confuse about protected and static

[dx wu]

package package1;
public class A {
protected  int i;
 
}
package package2;
import package1.A;
 
public class B extends A{
public static void main(String[] args){
A aa = new A();
System.out.println(aa.i);  //compile error
}
 
}

and when the code modifyied as following:

package package1;
public class A {
protected  static int i;
 
}
package package2;
import package1.A;
 
public class B extends A{
public static void main(String[] args){
A aa = new A();
System.out.println(aa.i);  //compile successfully
}
 
}

why add the static modifier the code can complile correct?

[Richard Vagner]

The main() method is static and cannot access a nontstatic variable.

[Barry Gaunt]

"wolfoxer java" you habe been asked before to change your displayed name to conform to our JavaRanch Naming Policy.

I request you one last time to change it.
Thanks
-Barry

[Barry Gaunt]

Your second example (with static) is really equivalent to the following:

package package1;
public class A {
protected  static int i;
 
}
package package2;
import package1.A;
 
public class B extends A{
public static void main(String[] args){
A aa = new A();
System.out.println(A.i);  // reference aa replaced by static reference through class  A
}
 
}  

Access is now allowed because class B extends A and i is protected.

[Mike Gershman]

From The Java Programming Language, 3rd Edition:

protected members can also be accessed from a class through object references that are at least the same type as the class - that is, references of the class's type or one of its subtypes

However:

Protected static members can be accessed in any subclass

So you can fix the original code either by making "i" static or by changing "aa" to a B reference as follows: "B aa = new B();"

This is really obscure stuff, but fair game for the exam.

[dx wu]

thanks very much! and Where to download the Java Programming language 3rd Edititon?

[navneet shrivastava]

oOPS! i dont agree on this ..or may be its incomplete :

"Access is now allowed because class B extends A and i is protected."

[Barry Gaunt]

Originally posted by navneet shrivastava:
oOPS! i dont agree on this ..or may be its incomplete :

"Access is now allowed because class B extends A and i is protected."

In what way do you disagree?

[navneet shrivastava]

--------------------

"Access is now allowed because class B extends A and i is protected."

In what way do you disagree?
--------------------

By the defination of "protected" , a protected memeber is accessible to a subclass in the same/different package.

please correct me if u think am wrong

[Fran Kindred]

I see protected within the same package as same behaviour as default access.


However, no access when outside the package with the exception if you subclass a class that has protected members. Moreover, you have access to the protected members when you create an object of the class you used to subclass.

package com.A;
class A{
//protected members here
}
class C{
//protected members here

}

package com.B;
Class B extends A{

public static void main (String []args){

B b = new B();

// b has access to protected members

C c = new C();

// c has no access to protected members
}
}