Mock explanations #14 of chapter 3 (Java OCA 8 Programmer I Study Guide)

[Mushfiq Mammadov]

Hi,

When I check my answers for review questions of chapter 3 I saw that my answer of #14 question is correct. But I look at explanation of this question I know that I think wrong in really. Because I forget one detail in this question. I remember substring don't change StringBuilder when I saw explanation. If option B returns "avaJ" I would choose it as correct answer. If we run this code we saw that option B returns "Java" so I didn't consider it as correct answer.

StringBuilder puzzle = new StringBuilder("Java");
// puzzle.reverse();
puzzle.append("vaJ$").substring(0, 4);    //Output: Java

But explanation of #14 is written:

Option B is a nice distraction it does in fact return "avaJ". However, substring() returns a String, which is not stored anywhere.

Probably authors forget to put comment puzzle.reverse(); when run this code.

[Roel De Nijs]

The answers given in the book are correct: A and C will print the required avaJ.

The explanation why B is wrong, is wrong itself If you would print the String returned by option B

puzzle.append("vaJ$").substring(0, 4);

Java is indeed printed and not avaJ. Therefore it's definitely an incorrect answer (as mentioned in the book). But with the code as-is it's also not a nice distraction as the book suggests. To be a nice distraction option B should be replaced with

puzzle.reverse().append("vaJ$").substring(0, 4);

With this statement the explanation why B is wrong, would be correct.

And what about the last part of the eplanation of this question: and length() counts starting with 1?

StringBuilder sb = new StringBuilder();
System.out.println(sb.length()); // 0

Does length() not start with 0? Although I understand what's meant here, I wonder if it would not be better (as in more obvious/clear) to just state that length() just returns the character count.

[Jeanne Boyarsky]

You are both correct. Noted.