Trouble with access modifier protected

[Fergus Flanagan]

I'm learning about access modifiers and Protected is doing my head in. I thought I understood it but I can't get the following code to work. Before I go crazy can someone tell me what I'm doing wrong here please.

From my understanding a protected modifier is similar to default with the addition that it can also be accessed in another package via the use of a subclass......Is this correct?

package cop;
public class Main {
	public static void main(String[] args) {
	}
}


package cop;
public class AnotherClass {
	protected String prot = "Protected"; 
}


package anotherPkg;
import cop.*;
public class AnotherClassInAnotherPkg extends AnotherClass {
	public void runMe() {
		AnotherClass ac = new AnotherClass();
		System.out.println(ac.prot);    //ERROR HERE: The field AnotherClass.prot is not visible ????????
	}
}

[Henry Wong]

Fergus Flanagan wrote:From my understanding a protected modifier is similar to default with the addition that it can also be accessed in another package via the use of a subclass......Is this correct?

Yes.

Fergus Flanagan wrote:

		System.out.println(ac.prot);    //ERROR HERE: The field AnotherClass.prot is not visible ????????

You forgot about the "responsible for the implementation" requirement.

http://docs.oracle.com/javase/specs/jls/se8/html/jls-6.html#jls-6.6.2

In this case, since the accessing code is from the AnotherClassInAnotherPkg class, the instance type must be IS-A AnotherClassInAnotherPkg instance.

Henry

[Fergus Flanagan]

Okay see my mistake not sure I fully understand it, it sort of makes sense. The point of extending the class is for increased functionality in the new objects which inherit from the parent class. I was using the parent objects when I should have been using the child objects.

the instance type must be IS-A AnotherClassInAnotherPkg instance.

What does "IS-A" mean?

[Knute Snortum]

Fergus Flanagan wrote:What does "IS-A" mean?

Say you have a class Animal and you want to create a subclass Dog. Does this pass the IS-A test? "A dog IS-A animal". Yes, so the subclass makes sense.

[Fergus Flanagan]

Okay thank you.

[Campbell Ritchie]

Welcome to the Ranch

You will see things like
public class Car extends Vehicle
because a Car ”IS‑A“ Vehicle. It is one of the rules of inheritance.
You should never see things like
public class Car extends Wheel
because a Car ”IS‑NOT‑A“ Wheel.
When you learn about composition and aggregation you will find that
a Car ”HAS‑A“ Wheel. (Well, usually several wheels.)

The code which can access protected members must be able to say it is an instance of a subclass, whether in the same package or in a different package. It does cause quite a bit of confusion to lots of people.

[Fergus Flanagan]

Thank you guys, slowly making sense

[Campbell Ritchie]

You're welcome We try our hardest and people always say I am trying.