Can abstract class has static member?

[SoonAnn Lim]

Hi,
1. I have two question. Can a static member exist in an abstract class? If yes, why do we do so in general?
2. Can a private method in super class be overwritten in subclass? Thanks a lot.

[Desai Sandeep]

Yes, you may have static member (fields/methods) in an abstarct class.
You can override a private method of the superclass in your subclass.However, the term override doesnot make sense in this context, as the subclass is not inheriting that method.
Hope this helps,
Sandeep

[Kaspar Dahlqvist]

Howdy hoo!
1) Yes. An abstract class can have a static variable. And why we do so? Well, why do we use static variables in general?
2) A private method cannot be overridden in any subclass. Even so, this is possible:
class A {
private void a() {}
}
class B {
public void a() {}
}
This seems like an override, but a call to super.a() in B.a() would fail. This is because a() is private in A and cannot be seen outside this class, even though B inherits from A. This is how private always works!
a() method in class B is therefore a completely new method, and has not got anything to do with private method a() in class A.
Hope this helps!
/Kaspar

[Ashwin Desai]

Hi,

Static Variables can be used in an abstract class to define constants that could be used througout the class hierarchy.
Ashwin.

[SoonAnn Lim]

Thanks a lot

[Rex Rock]

On the same token,
are private members not inherited or is it they are inherited but are not accessible???

[Jim Yingst]

Ashwin- static members can be used in abstract classes exactly as they can in regular classes. They don't have to be constants.
Rex- I'd say private members are inherited but inaccessible. The data in a private field is there in the JVM object, and if you deserialize the subclass object to a file, you can see the private parent data in the file, but you can't access that data from the child object. But depending on exactly what people mean by "inherited", other people may answer this differently. If a tree falls in a forest and no one is there to hear it, does it make a sound? It depends if you define "sound" as the vibration of air molecules, or the perceptions of such a vibration by a listener. Same problem here - if data is there but you can't use it directly, is it "inherited"?

[Joshua Bloch]

Originally posted by Jim Yingst:

I'd say private members are inherited but inaccessible...

Hi. Private members really aren't inherited (JLS 8.2, P. 148). The JLS defines the term carefully.
Regards,

------------------
Joshua Bloch
Author of Effective Java

[Jim Yingst]

Oops - quite right. Serves me right for bringing in silly philosophy questions.

[SoonAnn Lim]

So, can i make a conclusion that when a method or a member of a class has private modifier, it means the member or method is not modifiable and accessible. Even we can give the same method name in the subclass, this method does not have anything to do with the same method with the same name (with private modifier) in the super class. Am i correct?

[Soham Pawar]

My question is that if we can use private keyword along  static variables and methods inside the Abstract Class, then why it is said that  inside the  Abstract Class we cannot use private keyword ?

[Campbell Ritchie]

Welcome to the Ranch

Who says the keyword private is banned? The JLS prohibits marking a method both private and abstract, but that is different from banning private.
An abstract method must be implemented in subclasses, and a private member of the class isn't inherited, so it can't be implemented in subclasses, so private abstract is a self‑contradictory modifier.

abstract class Foo
{
   private static final int X = 1234567890;
   //...
   public void someMethod()
   {
      /* something using X; */
   }
   // ...
}

The above code shows how you might use a private static field. It is possible, but I don't think I would call it good design.