Access Modifiers Effect on Static Method Hiding Question

I am studying for my SCJP exam and have come across a question that I do not understand and have not yet found a satisfactory explanation.
Given:
package staticExtend;
public class A{
     private String runNow(){
          return "High";
     static class B extends A{
          public String runNow(){
               return "Low";
     public static void main(String args[]){
          A[] a=new B[]{new B(),new C()};
          for(A aa:a)
               System.out.print(aa.runNow()+" ");
class C extends A.B{
     public String runNow(){
          return "Out";
}The output is "High High". The explanation in the sample exam from ExamLab was that because the runNow() method in A was private that only an explicit cast to the B class would invoke the runNow() method in B. I have verified that that is the case, but am not clear on how the runNow() method being declared static in B and how the private access modifier in A results in this behaviour.
Any additional explanation would be greatly appreciated.
Thanks in advance.
-- Ryan

Ryan_Chapin wrote:
OK, so since runNow() in A is private the compiler determines that regardless of the available methods in any of it's sub classes that since we declared the original array reference as "A" that it will invoke the runNow() in A. It's also due to the fact that the invocation came from within A. You would have gotten a compile time error if you tried to place the code in the main method in another class.
>
My mistake about the second part that you mention. You are correct. runNow() in B is NOT static, but the class is static. I guess that was the red herring in this question I don't see how that is related. I actually think that the "red herring" was what I described above. The fact that the code was placed in A, and that private methods can't be overridden.
and the fact that the class itself is static has nothing to do with the behaviour that is being illustrated. Is that correct?Correct

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My question is can static methods be overridden ?
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I filed a bug report on it. I don't know if it's expected behaviour or not, but I expect the compiler to complain if you add @Override to a static method (since it can't be overridden)
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Exception in thread "main" java.lang.Error: Unresolved compilation problem:
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So can we say that Java does not allow static method to be overridden but does not display a compile/run time error when this is done ?
Is this a bug as stated by kajbj ?
Please let me know if i am not clear.If this question has been answered somewhere else in this forum,kindly let me know.
Thank you for your consideration.

amtidumpti wrote:
My question is can static methods be overridden ?
I found this thread [Can Static Method be overridden ?|http://forums.sun.com/thread.jspa?threadID=644752&start=0&tstart=0] .Since it was too old,i have created this new thread.
According to that thread discussion, Java language states that static methods cannot be overridden.
To which kajbj posted a program which did allow overriding of static methods.To quote him :
I filed a bug report on it. I don't know if it's expected behaviour or not, but I expect the compiler to complain if you add @Override to a static method (since it can't be overridden)
/Kaj
Sigh! Amti, are you being misleading on purpose? Kaj did not "post a program which did allow overriding of static methods." He posted a program which used the annotation @Override on a static method, like this:
class A {
    public static void m() {}
class B extends A {
    @Override public static void m() {}
}He wondered why it didn't generate an error message. Well, it does now:
A.java:6: method does not override or implement a method from a supertype
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    ^
1 error

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ashkan.ekhtiari wrote:
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(not)
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mycoffee wrote:
gcameo wrote:
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nikkj wrote:
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cs.student wrote:
Hey guys i just have two questions about two methods used in many controllers/servlets in my app:
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Static methods in data access classes

Are we getting any advantage by keeping functions of DAOs (to be accessed by Session Beans) static ?

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Hello Morten
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Hi,
This seems like a silly quesion but i am trying to access a static method but it tells me that i cant.
The method i am calling from is not static
Thanks

syntax: class name dot static method name (assuming the method is accessible): StaticMethodClassName.aStaticMethod();
can't reference a class member (variable, object, method, ...) from a static method because a static method is not a class member (it is simply a method whose scope is confined to that of the class in which it is defined).
example:
class Foo
int i;
public static void hasSyntaxErr() // this method is not a member of Foo
i = 0; // not allowed because i is a member of Foo
class Fooo
void testStatic() { Foo.hasSyntaxErr(); }
}

When a static method is accessed concurrently

When a static method is accessed by many objects symultaneously(concurrently),
What is happened in the static method.
Are the stacks for that method maded seperately and
each stack doesn't influence other stacks?
thank you in advance.

The static objects or methods concept is clear, one
instance for all objects.No. One instance for the class.
, and every
one know that, static methods is slower than
nonstatic, Since when? I've certainly never heard that before... Do you have a reference I can look at?
and this is as i thought because static
methods are syncronized by default.Absoloutely not!
All synchronization locks on an object. When you synchronize an instance method, it locks on the implicit "this"; When you synchronize a static method, it locks on the class's associated Class object.
So two synchronized static methods in the same class can not be called at the same time, but synchronized instance methods that access static variables can all access those variables at the same time and potentially cause threading problems. In this situation you can declare the static fields volatile or wrap synchronized blocks around all code that accesses them, and synchronize on the same object (perhaps the Class object associated with the current class would be appropriate, but that reallt depends on the rest of your design).

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There does not appear to be anyway to access the Class object from instead a static method.
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class test {
static void printClassName() {
System.out.println( getClass().getName() );

The idea was to have a static method that could be
used to make a lookup based on the classname. Being
able to access the class name would mean that I would
not have to reimplement for every subclass !!!!!Hmm.. what are you trying to look up? Some kind of class-specific constant information maybe?
In general your best bet is to define an abstract method in your parent class for return of the constant value, then define a specific method in each sub-class that overrides it, retrurning the appropriate value.
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Access Modifiers Effect on Static Method Hiding Question

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