Subclass is not initialized...why?

[jay akhawri]

Hi all,

This is possibly something which can be guessed easily...but i hope posting it here could bring more light on it..the situation is explained as follows;



class A { static int a = 1000; }

class B extends A {
static { System.out.print("B "); }
}

class Test {
public static void main(String[] args) {
System.out.println(B.a);
}
}


>> Now this prints 1000

>> But does B was initialized at all???

>> Why?

Have a good day
- Jay

[Ernest Friedman-Hill]

Variables are not polymorphic. The compiler knows when it compiles class "Test" that the variable you've called B.a is really A.a -- class B is not needed to obtain its value. So a reference to A.a is compiled into Test.class, not B.a, and therefore B isn't loaded.

[jay akhawri]

Hi jess,

okey that make sense...but when classloader loads the Test.class in the VM , does it not also load the symbol table? and all the symbols are put in the symbol table at load time?.....does this mean the Linking process only take cares of such situations.....does that also mean Initialization only occures when Linking is done completly.....but what will be the case with Dynamic initialization?

Thanx
- Jay

[Ernest Friedman-Hill]

"Jess?"

When a class is being loaded, yes, its "symbol table" (actually called the constant pool) is loaded, and entries in it that point to other classes cause those other classes to be loaded, too. In this case, class A will be loaded, because class Test will (as I tried to explain) contain a reference to class A, but not to class B, because the "real name" of B.a is actually A.a .

[jay akhawri]

Hi Mr. Hill,

sorry for naming u wrong ..i had in mind that u wrote that book and i wrote that in mistake..i hope you wont mind.

Another of my doubts is that in the case discussed above envolves static linking...but if it were a dynamic linking ..wud compiler had to initialize all classes in VM, even if a subclass entity re-refers an already referred entity by superclass. what wud be flow of execution in that condition?

Have a nice day
- Jay