static block and static final / non final variables

[anagha patankar]

Here is an example :

 
public class Ex1a {
 
public  Ex1a(){
System.out.println("Hello - in constructor ");
}
 
static{
System.out.println("Inside the static block");
}


public static  [B]final [/B]String finalStr = "UTF-8";



public static String xyz = getData();


public static String getData(){
System.out.println("this method gets invoked");
return "test";
}

public static void main(String args[]){
System.out.println(finalStr);
}

}

The output that I get is : the static block DOES NOT get executed
and variable "finalStr" value = "UTF-8" is displayed

However the same code when executed and changing the variable :

 public static  final String finalStr = "UTF-8";
to :
//no longer a final variable
public static  String finalStr = "UTF-8";
   

Now the output is quite different :

1 >static block gets executed first
2 >variable "xyz" gets initialised - as a result method - "getData()" gets invoked

3 >finally variable "finalStr" value = "UTF-8" is displayed

Obviously this means that final variables behave differently / or are stored separately ?

Question being why are final variables initialised / without the static block being executed ?

My incorrect understanding was any reference to this class ( member variables / methods ) would cause the static block to be executed .

Could someone explain this behaviour ?

Regards ,
-anagha

[Jim Yingst]

[anagha]: My incorrect understanding was any reference to this class ( member variables / methods ) would cause the static block to be executed .

Almost. There's an exception if the field is a constant variable. See these JLS links:

When Initialization Occurs
constant variable

Using final the way you did makes the variable into a compile-time constant expression, which means at run time there's no need to load the class that originally defined it.
[ October 14, 2006: Message edited by: Jim Yingst ]

[Bauke Scholtz]

I cannot reproduce this problem? Neither in Java 1.4.2 as Java 1.5.0.

In both cases (finalStr being final or not) I get the output from static initializer block, the getData method and finally the value of finalStr.

[Burkhard Hassel]

Bauke Scholtz posted October 14, 2006 04:48 AM:

I cannot reproduce this problem? Neither in Java 1.4.2 as Java 1.5.0.

Me too, neither on the original compiler nor on the compiler provided with Eclipse 3.1

[Jim Yingst]

Yes, evidently anagha didn't give us the correct code here. The problem described can be witnessed if the finalStr field is referenced from outside the class that defines it, e.g.

public class Test {
    public static void main(String[] args) {
        System.out.println(Ex1a.finalStr);
    }
}

[Burkhard Hassel]

I see Jim, I didn't know this exception.
Yes, yes, the language specification...
always worth a look!

Yours,
Bu.

[anagha patankar]

Hello Jim ,
My apologies for the incorrect example .

As you have correctly pointed out the call was being made from outside the class and not from within .

Thanks for the pointers and once again I sincerely apologise for creating confusion with the incorrect example .

Regards ,
-anagha