[online] OCA/OCP Java SE 8 Practice Tests OCA mock question 79 errata

[Rune Thode]

Some errors have sneaked into question 79 of the online mock OCA test.

As can be seen on the image, the Bear class names do not match. The class itself is with lower case 'b', where it is with upper case in the child class.
Then there is a date line that shouldn't be there at all. Both errors are not in the book.

[Campbell Ritchie]

There isn't a “following class”. There are two classes. Assuming the line about dates (No 17) shouldn't be there, and assuming there is no Bear class, I found four compile‑time errors:-

javac PolarBear.java
PolarBear.java:5: error: cannot find symbol
   protected in sing;
             ^
 symbol:   class in
 location: class bear
PolarBear.java:15: error: cannot find symbol
public class PolarBear extends Bear
                              ^
 symbol: class Bear
PolarBear.java:19: error: cannot find symbol
       sing() += 10;
       ^
 symbol:   method sing()
 location: class PolarBear
PolarBear.java:20: error: cannot find symbol
       return super.grunt() + 1;
              ^
 symbol:   variable super
 location: class PolarBear
4 errors

1: There is no such datatype as in; maybe it should read int.

2: The Bear class doesn't exist, so it cannot be extended.

3: The returned type from sing() is a value, not a variable, and cannot therefore be the target of the += operator.

4: The superclass doesn't have an implementation for sing(), so the keyword super won't work.

Note how helpful the error messages are sren't.

[Rune Thode]

The error messages are not very helpful...

I forgot about the "datatype" in. In the book, it is correctly an int and the Bear class is called Bear, which then results in the error that grunt() cannot be overloaded with a stricter access modifier.

[Campbell Ritchie]

I am getting confused; which errors are in that screenshot and also in the exam itself? When I removed the part about dates, I got three error messages, all on different lines:-

javac -d . PolarBear.java
PolarBear.java:17: error: grunt() in PolarBear cannot override grunt() in Bear
   int grunt()
       ^
 attempting to assign weaker access privileges; was protected
PolarBear.java:19: error: unexpected type
       sing() += 10;
           ^
 required: variable
 found:    value
PolarBear.java:20: error: abstract method grunt() in Bear cannot be accessed directly
       return super.grunt() + 1;
                   ^
3 errors

[edit]The below image shows why we prefer not to see screenshots if at all possible.

[Charles O'Leary]

Rune Thode wrote:Some errors have sneaked into question 79 of the online mock OCA test.

As can be seen on the image, the Bear class names do not match. The class itself is with lower case 'b', where it is with upper case in the child class.
Then there is a date line that shouldn't be there at all. Both errors are not in the book.

Rune Thode wrote:In the book, it is correctly an int and the Bear class is called Bear

The online experience does not appear to be under the authors' control.  I try to stick strictly to each book and its respective errata for the best experience.

[Rune Thode]

Campbell Ritchie wrote:There isn't a “following class”. There are two classes. Assuming the line about dates (No 17) shouldn't be there, and assuming there is no Bear class, I found four compile‑time errors

The code in the book:

package arctic;
abstract class Bear {
    protected int sing;
    protected abstract int grunt();
    int sing() {
        return sing();
    }
}

public class PolarBear extends Bear {
    int grunt() {
        sing() += 10;
        return super.grunt()+1;
        return 10;
    }
}

The code in the online test:

package arctic;
abstract class bear {
    protected in sing;
    protected abstract int grunt();
    int sing() {
        return sing();
    }
}

public class PolarBear extends Bear {
    int grunt() {
        sing() += 10;
        return super.grunt()+1;
    }
}
    date = date.minusMonths

The explanation for the the answer is the same in both versions:

Line 10 does not compile because the override reduces the visibility of an inherited method, with the package-private modifier being more restrictive than the protected modifier. Line 11 does also not compile, since the left-hand side of a compound assignment operator must be used with a variable, not a method. Finally, Line 12 does not compile because super.grunt() is inherited as an abstract method in the PolarBear class, meaning the parent class has no implementation. For these three reasons, Option D is the correct answer.

So the differences are:

Line 2: bear instead of Bear

Line 3: protected in sing instead of protected int sing;

Line 13.5: There is only one return statement (there are two in the book).

Charles O'Leary wrote:The online experience does not appear to be under the authors' control.  I try to stick strictly to each book and its respective errata for the best experience.

I thought you were also working on the online version. I did just notice that there are two return statements in the book version, which is not mentioned in the answer.
The version I have is this one

[Charles O'Leary]

Rune Thode wrote:

Charles O'Leary wrote:The online experience does not appear to be under the authors' control.  I try to stick strictly to each book and its respective errata for the best experience.

I thought you were also working on the online version.

Rune,

To be perfectly honest, I'm now sticking to the book itself only.  When I want to better "emulate" the real computer oriented (mock) testing experience, I personally have found https://enthuware.com/ to contain less/no errors.  Enthuware even has a 100% money back refund to that effect.  

Kudos to Jeanne, Scott, and Enthuware!

[Rune Thode]

Alright that makes sense. I have been very satisfied with the online version, I just wanted to point out the errors, I found.

[Jeanne Boyarsky]

Yeah. It's right in the physical book!

I've added it to the errata as an online only problem.