Sybex OCP 11 Programmer I. Chapter 4. Answer to review question 13

[Oksana Cherniavskaia]

Hello Jeanne and Scott, I have found a possible typo in answers for review question 13. Here answer states that three distinct numbers are printed, it is not true. Three numbers printed, two of them distinct.

B, E. The code compiles without issue and prints three distinct numbers at runtime,

Excerpt From: Boyarsky, Jeanne. “OCP Oracle Certified Professional Java SE 11 Programmer I Study Guide”.

[Mikalai Zaikin]

Hi Oksana !
Could you post more context?
Jeanne and Scott are members here, but might reply not quickly, and there are many other people on this forum who can help/confirm who have no the book.
If you share more context, you might get an confirmation faster.
Best regards,
MZ

[Oksana Cherniavskaia]

Well, it really not a question on the subject. This is a clear typo. The context is that in program 3 figures printed, but both of them the same. So there are no 3 distinct numbers. That is all.

[Jeanne Boyarsky]

Confirmed and added to the errata. We even list two correct answers for those two distinct numbers!

[R. Klee]

Hi,

I'm not sure if the explaination

"In the second loop, animals already starts out not less than or equal to 1, but since it is a
do/while loop, it executes at least once."

for the code snippet

do {} while (animals++ <= 1);

is intended as I would read it.

To me it sound as if in a similiar while-loop the animals++ in the boolean expression wouldn't be executed. But as it is a part of the boolean expression and not of the loop's (empty) body, it should be executed here, too.

[Jesse Silverman]

Welcome to the Ranch!
The it in question is the contents of the
{}

that is, the body of the loop.

In previous exchanges with the authors, which can be found here, there were a number of times that they acknowledged that some other wording could perhaps be slightly clearer but was simply too verbose.  This might be another of them.

The difference between a while() { } loop and a do { } while () loop is that THE BODY of a do { } while loop will always execute at least once.
The conditional expression in a while() loop will always be evaluated at least once if the execution ever reaches the line containing the while()

So the conditional expression in a do { } while() loop will always be evaluated at least once, unless the code in the { } calls System.exit() or throws an exception which is not caught within the loop body.  In those cases it will never be evaluated.
Or, if you are a goofball and do something like this:
jshell> do { System.out.println("ha ha ha!"); break;} while (1 < 10)
ha ha ha!

I tend to agree with the authors that being this verbose in the book would just take up too much space, it is fun at the end of a work day to discuss it tho.

[R. Klee]

"In the second loop, animals already starts out not less than or equal to 1, but since animals++ is part of the boolean expression, it is executed once."
wouldn't be more verbose and it would make clear that the execution of the loop's body isn't the point here.
I don't think it needs an full explaination, too, as it is already explained in the chapter.

[Jesse Silverman]

I think in that place they are drawing the essential distinction between the while loop and the do while loop.
In both cases (except the wacky ones I showed for fun) the boolean expression is always evaluated at least once, that is what they have in common.
The essential difference between the while and do while loops is that the body of do while always gets executed at least once for all cases, whereas zero executions of the body is a perfectly expected outcome of a while loop.

I will leave it to the authors to consider, it wouldn't make an errata but I believe they are taking a hard look at things that might be made clearer in the next book covering Java 17/829 exam.