final variables initialization

[Li Wenfeng]

When I compile the following code:
class A{
final int i;
}
It generates compiler error: "variable i might not have been initialized"
but,In Brian's SCJP book, it says:

The following code is legal, even though the final variable is not initialized within the same line on which it is declared:
public final int users; // Does not initialize a final variable

also,He said this several times in his book.
What's the truth? I think Brian made a mistake!
thanks!

[sam patel]

Originally posted by Li Wenfeng:
When I compile the following code:
class A{
final int i;
}
It generates compiler error: "variable i might not have been initialized"
but,In Brian's SCJP book, it says:

also,He said this several times in his book.
What's the truth? I think Brian made a mistake!
thanks!

I think Brian made a mistake...
You need to initialize a final variable.....

[Anthony Villanueva]

i is blank final variable. You can initialize it in the constructor:

public class Test33
{
public static void main(String args[])
{
new SomeClass(42).print();
}
}
class SomeClass
{
private final int value;
SomeClass(int i)
{
value = i;
}
void print()
{
System.out.println("Value = " + value);
}
}

[Jack Lau]

Originally posted by Anthony Villanueva:
i is blank final variable. You can initialize it in the constructor:

public class Test33
{
public static void main(String args[])
{
new SomeClass(42).print();
}
}
class SomeClass
{
private final int value;
SomeClass(int i)
{
value = i;
}
void print()
{
System.out.println("Value = " + value);
}
}

You can declare final member without initialization in one line but it is necessary to initialize it in the constructor.

[Anthony Villanueva]

You can use an initializer block as well...

public class Test33
{
public static void main(String args[])
{
new SomeClass().print();
}
}
class SomeClass
{
private final long value;
{ value = Hat.pull(); }
void print()
{
System.out.println("Value = " + value);
}
}
class Hat
{
static long pull()
{
return Math.round(Math.random()*10);
} 
}

[Meg Adal]

I am not sure but remember of reading somewhere that
"final variable must be initialized before constructor ends(ie controls goes out of constructor)"
So we can initialize it in a block or in contructor
Correct me if I am wrong
Megan

[Barkat Mardhani]

Hi Megan:
I think you are right. If final is a member data field, it has to be initialized at the declaration or in a subsequent initilizer or at most in the constructor. Otherwise, when initialized in some other place, compiler will complain that value can not be assigned to a final variable. Interestingly, if you forget to initialize a final and NEVER use it in your code, it would compile and run fine.
However, if final is method variable, you can initialize it before its first use....
Thanks
Barkat

[Li Wenfeng]

Another thing, you can't initialize a class-level final variable in both the initializer block and constructor.

class FinalVarialbe{
    final int i;
    {
       i=0;
    }
    FinalVariable(){
       i=1; // line 7
    }
}

It will complain about: "variable i might already have been assigned to" in line 7.

[Barkat Mardhani]

I thinks rule about any (class level, method level, within an argument) final variable is that they can be assigned only once.