CODEWITHSUNDEEP
javainheritancestatic
G.S
G.S

Reputation: 10871

static variables in inheritance

public class A 
{
    public static int i;
}
public class B extends A
{
    public static void main(String[] args)
    {
        System.out.println("print i=" + B.i); // referred to A.i
    }
}

My question here is how B.i is referred to the A.i?

If the static variable i is inherited why java allows to define another variable i in B class also?

Upvotes: 0

Views: 6760

Answers (4)

Tazo
Tazo

Reputation: 197

i here is a static variable.A static variable,in layman terms,means a single copy being accessed by all classes.So,since your class B extends A,B has an access to the static variable of A.

If you define the variable locally,then the local value of the variable hides the parent class value.

Upvotes: 1

Menelaos
Menelaos

Reputation: 25727

Java allows you to change the specific variable value for the extended class.

This is because, static variables are shared between all objects of the same class. It is a variable which belongs to the class and not to object(instance).

So, when extending the static variables of the parent class are not actually part of the extended class BUT are accessible (as long as they were not private).

Additionally, this can be used to do things such as:

  • using different STATIC CONSTANT for extended classes.

A use for this is to identify classes based on a STATIC integer as apposed to utilizing instanceof. This can be further combined with a switch to change behavior based on an objects type.

So, in the most basic example imagine we want to create a variable represent TYPE.

class A
{
    public static final int NODE_TYPE = NODE_PERSON;
    public static final int NODE_PERSON = 0;
    public static final int NODE_CAR = 1;

}

class B extends Class A
{
    public static int NODE_TYPE = NODE_CAR;
}

This has been used in many frameworks including Eclipse Abstract Syntax Trees:

http://help.eclipse.org/indigo/index.jsp?topic=%2Forg.eclipse.jdt.doc.isv%2Freference%2Fapi%2Forg%2Feclipse%2Fjdt%2Fcore%2Fdom%2FASTNode.html

You will see a list of STATIC INTEGERS which represent different Node Types.

Upvotes: 0

NPE
NPE

Reputation: 500177

A public or protected member of A is visible in all subclasses of A.

If the static variable i is inherited why java allows to define another variable i in B class also?

It's hard to speculate as to why. One possible reason is that this allows one to add members to a base class without breaking any derived classes that already happen to have a member with the same name.

Note that, if you define another i in B, it will shadow A.i, making it difficult to access the latter. I've seen people expecting this to behave polymorphically, but it doesn't (your case is slightly different anyway, since A.i is static).

Upvotes: 1

Ankit
Ankit

Reputation: 6622

there are 2 different things, scope and visibility. you can not redefine a variable in same scope twice (though you can redefine them in nested scopes).

But in case of inheritance, the subclass is out of scope of superclass, but yet has the visibility to that variable because of inheritance. So sub class allows you to define variable i again, though it will hide super class's variable. you wont be able to see its value. (unless used any getter from superclass)

Upvotes: 0

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