Bugtraking Devaka's Examlab

[Anastasia Sirotenko]

Was working through 2nd exam round in Devaka's ExamLab (great software, i rely upon it to clear my future exam), found this bug in 27 question:


the answer is definitly should be something like " Boolean.parseBoolean(String) returns boolean value, not Boolean object, so you cannot call a getClass() method on boolean value"

[Anastasia Sirotenko]

And one more may-be-bug (or i messed somewhere in my code and cannot find where)
The answer in ExamLab is:

But i ran the code:

    
class B extends A{}
class C extends B{}
class A{
    public static void main(){
        A a = new B();
        B b = new B();
        C c = new C();
        C[] ca = null;
        a = b;
        b = c;
        A a1 = (B)c;
        Runnable r1 = (Runnable)a;
        Runnable[] ra1 = null;
        A r2 = (A)r1;
        A[] aa1 = (A[])r1; // error
        A[] aa2 = (A[])ra1;
        ra1 = (Runnable[])ca;  //OK!
    }
}

ra1 = (Runnable[])ca; is defenetly compiles fine, it´s the same case as A[] aa2 = (A[])ra1; if i am not wrong.

PS My bad, i did not notice final modifier for class C, Devaka's code is good (tho evil!), surely now i will take more attention in future for such things, really great simulator 8)

[Ankit Garg]

Anastasia Sirotenko wrote:the answer is definitly should be something like " Boolean.parseBoolean(String) returns boolean value, not Boolean object, so you cannot call a getClass() method on boolean value"

Check the java.lang.Boolean class documentation. There is no parseBoolean method in it.

In your second code, you missed final before the class C...

[Nitish Bangera]

Ankit parseBoolean is definitely there in the Boolean wrapper which gives out a boolean. Also it is case insensitive. The correct answer will be yes the primitive value cannot get a class. Well as for the second one, before casting think you apply a instanceof well instanceof is like on the right side there can be any interface but on the left of the instanceof there should be a non final class. Well same applies here. And if arrays are there then nonfinal class array instance of interface array >---->(Interface array)non final class array and not (Interface array)non final class. I guess this was there in the examlab.

[Anastasia Sirotenko]

Ankit Garg wrote:

Anastasia Sirotenko wrote:the answer is definitly should be something like " Boolean.parseBoolean(String) returns boolean value, not Boolean object, so you cannot call a getClass() method on boolean value"

Check the java.lang.Boolean class documentation. There is no parseBoolean method in it.

http://java.sun.com/javase/6/docs/api/java/lang/Boolean.html#parseBoolean(java.lang.String) here it is...

Ankit Garg wrote:your second code, you missed final before the class C...

Thank you very much! Here i get it 8)
It's not a Devaka's mistake, but mine here 8)

[Anastasia Sirotenko]

Nitish Bangera wrote:Well as for the second one, before casting think you apply a instanceof well instanceof is like on the right side there can be any interface but on the left of the instanceof there should be a non final class. Well same applies here. And if arrays are there then nonfinal class array instance of interface array >---->(Interface array)non final class array and not (Interface array)non final class. I guess this was there in the examlab.

Yes, i was mistaken with this final class, did not notice it, thank you 8)

[Ankit Garg]

Nitish Bangera wrote:Ankit parseBoolean is definitely there in the Boolean wrapper which gives out a boolean.

I messed up

[Lucas Smith]

Nitish Bangera wrote:Ankit parseBoolean is definitely there in the Boolean wrapper which gives out a boolean.

So there is a bug in K&B book (rhyme )
Page 243 - parseBoolean is not marked.

[Devaka Cooray]

Thanks for noticing. The first one is an error with the explanation, and it is already discovered before. - Will be fixed with the next update

Devaka.

[Devaka Cooray]

Anastasia,

What is the screen resolution you are using there?
The appearance of the "Copy Program" button in your screenshot makes me confused.

[Nitish Bangera]

I hope you put the description for the formatter questions also. Little better than pointing to J2SE documention.

[Anastasia Sirotenko]

Devaka Cooray wrote:Anastasia,

What is the screen resolution you are using there?
The appearance of the "Copy Program" button in your screenshot makes me confused.

I am using 1280x1024 resolution. Realy did not pay attention how things look 8)
Great training software, Devaka, thank you for that!