Accessibility Example from Khalid Mughal-getting compilation errors

[Esther Kak]

I am trying to work on example 4.8(Pg No:116) but I could'nt compile

package Ekak.MyFavorites.Certification.KhalidMughal.PackageA;
 
class SuperClassA{
public int superClassVarA;
public void superClassMethodA()
{
System.out.println("This is the public method in superclassA of PackageA");
}
}

package Ekak.MyFavorites.Certification.KhalidMughal.PackageA;
class SubClassA extends SuperClassA
{
void subClassMethodA(){
superClassVarA = 10;
System.out.println("superClassVarA from subclass:"+superClassVarA);
}
}

Compilation Errors are below

symbol : class SuperClassA
location: class Ekak.MyFavorites.Certification.KhalidMughal.PackageA.SubClassA
class SubClassA extends SuperClassA{
^
C:\Ekak\My Favorites\Certification\KhalidMughal\PackageA\SubClassA.java:5: cannot resolve symbol
symbol : variable superClassVarA
location: class Ekak.MyFavorites.Certification.KhalidMughal.PackageA.SubClassA
superClassVarA = 10;
^
C:\Ekak\My Favorites\Certification\KhalidMughal\PackageA\SubClassA.java:6: cannot resolve symbol
symbol : variable superClassVarA
location: class Ekak.MyFavorites.Certification.KhalidMughal.PackageA.SubClassA
System.out.println("superClassVarA from subclass:"+superClassVarA);
^
3 errors

[Esther Kak]

Can somebody explain why this is not compiling?

[dhwani mathur]

Hi


i think the variable in the super class must be declared as
protected.............

so try the below code

  package Ekak.MyFavorites.Certification.KhalidMughal.PackageA; 
 
class SuperClassA{
protected int superClassVarA;
public void superClassMethodA(){
System.out.println("This is the public method in superclassA of PackageA");
}
}
  

 package Ekak.MyFavorites.Certification.KhalidMughal.PackageA;
class SubClassA extends SuperClassA
{
void subClassMethodA()
{
superClassVarA = 10;
System.out.println("superClassVarA from subclass:"+superClassVarA);
}
}
   

try the above code and
do let me know if it works...............

[Mark Uppeteer]

The syntax of the original code is fine. It compiles fine, no problem there.
No need to add protected or anything (read your K&B).

The reason this does not work is because you compile it wrong. you probably type in the javac instruction yourself, and your classpath is wrong.

please post the javac line.

grtz
mark

[Mohit Jain]

Use the compilation statement -

>javac -d . SuperClassA.java SubClassA.java

It creates the package directories automatically and compiles the code fine.

[Esther Kak]

Hi Mohit Jain,
I tried but it did not work with your compilation statement javac -d . SuperClassA.java SubClassA.java

PATH VARIABLE is
C:\j2sdk1.4.2_12\bin

CLASSPATH VARIABLE is
C:\Ekak\My Favorites\Certification\KhalidMughal
Both the following programs are in PackageA under khalidMughal directory.
Program1-SuperClassA.java
Accessibility is:

Class name - is default

Class variable - public

Class method - public

Program2 - SubClassA.java
SubClassA.java extends SuperClassA.java which is in the same package. And defines a simple method to access the superclass variable.

But the error I get is cannot resolve symbol: SuperClassA
I have the path variable set to point to the bin dir
I have my classpath variable set to point to KhalidMughal but not packageA

Why am I not able to compile the code. Need Help. Can anyone explain?

[Esther Kak]

Could anybody please reply on this!!! Thanks in Advance

[Mark Uppeteer]

hi Esther Kak ,

I 'managed' to reproduce your error because it always just seem to compile fine for me.
I get your error, when I execute compilation of the subclass without the superclass being on the same compilation line.

Position yourself in the folder of your java files.
javac SubClassA.java gives me:
----
SubClassA.java:2: cannot find symbol
symbol: class SuperClassA
class SubClassA extends SuperClassA
^
SubClassA.java:5: cannot find symbol
symbol : variable superClassVarA
location: class Ekak.MyFavorites.Certification.KhalidMughal.PackageA.SubClassA
superClassVarA = 10;
^
SubClassA.java:6: cannot find symbol
symbol : variable superClassVarA
location: class Ekak.MyFavorites.Certification.KhalidMughal.PackageA.SubClassA
System.out.println("superClassVarA from subclass:"+superClassVarA);
^
3 errors

----

but when I execute

javac SubClassA.java SuperClassA.java

everything compiles just fine.
This error occurs because you try to compile a class (SubClassA) that needs a superclass (SuperClassA) but SuperClassA.class doesn't exist yet (or isn't found).

[Mark Uppeteer]

now I see its even not the same error. yours is 'resolve', mine is 'find'.
Guess I didn't manage to reproduce your error after all.

Fact is that there is nothing wrong with the code. Its configuration.

[Esther Kak]

Thankyou for taking time to reproduce errors and solve it. Your answer helped me.