published in Oreily, I believe the example is a pretty good one, but maybe you can use other numbers in order to avoid that as readers we misunderstand the example.

In the book, we can see

int tiger = 3 * 5 / 3;

Which unfortunately has the same result as the following

int tiger = 4 * 5 / 4;

And that result is (at least from my point of view) the one that got me confused.

After changing the value of the lion's variable to a different number is easier to understand how the operators are changing the lion variable.