static method can be overriden or not

[Sivaguru Natarajan]

hai

i want to clarify one doubt regarding static method.

in K&B Scjp1.6 page no 161 at chapter 2 they specified static method can't be overriden but i executed this below code i got different thing



class A {
// public static void display(){

static void display(){
System.out.println ("Static method of A ");
}

}
class B extends A {

static void display(){

System.out.println ("Static method of B ");
}
}
class Static {
public static void main(String Args[]) {
A a=new A();
B b=new B();
a.display();
b.display();

}
}

output

Static method of A
Static method of B
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


if i write method in A with public specifier like public static void display(){

i am getting compile time error like

Static.java:10: display() in B cannot override display() in A; attempting to assign weaker access privileges; was public
static void display(){


normally the above error comes in overiding instance method trying to assign weaker pevilleges in Sub class if static method can not be able overridden means why the above message is comming

[Brij Garg]

I think the same rule applies for static methods as in case of overriding.
But at the time of calling static methods, they are called on the basis of the type of the reference variable.

[Vyas Sanzgiri]

I am confused with the answer as much as with the question. Can someone clarify?

[Paul Somnath]

There is a difference when you try to override static methods.
They are actually hidden.
See this url for more details.

[sree visu]

Hello every one.You could see the below code snippet which i have modified slightly
the code nippet which Sivagure natarajan have given in the forum

snippet 1

    
 

class A {
// public static void display(){
 
static void display(){
System.out.println ("Static method of A ");
}
 
}
class B extends A {
 
static void display(){
 
System.out.println ("Static method of B ");
}
}
class Static {
public static void main(String Args[]) {
A a=new B();
A b=new A();
B c=new B();
 
B.display(); //Prints static method of B ------------------------ 1
A.display(); //Prints static method of A ------------------------ 2
 
a.display(); //Prints static method of A -------------------------  3
b.display(); //Prints static method of A -------------------------  4
c.display(); //Prints static method of B--------------------------  5
 
}
}
 

You could see that the line 1 and 2 is done using the class reference itself(Since the method A and B)
are static.This is of no wonder.

If this would have been a non static method illustrated by the following snippet

Snippet 2

  
class A {
// public static void display(){
 
void display(){
System.out.println ("Static method of A ");
}
 
}
class B extends A {
 
void display(){
 
System.out.println ("Static method of B ");
}
}
class Static {
public static void main(String Args[]) {
A a=new B();
A b=new A();
B c=new B();
 

 
a.display(); //Prints static method of B -------------------------  1
b.display(); //Prints static method of A -------------------------  2
c.display(); //Prints static method of B--------------------------  3
 
}
}

you could see that the first line in snippet1 must have printed B since this reference points to the constructor of B but since

Static methods could not be overridden

It prints A.I hope this solves the problem and clarifies your doubts.If doubt still persists please feel free to use javaranch

[sree visu]

when i started replying the reply from paul was not there only when i posted i noticed it.His post gives a better explanation i think.Any way have a happy reading...

[vidhya suvarna]

Siva,
what i understand from your code is that when your adding public static void display() you are trying to overload static method display() in class A. So remember for overloading just changing the return type isnt sufficient. Thats why your getting the error.

class A {
// public static void display(){

static void display(){
System.out.println ("Static method of A ");
}

}
class B extends A {

static void display(){

System.out.println ("Static method of B ");
}
}
class Static {
public static void main(String Args[]) {
A a=new A();
B b=new B();
a.display();
b.display();

}
}

[sree visu]

friend vidhya suvarna ,

what i understand from your code is that when your adding public static void display() you are trying to overload static method display() in class A.

You could see clearly i did not point out that also that line which you pointed out is commented.You could see that in the code which i posted..

[Krishna Srinivasan]

static methods cannot be overridden. It can be hidden by the sub class methods.

[chander shivdasani]

Static methods cannot be overridden but they can be redefined in the subclass.

[Stephen Davies]

I think what Chander is referring to is shadowing? When a method isnt overriden (as its not inherited) but a method with the same name in an extending class is declared (or refined)?

[Stephen Davies]

member hunter9000 of the Sun Java Forums states:

The simple answer is that static methods are associated with the class itself, not with an instance of the class/QUOTE]

Thus the method which is called depends on the class you call it on. (unless you refer to it in a static context eg CLASS.method()

I think this helps the situation a bit
[ September 16, 2008: Message edited by: Stephen Davies ]

[Ganeshkumar cheekati]

actually static methods are not overridden.
i am also not getting why there is a compilation error?

can anyone give me clear explanation so that ranchers can clarify this doubt?
[ October 30, 2008: Message edited by: Ganeshkumar cheekati ]