Overriding static / non static methods

[Giselle Dazzi]

I came across the following question:
Which of the following statements are true:
A. A static method may be overriden by a static method.
B. A static method may be overriden by a non-static method
C. A non-static method may be overriden by a static method
D. A non-static method may be overriden by a final non-static method.
The answer is D.
I agree D is true.
But since the only info I leaned about this from the book Im reading is that
"A static method may not be overriden to be non-static " , I could not understand why options
A and C are false.... ???

[Corey McGlone]

A static method can not take part in overriding. Overriding is for instance methods only. From the JLS, §8.4.6 Inheritance, Overriding, and Hiding:

A compile-time error occurs if an instance method overrides a static method.
...
A compile-time error occurs if a static method hides an instance method.

That's why those answers are incorrect.
I hope that helps,
Corey

[Giselle Dazzi]

Thanks Corey.
The sad part is that the book Im reading to prepare for the test never mentioned that.
Also I was misled because a static method being overriden by a static method does not cause a compilation error...

[Vince Hon]

Option A.
A static method may be overriden by a static method.
/*
There is only "hiding " of static method instead of overriding
*/
try it:

  
class A {
  static void m1() {
System.out.println(" This is A.m1() ");
}
}
class B extends A {
  static void m1() {
System.out.println(" This is B.m1() ");
}

public static void main (String args[]) {
A a = new B();
B b = new B();

a.m1();
b.m1();
}
}

// the result is
This is A.m1()
This is B.m1()
If overriding occur, the result will be
This is B.m1();
This is B.m1();
Therefore, there will be no overriding of preceding code.
Pls noted that hiding of method means the which method is invoked is determined by the reference type but not the underlying object.
hope this can help

[Wilson Mui]

but does that mean a static method can hide another static method. I guess my concern is about compiling. It sounds to me like it would compile, but with static methods, we are just using the wrong terminology, it is not being overriden it is being hidden. Is that correct?

[Thomas Paul]

Originally posted by Wilson Mui:
but does that mean a static method can hide another static method. I guess my concern is about compiling. It sounds to me like it would compile, but with static methods, we are just using the wrong terminology, it is not being overriden it is being hidden. Is that correct?

Yes, that is correct. Overriding always implies polymorphism and static methods are not polymorphic.

[Giselle Dazzi]

So calls to static methods will be determined at Compilation time just like it happens to overloaded methods ?
btw, that makes me wonder, any special comments about private methods ?

[Wilson Mui]

well I actually asked that couple of days ago. Private methods are in a sense, well are, hidden from any subclass. So if the subclass decides to declare a method with the same name, return type, and parameters, that is fine. It is not considered overloading. I believe even if you declare a method
private [static] final, it can still be redeclared in the subclass. Because the method is, in a very literal sense hidden. So the final modifier isn't violated, because it is not being overriden, and the static modifier isn't being violated (even if the subclass' redeclared method is not static) because it is hidden. Does that make sense.
Can somebody correct me if I'm wrong? Like I said, I just learned this a couple of days ago too.

[Dan Chisholm]

Originally posted by Wilson Mui:
Private methods are in a sense, well are, hidden from any subclass.

The Java Language Specification assigns a very specific meaning to the term "hidden" so it is better to avoid using it for anything beyond that specified by the JLS. It is more correct to say that a private method is not accessible.