Dan's Study Guide exam Ch-4 - Overriding static method question

[shweta mathur]

Hi Dan,
This is regarding
Ch-4 Declarations & Access Control
Set 1 - Question 8
It says that the following statement is true

a. If the superclass method is static, then the overriding method must also be static.

But Section 6.2 Pg 181 of Khalid Mughal says that

Any final,static & private methods in a class cannot be overridden.

Is the following method overriding, hiding or something else ?

 class Test4Super{
static void m1(){
System.out.println("Test4Super.m1()");
};
}
class Test4 extends Test4Super{
static void m1(){
System.out.println("Test4.m1()");
}
public static void main(String args[]){
Test4Super obj = new Test4();
obj.m1();
Test4Super obj0 = (Test4Super)obj;
obj0.m1();
Test4 obj00 = (Test4)obj;
obj00.m1();
Test4 obj1 = new Test4();
obj1.m1();
}
} 

o/p
Test4Super.m1()
Test4Super.m1()
Test4.m1()
Test4.m1()

[Alfred Kemety]

Static methods are not overriden, they are hidden. Final methods can't be neither hidden or overriden. Private methods are not inherited in the first place to be hidden or overriden, you can declare methods with the same signature as the private methods in the subclass with no problem.
The "overriden" in the first quote refers to hidding it. A non-static method in a subclass can't have the same signature as a static method in the superclass and vice-versa.
HTH

[Dan Chisholm]

In the next version of the exam that answer option will be changed to the following.

If the superclass method is static, then any method with the same signature in a subclass must also be static.

[shweta mathur]

Thanks Alfred & Dan !

[Timothy Toe]

Static methods are not overriden, they are hidden. Final methods can't be neither hidden or overriden. Private methods are not inherited in the first place to be hidden or overriden, you can declare methods with the same signature as the private methods in the subclass with no problem.

I am not clear of the difference between
1) overriding
2) hiding and
3) inherit
And also, what do you mean by "same signature" ? method name + parameter type list ? Is the return type of the method included ? No right ? Anything else ?

Any explanation is greatly appreciated.
[ November 22, 2002: Message edited by: Ioow Gneb ]

[shweta mathur]

The signature of a method consists of the name of the method and the number and types of formal parameters to the method.
Ref Section 8.4.2 of JLS for method signature.
Section 8.4.6 of JLS will be helpful in knowing the differences b/w inheritance, overriding & hiding.
1) Inheritance - In a class all the non-private methods that are accessible to code from its direct superclass and direct superinterfaces are said to be inherited.
For inheriting the the method of a superclass the class shud not override or hide that method.
2) A method m1 of the class is said to be overridden if the subclass defines a method m1 with the same signature as the superclass's m1.
Overriding is only for instance methods and not for static methods.
3) A method m2 of the class is said to be hidden if m2 is static & the subclass defines a static method m2 with the same signature as the superclass's m2.Hiding is by Static (class methods)