Errata OCP 17 Developer Study Guide

[Stefan Banu]

Hi everyone,

don't know exactly where to post this:

on chapter 2 on "Complement and Negation Operators" there are this lines:

zooTemperature = -(-zooTemperature);
System.out.println(zooTemperature); // -1.21

but the actual result should be 1.21 and not  -1.21

I know it's a small thing but I think is good to be corrected.

thank you,
Stefan Banu

[Marco Olivi]

Hi Stefan!
The full code is:

double zooTemperature = 1.21;
System.out.println(zooTemperature);  // 1.21
zooTemperature = -zooTemperature;
System.out.println(zooTemperature);  // -1.21
zooTemperature = -(-zooTemperature);
System.out.println(zooTemperature);  // -1.21

On the third line the variable zooTemperature is reassigned to -1.21, as printed on line 4. The fifth line then reassign the variable again, with a double negation. So the result is stil -1.21

[Jeanne Boyarsky]

I ran it again and confirmed I got what Marco (and the book) got.

[Stefan Banu]

Yes, thank you,
my bad.

[Guillaume Bailly]

Hi,

In the introduction on page xxxiii there is a small typo in my opinion.

"The review questions in each chapter are designed to help you home in..."

should be "...hone in..."

I'm not a native speaker, so my apologies if this was correct and I got it wrong.

Kind regards,
Guillaume

[Guillaume Bailly]

Hi,

Still in the introduction, on page lx, I am wondering about the accuracy of the following statement:

"14. D, E. Line 10 includes an unhandled checked IOException..."

Actually, exactly at line 10 there is nothing wrong according to the Javadoc for BufferedInputStream.
But I have to admit, a lot is going wrong in this excerpt code.
And in the end, it is up to the reader to verify this for a better understanding for the exam.

Kind regards,
Guillaume

[Marco Olivi]

The IOException to be handled is actually on line 11, when a new FileInputStream is created.

[Jeanne Boyarsky]

Guillaume Bailly wrote:Hi,

In the introduction on page xxxiii there is a small typo in my opinion.

"The review questions in each chapter are designed to help you home in..."

should be "...hone in..."

I'm not a native speaker, so my apologies if this was correct and I got it wrong.

Kind regards,
Guillaume

You are correct. I added it to the errata. Interestingly, it was right in the Java 11 book. And this isn't a part we change so an editor must have misread.

[Jeanne Boyarsky]

Marco Olivi wrote:The IOException to be handled is actually on line 11, when a new FileInputStream is created.

Agreed. Gave Guillaume the errata credit for finding it and Marco a cow for noting the correction. Thanks to you both!

[Guillaume Bailly]

Hi,

Since I'm not sure where to put this, I will continue here.

Although the rules for identifiers on page 35 are clear, the rationale on page 36 in the examples could be more precise.

In particular, instead of
 "@ is not a letter, digit, $ or _"
I would suggest
 "@ is not a letter, digit, currency symbol or _"

The next one is even a bit wrong according to the rules.

Instead of
 "* is not a letter, digit, $ or _"
I would suggest
 "* is not a letter, currency symbol or _"
(digit would not be allowed here)

Guillaume

[Guillaume Bailly]

Hi,

About that last one, I would also propose a similar correction for answer to review question 4 of chapter 1 (page 910).

It would be more accurate in my opinion to say "currency symbol" instead of "dollar sign".

Guillaume

[Jeanne Boyarsky]

We actually had currency symbol in our Java 11 book and a reader noticed this was wrong. The following is from the Java Language Specification. The word "currency" doesn't appear in the JLS so we decide to go with $ in the Java 17 book.

It makes no practical effect for the exam. They won't show you an identifier with a euro character or the like.

A "Java letter" is a character for which the method Character.isJavaIdentifierStart(int) returns true.

A "Java letter-or-digit" is a character for which the method Character.isJavaIdentifierPart(int) returns true.

The "Java letters" include uppercase and lowercase ASCII Latin letters A-Z (\u0041-\u005a), and a-z (\u0061-\u007a), and, for historical reasons, the ASCII underscore (_, or \u005f) and dollar sign ($, or \u0024). The $ sign should be used only in mechanically generated source code or, rarely, to access pre-existing names on legacy systems.

[Guillaume Bailly]

Hi,

On page 183, right before the section "Sorting", one can read

"...which is also a way of referring to that tenth element."

to refer to the element at index 10.

What one actually means then is "the eleventh element" (which does not exist).

Guillaume

[Jeanne Boyarsky]

Confirmed and added to the errata

[Guillaume Bailly]

Hi,

The following is a tiny one in the text and is more for completeness.

In the correction of question 19 for chapter 4 review questions on page 923, I would rather say something like

"This is the case for option A since the element at index 1 of s2 comes first alphabetically."

This makes it clearer in my opinion.

Kind regards.

[Guillaume Bailly]

Hi,

At the top of page 364, the enum value that is mentioned is Season.FALL, while the code (at the bottom of page 363) actually uses Season.WINTER.

Guillaume

[Fernando László Temesi Villagrán]

Hello, all.

I found 2 possible erratas on book OCP Oracle Certified Professional Java SE 17 Developer Study Guide: Exam 1Z0-829.

1) On page 443, in the

compose()

example the result should be 7 and not 8 on line

System.out.println(combined.apply(3)); // 8

.

2) In Table 9.6, (page 485) it says

public V merge(K key, V value, Function(<V, V, V> func))

. It should be

public (default?) V merge(K key, V value, BiFunction<V, V, V> func)

.

Where could I find the whole erratas table for this book?

Kind regards.

László.

[Paul Clapham]

Jeanne Boyarsky wrote:

Guillaume Bailly wrote:Hi,

In the introduction on page xxxiii there is a small typo in my opinion.

"The review questions in each chapter are designed to help you home in..."

should be "...hone in..."

I'm not a native speaker, so my apologies if this was correct and I got it wrong.

Kind regards,
Guillaume

You are correct. I added it to the errata. Interestingly, it was right in the Java 11 book. And this isn't a part we change so an editor must have misread.

Old people would use "home in" because that used to be the standard usage. Recently people have started using "hone in" instead. So there's sort of a controversy. You might want to choose a different phrase.

Merriam-Webster

[Guillaume Bailly]

Hi,

Good to know Paul, thanks!

Kind regards,
Guillaume

[Jeanne Boyarsky]

Fernando László Temesi Villagrán wrote:1) On page 443, in the

compose()

example the result should be 7 and not 8 on line

System.out.println(combined.apply(3)); // 8

.

I ran it again and still get 8. Which matches the book. Remember that with composer, the parameter (before) runs first. So 3+1 = 4. Then the instance (after) runs making 4*2 = 8

Function<Integer, Integer> before = x -> x + 1;
Function<Integer, Integer> after = x -> x * 2;
Function<Integer, Integer> combined = after.compose(before);
System.out.println(combined.apply(3)); 

Fernando László Temesi Villagrán wrote:2) In Table 9.6, (page 485) it says

public V merge(K key, V value, Function(<V, V, V> func))

. It should be

public (default?) V merge(K key, V value, BiFunction<V, V, V> func)

.

Agreed. This is already in the errata.

Fernando László Temesi Villagrán wrote:Where could I find the whole erratas table for this book?

https://www.selikoff.net/ocp17/

[Manuel Trumm]

Jeanne Boyarsky wrote:

Guillaume Bailly wrote:Hi,

In the introduction on page xxxiii there is a small typo in my opinion.

"The review questions in each chapter are designed to help you home in..."

should be "...hone in..."

I'm not a native speaker, so my apologies if this was correct and I got it wrong.

Kind regards,
Guillaume

You are correct. I added it to the errata. Interestingly, it was right in the Java 11 book. And this isn't a part we change so an editor must have misread.

The errata item's page reference is currently "xxiiii" instead of the correctly reported "xxxiii".

[Manuel Trumm]

The ocp17 errata item:
xliv Intro #14 – || should be | Alessandro Putzu 8/22/22
is actually a ocp11 errata item and should read for ocp17:
lvii Intro #30 – || should be |

[Artuur Oerlemans]

Hi,
I noticed a mistake one page 908 and page 961. On page 908 question 21 says to pick 2 answers, according to page 961 those are B and D. However only answer B is correct.

The explanation on page 961 says that since line D is commented out, the update is lost. However since in the code example a try-with-resources is used on the connection, the connection gets closed. According to page 894, this an autocommit edge case of which the behaviour is undefined, therefor the update might be commited or rolled back. Meaning answer D is wrong, as the update might occur.

[Manuel Trumm]

Chapter 1, Review Question 5, Option B:
The answer is marked as false. However, if the object created on line 9 is eligible for GC after line 13, isn't it then also eligible for GC after line 14? Or does the System.gc() is interpreted as: the object might have been GCed and therefore might not in all cases be eligible i.e. it might not exist?

[Luiz Felipe Ribeiro]

Hi guys, the converted time, is okay?
It looks like that it should be 2:50 and not 12:50. (Chapter 4)

Sorry if this is not the right place to post

2022–06–20T06:50+05:30[Asia/Kolkata]    // GMT 2022–06–20 01:20
2022–06–20T07:50-05:00[US/Eastern]      // GMT 2022–06–20 12:50

[Campbell Ritchie]

Welcome to the Ranch

[Manuel Trumm]

Chapter 5, page 251 reads in the second last sentence of the page:
We ran rewrite our previous example [...]
and should be:
We can rewrite our previous example [...]

[Manuel Trumm]

Chapter 6, Review question 14 D looks correct to me, although the answer says wrong. Anyone?

[Manuel Trumm]

Luiz Felipe Ribeiro wrote:Hi guys, the converted time, is okay?
It looks like that it should be 2:50 and not 12:50. (Chapter 4)

Sorry if this is not the right place to post

2022–06–20T06:50+05:30[Asia/Kolkata]    // GMT 2022–06–20 01:20
2022–06–20T07:50-05:00[US/Eastern]      // GMT 2022–06–20 12:50

Looks right to me:

The calculation for the US/Eastern time into GMT is: 07:50 - (-05:00) = 12:50

Chapter 4 Page 194.

[Manuel Trumm]

Chapter 7, Review question 14 Option D, pages 410 & 934. The question uses "non-sealed" and the answers assumes that the question uses "nonsealed" (without the dash).
Looks incorrect to me, making option D correct.

Edit:
I just see this already in the errata.

[T Vergilio]

Hi Jeanne/Scott,

I hope you are both well. This is only a minor issue on page 565, last sentence of the section entitled Linking Streams to the Underlying data:

"First, it looks at the source and seeing three elements."

Did you mean to develop the thought process further here?

I'm enjoying the book so far, it is even better than previous editions. I love how the essential information is logically summarised in tables throughout the book. Really, really clear approach to organising the content!

[Guillaume Bailly]

Manuel Trumm wrote:Chapter 1, Review Question 5, Option B:
The answer is marked as false. However, if the object created on line 9 is eligible for GC after line 13, isn't it then also eligible for GC after line 14? Or does the System.gc() is interpreted as: the object might have been GCed and therefore might not in all cases be eligible i.e. it might not exist?

Yes, you're right. The book assumes the most "restrictive" here (and if it's eligible for GC somewhere in the code, it will always be so later on in the same code).

[Guillaume Bailly]

Manuel Trumm wrote:Chapter 6, Review question 14 D looks correct to me, although the answer says wrong. Anyone?

Notice that if class A is extended by B, then B is a subclass of A.

[Manuel Trumm]

Guillaume Bailly wrote:

Manuel Trumm wrote:Chapter 6, Review question 14 D looks correct to me, although the answer says wrong. Anyone?

Notice that if class A is extended by B, then B is a subclass of A.

Ah, I misunderstood "extended by". Thanks!

[Manuel Trumm]

Chapter 11, page 616, "Basics of Try-with-Resources":

Also, notice that parentheses are used to list those resources, and semicolons are used to separate the declarations. This works just like declaring multiple indexes in a for loop.

Multiple indexes in for loop are separated by commas, while multiple resources are separated by semicolons. In addition, the type can be declared only once in a for loop.
Hence I don't understand the "works just like".

[Manuel Trumm]

Chapter 12, page 711, Summary:

The exports directive specifies that a package should be accessible outside the module. It can optionally restrict that export to a specific package.

That should be "to a specific module"?

[Jeanne Boyarsky]

Manuel Trumm wrote:The errata item's page reference is currently "xxiiii" instead of the correctly reported "xxxiii".

Oops. Fixed

Manuel Trumm wrote:The ocp17 errata item:
xliv Intro #14 – || should be | Alessandro Putzu 8/22/22
is actually a ocp11 errata item and should read for ocp17:
lvii Intro #30 – || should be |

Agreed. Fixed

Artuur Oerlemans wrote:Hi,
I noticed a mistake one page 908 and page 961. On page 908 question 21 says to pick 2 answers, according to page 961 those are B and D. However only answer B is correct.

The book has two B and D. The errata says give yourself credit for D. So it is inconsistent but the book does match itself.

Manuel Trumm wrote:Chapter 1, Review Question 5, Option B:
The answer is marked as false. However, if the object created on line 9 is eligible for GC after line 13, isn't it then also eligible for GC after line 14? Or does the System.gc() is interpreted as: the object might have been GCed and therefore might not in all cases be eligible i.e. it might not exist?

The intent was first eligible for GC. I like your justification on why it isn't wrong though . We did it that way in our Java 8 and 11 books. That said, you did find a good edge case of interpretation. have a cow. I made a note to see if want to to add "first" next time.

Luiz Felipe Ribeiro wrote:Hi guys, the converted time, is okay?
It looks like that it should be 2:50 and not 12:50. (Chapter 4)

Sorry if this is not the right place to post

2022–06–20T06:50+05:30[Asia/Kolkata]    // GMT 2022–06–20 01:20
2022–06–20T07:50-05:00[US/Eastern]      // GMT 2022–06–20 12:50

I prefer separate threads because it makes it easier to track/reply. But I'd rather hear from readers even if it is in one large thread. I don't get 2:50 when I run it. What locale are you in. [edit: I see it works for Manuel too]

[Jeanne Boyarsky]

Manuel Trumm wrote:Chapter 5, page 251 reads in the second last sentence of the page:
We ran rewrite our previous example [...]
and should be:
We can rewrite our previous example [...]

Agreed and added to the errata

Manuel Trumm wrote:Chapter 6, Review question 14 D looks correct to me, although the answer says wrong. Anyone?

It's backwards Option D is. "If class A is extended by B, then B is a superclass of A"
If class A is extended by B means

class B extends A {}

This makes A the superclass of B which is the opposite of what option D says.

Edit: Guillaume explained this in the thread (I'm going in order)

T Vergilio wrote:Hi Jeanne/Scott,

I hope you are both well. This is only a minor issue on page 565, last sentence of the section entitled Linking Streams to the Underlying data:

"First, it looks at the source and seeing three elements."

Did you mean to develop the thought process further here?

Hmm. It was like that in the Java 11 book too. I think we meant to say "sees" and not "seeing". I'll put it in our list for the next edition.

[Jeanne Boyarsky]

Manuel Trumm wrote:Chapter 11, page 616, "Basics of Try-with-Resources":

Also, notice that parentheses are used to list those resources, and semicolons are used to separate the declarations. This works just like declaring multiple indexes in a for loop.

Multiple indexes in for loop are separated by commas, while multiple resources are separated by semicolons. In addition, the type can be declared only once in a for loop.
Hence I don't understand the "works just like".

Conceptually having multiple things

Manuel Trumm wrote:Chapter 12, page 711, Summary:

The exports directive specifies that a package should be accessible outside the module. It can optionally restrict that export to a specific package.

That should be "to a specific module"?

Yup! Added to the errata