ExamLab 2nd exam 58th

[Kaladhar Ak]

Hi all

This question is 58 from ExamLab's 2nd exam.

clasA.java
--------------

package pkga;
public class clasA{
protected void doThis(){}
}



===================================


clasB.java
----------------

package pkgb;
import pkga.clasA;
public class clasB extends clasA{
public static void main(String args[]){
/* Insert Here */
ca.doThis();
}
}

Correct answers mentioned are ClasB ca = new ClasB(); and ClasB ca = new ClasB(){protected void doThis(){}};
I didnt get the point that how to call a protected method using its instance in a different package? Second answer looks correct but not the first one. Can any one explain please?

[Ruben Soto]

Welcome to the ranch, Kaladhar.

The only restriction is that you can't call a protected method through a reference of the superclass from outside the superclass package. The way the JLS puts it is that you can only call protected methods outside the package from within the class which is responsible for the implementation. The thing that might be confusing you in this case is that classB doesn't override the doThis() method. However, it's up to classB's implementor to do so (by not overriding it, classB is deciding to use the same implementation as the superclass.) The point is that you are calling the method on a reference of classB, from classB.

[Ankit Garg]

Kaladhar, please Use Code Tags the next time you post any source code.

Now just to elaborate on a point that Ruben mentioned, if you try to access the protected member via inheritance, then you can access it otherwise not. So if you try to do this

package a;

class A {
    protected void method() {}
}

package b;

import a.A;

class B extends A {
    public static void main(String[] args) {
        B b = new B();
        b.method();  //ok
        A a = new A();
        a.method();  //error, method is inaccessible
    }
}

[Kaladhar Ak]

Hi Ruben and Ankit,

Thanks for reply. But in the question, doThis() is referenced outside the superclass package with superclass reference (from to one of the correct answers). Isn't it wrong?

Regards
Kaladhar

[Treimin Clark]

Kaladhar Ak wrote:Hi Ruben and Ankit,

Thanks for reply. But in the question, doThis() is referenced outside the superclass package with superclass reference (from to one of the correct answers). Isn't it wrong?

Regards
Kaladhar

You can't call it with a ClasA reference. You must have a ClasB reference. As you said, correct answers are ClasB ca = new ClasB(); and ClasB ca = new ClasB(){protected void doThis(){}};

[Treimin Clark]

Ankit Garg wrote:

package a;

class A {
    protected void method() {}
}

Hay Ankit, class A must be public here.

[Ankit Garg]

Treimin Clark wrote:

Ankit Garg wrote:

package a;

class A {
    protected void method() {}
}

Hay Ankit, class A must be public here.

Yes, you got me

[Kaladhar Ak]

Ruben,Ankit

Thanks for replies. It is clear now.

[Amit Ghorpade]

"Kaladhar Ak " please check your private messages for an important administrative matter. You can check them by clicking the My Private Messages link above.