Questions/errata for Sybex OCP 17 Study Guide

[Michael Goshey]

This may not be considered "errata", but I wonder if I'm the only one that finds the first row from Table 4.5 on page 187 ("Equality vs. comparison vs. mismatch") a bit ambiguous/confusing when it indicates that equals() returns true "When arrays contain the same data", since I believe the statement is only accurate when the references point to the same array object.

String[] bugs = { "cricket", "beetle", "ladybug" };
String[] alias = bugs;
String[] sameBugs = { "cricket", "beetle", "ladybug" };
System.out.println(bugs.equals(alias));//true
System.out.println(bugs.equals(sameBugs));//false

[Jeanne Boyarsky]

While you are correct, the table is about static methods on the Arrays class. See the last two lines in the following example:

Your example uses the equals() method defined on Object which as you've noted uses object equality. That's why Arrays.equals() exists. So you can compare arrays logically.

import java.util.*;
public class MyClass {
    public static void main(String args[]) {
      String[] bugs = { "cricket", "beetle", "ladybug" };
      String[] alias = bugs;
      String[] sameBugs = { "cricket", "beetle", "ladybug" };
      System.out.println(bugs.equals(alias));//true
      System.out.println(bugs.equals(sameBugs));//false
      System.out.println(Arrays.equals(bugs, alias));//true
      System.out.println(Arrays.equals(bugs, sameBugs));//true
    }
}

[Michael Goshey]

Thanks for clarifying what I missed!

[Michael Goshey]

Possible errata: Chapter 9, page 512, first paragraph after the heading "Bounding Generic Types": the second sentence reads "Bounded wildcards solve this by restricting what types can be used in a wildcard (emphasis mine)." It seems like that last word should be generic.

[Jeanne Boyarsky]

Michael Goshey wrote:Possible errata: Chapter 9, page 512, first paragraph after the heading "Bounding Generic Types": the second sentence reads "Bounded wildcards solve this by restricting what types can be used in a wildcard (emphasis mine)." It seems like that last word should be generic.

Hmm. I think that was trying to say the wildcard restricts the generic so either word would work, but the emphasis would be different.

I noted it on our private lists to consider whether it should be reworded next time. Thanks!

[Michael Goshey]

Chapter 10, page 564, bottom of page under the bold heading "getSum()": the explanation mentions DoubleSummaryStream, IntSummaryStream and LongSummaryStream, which presumably should be DoubleSummaryStatistics, IntSummaryStatistics and LongSummaryStatistics respectively.

[Jeanne Boyarsky]

Michael Goshey wrote:Chapter 10, page 564, bottom of page under the bold heading "getSum()": the explanation mentions DoubleSummaryStream, IntSummaryStream and LongSummaryStream, which presumably should be DoubleSummaryStatistics, IntSummaryStatistics and LongSummaryStatistics respectively.

I agree that should be changed next time. It was pointed out here

My response was

Thanks for the comment. We meant the type of the stream the summary statistics object came from. So it's not quite an errata. I do see how it could be clearer though so I put it on our private list of things to consider for the next version of the book.

Now that a second person said it, I lean more towards changing it!

[Michael Goshey]

Jeanne Boyarsky wrote:Now that a second person said it, I lean more towards changing it!

Or maybe just modify the monospace font, which sort of implies they are actual classes.

[Asiel Leal Celdeiro]

Hi,

I'm reading OCP Oracle Certified Professional Java 17 SE Developer Study Guide, and I'm struggling to understand the following:

On page 399 (Chapter 7 Beyond Classes > Understanding Polymorphism > Overriding vs. Hiding Members), in the last paragraph, is says "[...] it prints 3 instead of 8 [...]", but it actually prints 8 because the object reference is `CrestedPenguin`, whose static method `getHeight` returns 8. FWIW, I tested it in jshell (java 17.0.2)

So, I think, either the code snippet should be `new Penguin().printInfo();` or change text to "[...] it prints 8 instead of 3 [...]", but I guess this would defeat the purpose of the example, wouldn't it?

Does this make sense, or am I missing something here?

See attached image:

[Asiel Leal Celdeiro]

Ok, FWIW, it does print 3 if I run this code as an actual Java class.

Asiel Leal Celdeiro wrote:Hi,

I'm reading OCP Oracle Certified Professional Java 17 SE Developer Study Guide, and I'm struggling to understand the following:

On page 399 (Chapter 7 Beyond Classes > Understanding Polymorphism > Overriding vs. Hiding Members), in the last paragraph, is says "[...] it prints 3 instead of 8 [...]", but it actually prints 8 because the object reference is `CrestedPenguin`, whose static method `getHeight` returns 8. FWIW, I tested it in jshell (java 17.0.2)

So, I think, either the code snippet should be `new Penguin().printInfo();` or change text to "[...] it prints 8 instead of 3 [...]", but I guess this would defeat the purpose of the example, wouldn't it?

Does this make sense, or am I missing something here?

See attached image:

[Michael Goshey]

Asiel Leal Celdeiro wrote:Ok, FWIW, it does print 3 if I run this code as an actual Java class.

The code in the text (within main()) actually calls

.printInfo()

, whereas your code appears to be calling

.getHeight()

directly. Switch it to call printInfo() and you should get the appropriate result. Cheers!

[Kam M'Intosh-'i'i]

Where is the complete (to date) errata presented?  How can I access it?  I love the book and its presentation.  But, after seeing a couple of errors, I have become apprehensive about the book's contents.  A complete errata would boost my confidence in it.

[Asiel Leal Celdeiro]

Kam M'Intosh-'i'i wrote:Where is the complete (to date) errata presented?  How can I access it?  I love the book and its presentation.  But, after seeing a couple of errors, I have become apprehensive about the book's contents.  A complete errata would boost my confidence in it.

It's here: https://www.selikoff.net/ocp17/

[Mike Simmons]

Jeanne Boyarsky wrote:

Thanks for the comment. We meant the type of the stream the summary statistics object came from. So it's not quite an errata. I do see how it could be clearer though so I put it on our private list of things to consider for the next version of the book.

Now that a second person said it, I lean more towards changing it!

Hi, Jeanne!  I'm not sure I follow the first explanation - DoubleSummaryStream isn't a thing.  You can use a DoubleStream to get DoubleSummaryStatistics.  Then again, I don't know exactly how this appeared in the book - maybe it made more sense there.

[Michael Goshey]

Question on Chapter 14 I/O: This is one of those "...this is probably a really dumb question" moments, but I'm hoping you can clear up something that's been puzzling me. I'm just wrapping up your excellent Chapter on IO. Copious coverage is given to building blocks like the creation of File (IO) and Path (NIO.2) objects, directory creation methods for both I/O and NIO.2 and a wealth of necessary and related classes and methods, but I've not seen any mention of the actual API mechanisms for simply creating new empty files on disk. In other words, I can't seem to find any references in the chapter to either the java.io.File createNewFile() instance method, nor the corresponding NIO.2 Files.createFile() static method, and I'm sort of curious if I just missed this somehow or if there's some (embarrassingly) obvious reason why it isn't included- for example- in table 14.4 (page 793-794) which does include mkdir() and createDirectory()? Thanks for your time and for greatly accelerating my certification prep!

[Michael Goshey]

In Chapter 15 "JDBC", page 889, under the heading "Passing an IN Parameter," the second sentence reads: "The read_names_by_letter() stored procedure takes a parameter for the prefix or first letter of the stored procedure." It seems like the intention of the sentence makes more sense if revised to: "The read_names_by_letter() stored procedure takes a parameter for the prefix or first letter of the name column."

[Jeanne Boyarsky]

Mike Simmons wrote:

Jeanne Boyarsky wrote:

Thanks for the comment. We meant the type of the stream the summary statistics object came from. So it's not quite an errata. I do see how it could be clearer though so I put it on our private list of things to consider for the next version of the book.

Now that a second person said it, I lean more towards changing it!

Hi, Jeanne!  I'm not sure I follow the first explanation - DoubleSummaryStream isn't a thing.  You can use a DoubleStream to get DoubleSummaryStatistics.  Then again, I don't know exactly how this appeared in the book - maybe it made more sense there.

We referred to something that people interpretted as a class that wasn't. I agree that's not good .

[Jeanne Boyarsky]

Michael Goshey wrote:Question on Chapter 14 I/O: This is one of those "...this is probably a really dumb question" moments, but I'm hoping you can clear up something that's been puzzling me. I'm just wrapping up your excellent Chapter on IO. Copious coverage is given to building blocks like the creation of File (IO) and Path (NIO.2) objects, directory creation methods for both I/O and NIO.2 and a wealth of necessary and related classes and methods, but I've not seen any mention of the actual API mechanisms for simply creating new empty files on disk. In other words, I can't seem to find any references in the chapter to either the java.io.File createNewFile() instance method, nor the corresponding NIO.2 Files.createFile() static method, and I'm sort of curious if I just missed this somehow or if there's some (embarrassingly) obvious reason why it isn't included- for example- in table 14.4 (page 793-794) which does include mkdir() and createDirectory()? Thanks for your time and for greatly accelerating my certification prep!

It wasn't included because it isn't on the test. Creating an empty directory is more common than creating an empty file.

Also, creating an empty file can be done by writing an empty string (or list) to it. So less essential for people to know the method.

[Jeanne Boyarsky]

Michael Goshey wrote:In Chapter 15 "JDBC", page 889, under the heading "Passing an IN Parameter," the second sentence reads: "The read_names_by_letter() stored procedure takes a parameter for the prefix or first letter of the stored procedure." It seems like the intention of the sentence makes more sense if revised to: "The read_names_by_letter() stored procedure takes a parameter for the prefix or first letter of the name column."

Agreed that is an errata. Added to list and credited you!

[Caleb Josue Ruiz Torres]

Hello there all, I am not sure if this was already mentioned.


In the section Declaring static Interface Methods (Located in Chapter 7)

(First example of this method)
The Skip class is not implementing Hop. Therefore, it can't access getJumpHeight().

This is an amazing book.


--
Caleb

[Jeanne Boyarsky]

Confirmed and added to the errata. Thanks Caleb!

[Caleb Josue Ruiz Torres]

Hello there all,

Table 10.7 contains some methods on Stream classes that shouldn't include space. e.g. `IntUnary Operator` shall be `IntUnaryOperator`. There are several functions in this table containing spaces.

Thanks!



--
Caleb