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visibility issue

5 replies on 1 page. Most recent reply: Aug 7, 2005 10:55 PM by rakesh kumar shukla

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rakesh kumar shukla

Posts: 6
Nickname: rakshukla
Registered: Jul, 2005

visibility issue

Posted: Aug 4, 2005 6:17 AM

please look at these classes
in <firstPackage.FirstClass> class static variable VAR_TO_TEST has visibility protected so if <secondPackage.SecondClass> class extends <firstPackage.FirstClass>, VAR_TO_TEST is visible. now as we can not assign less visibility to inherited variables so it should have protected visibilty in class <secondPackage.SecondClass> then why <secondPackage.CheckClass> is not able to get it ?
Whether I have to copy this variable into a instance static variable of secondPackage.SecondClass to make it available for secondPackage.CheckClass .
Please make me understand I am not good in OOP's funda

// FIRST CLASS
package firstPackage;

public class FirstClass {

protected static int VAR_TO_TEST = 0;

}
// FIRST CLASS ENDS HERE

// SECOND CLASS
package secondPackage;
import first.MyClass;

public class SecondClass extends FirstClass{

public static void main(String[] args) {
VAR_TO_TEST = 9;// VISIBLE HERE
}
}
// SECOND CLASS ENDS HERE

//CHECK CLASS
package secondPackage;
public class CheckClass {

public static void main(String[] args) {
SecondClass.VAR_TO_TEST = 9;// NOT VISIBLE HERE

}
}
// CHECK CLASS ENDS HERE

rakesh kumar shukla

Posts: 6
Nickname: rakshukla
Registered: Jul, 2005

Re: visibility issue

Posted: Aug 4, 2005 6:25 AM

please take the code as

// FIRST CLASS
package firstPackage;

public class FirstClass {

protected static int VAR_TO_TEST = 0;

}
// FIRST CLASS ENDS HERE

// SECOND CLASS
package secondPackage;
import firstPackage.FirstClass;

public class SecondClass extends FirstClass{

public static void main(String[] args) {
VAR_TO_TEST = 9;// VISIBLE HERE
}
}
// SECOND CLASS ENDS HERE

//CHECK CLASS
package secondPackage;
public class CheckClass {

public static void main(String[] args) {
SecondClass.VAR_TO_TEST = 9;// NOT VISIBLE HERE

}
}
// CHECK CLASS ENDS HERE

Kondwani Mkandawire

Posts: 530
Nickname: spike
Registered: Aug, 2004

Re: visibility issue

Posted: Aug 4, 2005 7:18 AM

> please take the code as
>
> // FIRST CLASS
> package firstPackage;
>
> public class FirstClass {
>
> protected static int VAR_TO_TEST = 0;
>
> }
> // FIRST CLASS ENDS HERE
>
>
> // SECOND CLASS
> package secondPackage;
> import firstPackage.FirstClass;
>
> public class SecondClass extends FirstClass{
>
> public static void main(String[] args) {
> VAR_TO_TEST = 9;// VISIBLE HERE
> }
> }
> // SECOND CLASS ENDS HERE
>
> //CHECK CLASS
> package secondPackage;
> public class CheckClass {
>
> public static void main(String[] args) {
> SecondClass.VAR_TO_TEST = 9;// NOT VISIBLE HERE
>
> }
> }
> // CHECK CLASS ENDS HERE

import static firstPackage.FirstClass.VAR_TO_TEST;

Though you'll have to make VAR_TO_TEST public
because they are from different packages.

Its not advisable to make copies of Static variables.
Take a look at Java's doc on static import:

http://java.sun.com/j2se/1.5.0/docs/guide/language/static-import.html

and *PLEASE* put pre tags around your code, its
really messy!! Check the Formatting your code
tip (it appears on your right when you're on the
post page).

Spike

Kondwani Mkandawire

Posts: 530
Nickname: spike
Registered: Aug, 2004

Re: visibility issue

Posted: Aug 4, 2005 7:21 AM

Oh I forgot to mention the above only applies if you're
using Java 5.

Spike

Ravi Venkataraman

Posts: 80
Nickname: raviv
Registered: Sep, 2004

Re: visibility issue

Posted: Aug 5, 2005 2:47 PM

The CheckClass has access only to the public variables and methods of SecondClass. Since the variable SecondClass.VAR_TO_TEST has "protected" access, it is visible only to sub-classes of SecondClass.

To grant visibility to any class, you can either define the variable to be public in FirstClass, or provide a public "getter" function in SecondClass (or even in FirstClass.)

rakesh kumar shukla

Posts: 6
Nickname: rakshukla
Registered: Jul, 2005

Re: visibility issue

Posted: Aug 7, 2005 10:55 PM

But Ravi
I think protected members are accessible in the same package by other classes.

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