About Question com.enthuware.ets.scjp.v6.2.455 :

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1Z0-808, 1Z0-809, 1Z0-815, 1Z0-816, 1Z0-817

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stessy
Posts: 7
Joined: Sat Nov 12, 2011 5:38 am
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About Question com.enthuware.ets.scjp.v6.2.455 :

Post by stessy »

Hi,

I don't understand this question.

Why cannot we access the instance variable when they are in different packages. While we can access the same variable when they are in the same package.

If B is not involved in the implementation of A, the behavior should be the same whether or not the classes are in the same package.

Code: Select all

package be.p2;

public class B extends A {
    public void process(A a) {
        a.i = a.i * 2;
    }

    public static void main(String[] args) {
        A a = new B();
        B b = new B();
        b.process(a);
        System.out.println(a.getI());
    }
}

package be.p2;

public class A {
    protected int i = 10;

    public int getI() {
        return i;
    }
}
This code works and "20" is printed.

Thanks a lot for you help.

admin
Site Admin
Posts: 8992
Joined: Fri Sep 10, 2010 9:26 pm
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Re: About Question com.enthuware.ets.scjp.v6.2.455 :

Post by admin »

This is how the language has been designed. Class B inherits the protected fields and so it can access the inherited field through its own reference (because B has that field). But when you try to access A.i from class B, it fails because B does not have A's i. class B is not involved in the implementation of class A. class B is involved only in the implementation of class B (or its subclasses), so it can access its own fields including the ones that it inherited.


When both the class are in the same package, B can access A.i because protected is a lower protection level than pacakge and since any class in the same package can access A.i, B can also access it. The fact that B is a subclass of A is irrelevant in this case.

HTH,
Paul.
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stessy
Posts: 7
Joined: Sat Nov 12, 2011 5:38 am
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Re: About Question com.enthuware.ets.scjp.v6.2.455 :

Post by stessy »

I thought that protected was higher than default access and protected could only be used for subclassing. That's the reason why I hadn't understood.

public --> protected --> default --> private

Thanks for this clarification.

PMiglani
Posts: 14
Joined: Sat Jan 19, 2013 8:42 am
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Re: About Question com.enthuware.ets.scjp.v6.2.455 :

Post by PMiglani »

Hi,

I am not clear about the output of following program


class A
{
public int i = 15;
public int getI() { return i; }
}


public class B extends A
{
int i=8;
public void process(A a)
{
a.i = a.i*2;
i=i*3;
}
public static void main(String[] args)
{
A a = new B();
B b = new B();

b.process(a);


System.out.println( a.getI() );
System.out.println( a.i );
System.out.println( b.i );
System.out.println( b.getI() );
}
}


Output :-

30
30
24
15

Why b.getI() is displaying 15 ??

Thanks
Puneet

pushpull
Posts: 14
Joined: Thu May 14, 2015 3:25 pm
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Re: About Question com.enthuware.ets.scjp.v6.2.455 :

Post by pushpull »

PMiglani wrote: Why b.getI() is displaying 15 ??
Because class B does not override the method getI()

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