final modifier in variable

[Anthony Karta]

why final class variable need to be initialized in the same line but it's Not the case for final method variable??
thanks

    
class test0
{   
    //final int x; // must be initialized in the same line
    public static void main( String args[] )
{
final int x; 
 
}
}

[Shailesh Kumar]

final class variable
->can be initialized in the same line
->or in instance initializer
-> or in the constructor

    
class test0
{   
    final int x; //either here
     {
     x = 10; // or here
      }
 
   test0(){
   x=10; // or here
   }
 
    public static void main( String args[] )
{
final int x; 
 
}
}
 

[David Kennedy]

Why am i finding that Anthonys code uncommented does compile in eclipse even
though it does say there is an error?

[Maneessh saxena]

hi anthony,

uninitilized final instance variables(also called as blank final) can stay blank up to descretation of constructor.meant they need not to be initilized
in the same line they are declered but must be initilized before constructor
completes(as they are not provided any default value).

whereas final static vars must be initilized in the same line they are declered in it's mendetory....

hope this will help

Regards
Maneesh Saxena

[marc weber]

Basically...

final instance variables must be valued before the constructor exits -- either at the point of declaration, in an initializer block, or in a constructor. If not explicitly valued by the time the constructor exits, they have a default value of binary zero.

final static variables must be valued with the initialization of the class -- either at the point of declaration or in a static block (see code below). If not explicitly valued, they have a default value of binary zero.

final local variables must be valued at the point of declaration. Because local variables do not get default values, this is the only option. However, an uninitialized local variable won't cause an error until an attempt is made to use its value (see code below).

EDIT: This is not quite right. See correction in post below.

class Finals {
  static final int x; //VALUED IN STATIC BLOCK
  static {
    x = 18;
  }
  public static void main(String[] args) {
    final int y; //OK UNTIL YOU TRY TO READ IT
    System.out.println(x);
  }
}

[ January 10, 2007: Message edited by: marc weber ]

[Anuragk kushwaha]

Hi Weber,

you said

[B]final instance variables [/B]must be valued before the constructor exits -- either at the point of declaration, in an initializer block, or in a constructor. If not explicitly valued by the time the constructor exits, [B]they have a default value of binary zero[/B]
 

then why the below code is not compiled

class test0{    
 final int x; // must be initialized in the same line  
    public static void main( String args[] )
    {
     final int x;  
     
    }
  
}

why not instence var x gets its default value... please reply somone...me confused

[marc weber]

Originally posted by anuragk kushwaha:
...why not instence var x gets its default value...

Sorry, that's my mistake. A non-local final variable must be explicitly valued. It does not use a default value.

[Giri Kanduri]

Hi Here I am adding a small point to this.
If the Final variable is inside the method we need to initialize the value before using that variable, Irrespective of the place.
Please see the below example......

class FinalTest
{
public static void main(String[] args){
final int x;
System.out.println("IN FinalTest");
x=9;
System.out.println(x);

}
}

[Anuragk kushwaha]

now i think the conclusion...

1. when the instense var, class var and local var used without final keyword then instence var and class var get its default value and local var must be initilised otherwise give compilation error.


2.. and when used with final keyword then instence var and static var must be initilised otherwise give compilation error, while local final var may be left uninitilised, it will not give compile time error but if we will be trying to use that local var then it will give compile time error.
----------
this will compile without error

class test0 {
  public static void main (String[] s) {
  [B] final int x;[/B]
}
}

but the following will not compile.........

class test0 {
  public static void main (String[] s) {
  [B] final int x;[/B]
System.out.println(x);   // will not compiled.
 
}
}