Compiling errata for K&B, SCJP 6

[Bob Condon]

Ch. 3 Qn. 12
My output was "4 6" - which is not a choice in the book.
go() method listed b2, b1 out of order...so, book choice of "6 4" is good answer.

 class Box {
    int size;
    Box(int s) { size = s; }
}
public class Laser {
    public static void main(String[] args){
        Box b1 = new Box(5);
        Box[] ba = go(b1, new Box(6));
        ba[0] = b1;
        for(Box b : ba) System.out.print(b.size + " ");
    }
    static Box[] go(Box b1, Box b2) {
        b1.size = 4;
        Box[] ma = {b1, b2};
        return ma;
    }

}

[Vijay Tyagi]

There is a line in Chapter 1 of KB SCJP 6 book

"Finally, you need to know that the abstract modifier can never be combined
with the static modifier."

on
page 45


Static nested classes can be abstract ,so it is not entirely true.


It is under the topic Non access modifiers for members so it's right , but this statement can be a bit misleading.

[Yalvin Duha]

I don't know if this is a valid errata, but Chapter 7, Self-Test section, Question 3 (answered on page 648-649) says that the correct choice is "E" (a run-time error).

Frankly, I don't know whether inclusion of proper "import" statements/packages/classes only applies when the code contains the class definition, i.e. public class Animal { }, but given the code as is, it would not compile because of a missing "import java.util.*" statement.

--------------------

Chapter 7, Self-Test, Question 7 (answered on page 653-654): although the answer is "B", the output is partially correct. When a PriorityQueue is empty and peek() is called, it returns "null". Therefore, the output should also contain "null".

The correct answer is (B) 2 2 3 4 null

--------------------

Chapter 7, Self-Test, Question 13: at no point in the chapter SortedMap.firstKey() was mentioned or said to be required to be on the exam. Nonetheless, the question relies on it for the answer. Please clarify whether this method and others in SortedMap/SortedSet , that are not mentioned in the book, are going to be on the test.

[Carrie Hall]

I may be missing something here, but I tried to compile Chapter 7 Self Test - q1 and could not compile any of the listed answers.

B is meant to be the answer, i.e.

List<List<Integer>> table = new ArrayList<List<Integer>>();

but I get a compilation error :

The type List is not generic; it cannot be parameterized with arguments <Integer>

[sarvesh dikonda]

Martin Leon wrote:Chapter 10 Self Test, Question 2, page 811, 812

My book has a "." after the "A" as part of the command line that is invoked. None of the answers have a ".", so none of them are correct.

Try it:

import static java.lang.System.*; 

class _ {
	static public void main(String... __A_V_) {
		String $ = ""; 

		for(int x=0; ++x < __A_V_.length; )
			$ += __A_V_[x];
		
		out.println($);
	}
}

java _ - A .

You are wrong Martin Leon when you compile and run the above code it prints A. i.e it prints the Letter 'A' with a dot(.) Try once again

[Chris Devine]

In the Chapter 1 Self-test, question 6:

6. Given:

1. public class Electronic implements Device { public void doIt() { } }
2.
3. abstract class Phone1 extends Electronic { }
4.
5. abstract class Phone2 extends Electronic { public void doIt(int x) { } }
6.
7. class Phone3 extends Electronic implements Device { public void doStuff() { } }
8.
9. interface Device { public void doIt(); }

What is the result? (Choose all that apply.)
A. Compilation succeeds
B. Compilation fails with an error on line 1
C. Compilation fails with an error on line 3
D. Compilation fails with an error on line 5
E. Compilation fails with an error on line 7
F. Compilation fails with an error on line 9

Answer:
A is correct; all of these are legal declarations.
B, C, D, E, and F are incorrect based on the above information. (Objective 1.2)

The answer given (A. Compilation succeeds) seems incorrect. If the Device interface contains the method public void doIt(), then all classes implementing that interface should implement that method. However, the class Phone 3 implements the Device interface but only implements a doStuff() method. This would cause a compile error due to a mistake on line 7. Answer E should be the correct answer in that case.

[Fred Butler]

Chris Devine wrote:In the Chapter 1 Self-test, question 6:

The answer given (A. Compilation succeeds) seems incorrect. If the Device interface contains the method public void doIt(), then all classes implementing that interface should implement that method. However, the class Phone 3 implements the Device interface but only implements a doStuff() method. This would cause a compile error due to a mistake on line 7. Answer E should be the correct answer in that case.

Hi Chris,

The answer in the book is correct.
Note that "Phone3 extends Electronic" and that "Electronic implements Device { public void doIt() { } }"
Hence, Phone3 inherits the "public void doIt() { }" implementation from Electronic.
Aside, there's no need for Phone3 to explicitly state it implements Device, since Phone3 already inherits that interface from Electronic.

Regards,
Al

[Chris Devine]

Alan Cowap wrote:

Chris Devine wrote:In the Chapter 1 Self-test, question 6:

The answer given (A. Compilation succeeds) seems incorrect. If the Device interface contains the method public void doIt(), then all classes implementing that interface should implement that method. However, the class Phone 3 implements the Device interface but only implements a doStuff() method. This would cause a compile error due to a mistake on line 7. Answer E should be the correct answer in that case.

Hi Chris,

The answer in the book is correct.
Note that "Phone3 extends Electronic" and that "Electronic implements Device { public void doIt() { } }"
Hence, Phone3 inherits the "public void doIt() { }" implementation from Electronic.
Aside, there's no need for Phone3 to explicitly state it implements Device, since Phone3 already inherits that interface from Electronic.

Regards,
Al

Thanks, Al. I see that now. One my biggest difficulties (being new to Java and coding in general) is being able to see when and how things work even if they violate good programming practices and conventions. Having a class implement an interface that its superclass already implements appears to be one of those cases where just because it's legal doesn't mean it's right.

All the best,
Chris

[Francky Boy]

SELF TEST Page 82, question 7.
Answer:
C,D, and F are correct.

F is wrong !

What is wrong on the enum on line 10, compilation succeeds.

[Fred Butler]

Francky Boy wrote:SELF TEST Page 82, question 7.
Answer:
C,D, and F are correct.

F is wrong !

What is wrong on the enum on line 10, compilation succeeds.

In J2SE version 6, F won't compile:
"The member enum Traffic can only be defined inside a top-level class or interface"
- but it's defined within a method, hence the compiler error.

You could check that you've typed the code correctly, and that you're using the correct compiler (version 6).

Regards,
Al

[Francky Boy]

In J2SE version 6, F won't compile:
"The member enum Traffic can only be defined inside a top-level class or interface"
- but it's defined within a method, hence the compiler error.

You could check that you've typed the code correctly, and that you're using the correct compiler (version 6).

Regards,
Al

You're right ! When I try that example under Eclipse with compiler version 6 , the enum line wasn't red !

Thanks and Regards

[Shannon Sims]

Error??? Page 76, question #7, the answer on page 83 states that C, D and F are correct. However, since line 9 is not initialized, this should be a compile error according to page 71 - "Local Variables - Local variables don't get default values, so they must be initialized before use". Therefore, the answer should be C, D, E and F, please verify?

Thank you.

Never mind, the key word to watch for was "before use".

[Joe Boman]

doubt in k&b, page 92,
currently reads:
....that the PlayingPiece class inherits the generic display() method...

maybe should read:
...that the PlayerPiece class inherits the generic displayShape() method...

There are other references to the display() method

[Omar Nassar]

I would like to thank you all for these feedback

[Jon Frowd]

In the question posed on page 433, aren't 9 objects created? Isn't the space character on the last line also a String object?

System.out.println(s1 + " " + s2);

[Steven Squeers]

Jon Frowd wrote:In the question posed on page 433, aren't 9 objects created? Isn't the space character on the last line also a String object?

System.out.println(s1 + " " + s2);

String literals are different to String objects. String s = "x" is not the same as String s = new String("x"). AFAIK the former creates a String literal in the String pool, unless the literal already exists, in which case it doesn't; the latter always creates a new String object.

[Daya Moon]

Chapter 5. page 398.
line7th from the bottom
Using break and continue (Objective 2.2)
"An unlabeled break statement will cause the current iteration of the innermost looping construct to stop and, the line of code following the loop to run."
As break will exit the loop.

[Daya Moon]

Jon Frowd wrote:In the question posed on page 433, aren't 9 objects created? Isn't the space character on the last line also a String object?

System.out.println(s1 + " " + s2);

Until
System.out.println() there will be 8 objects created.

String s1 = "spring ";                          // "spring"  (1)
String s2 = s1 + "summer ";                   //  "summer" and  "spring summer" (2)
s1.concat("fall ");                               //  "fall"        and  "spring fall"         (2)
s2.concat(s1);                                   //  "spring summer spring"               (1)
s1 += "winter ";                                // "winter"     and "spring winter"      (1)

//8 of all till now
System.out.println(s1 + " " + s2);     // space(1),   "spring winter" + space (2)    and  "spring summer space" + "spring summer" (3)

[Math Silva]

Page 682. Last sentence says:

Rember, static inner classes can't access instance methods or variables.

I believe it should be "static nested class", right?

[YinLi Tao]

Bert Bates wrote:

Also, THANKS to everyone for posting these! I tend to look into these in baches, so pretty soon I'll review all of these and give you all some feedback!

Bert

Hi,

I'm trying to find the official errata for SCJP Sun Certified Programmer for Java 6: Exam 310-065 book. The publisher's errata list doesn't list such. Is this thread what I'm looking for? Where can I find the feedback Bert mentioned in his post?

[Richard Hayward]

Chapter 9: Threads self test q15

With either fragment, the first output must be yo.

I don't think this is so. It's possible for 'dude' to get printed first.

https://coderanch.com/t/657902/java-programmer-SCJP/certification/SCJP-Chapter-Threads-test