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final instance variable

sweety sinha
Ranch Hand

Joined: Jul 07, 2008
Posts: 76
public class Logger
{

private static int loggerCount = 0;

private final int logLevel;

private Logger(int logLevel) throws IllegalArgumentException
{
if(logLevel < 0 || logLevel > 10)
{
throw new IllegalArgumentException("logLevel can only take values 0 to 10");
}
this.logLevel = logLevel;
}

public static Logger createInstance(int logLevel)
{
Logger retObj = null;
try
{
retObj = new Logger(logLevel);
}
finally
{
loggerCount++;
}
return retObj;
}

}

how it is working ???
as we know that final member variable of type int has no default value , it need to be explicitly assigned the value at the time of declaration or in the constructor of the class.

correct me if i am wrong
Ulf Dittmer
Marshal

Joined: Mar 22, 2005
Posts: 42933
    
  68
or in the constructor of the class

Isn't that exactly what's happening?
Przemek Malirz
Greenhorn

Joined: Sep 02, 2008
Posts: 11
Inside Logger constructor:

this.logLevel = logLevel;


SCJP 6.0 (87%)
Ashu Jain
Ranch Hand

Joined: Feb 24, 2008
Posts: 73
Hi,

Golden rule regarding default values of fields is::

If no intialization is provided for an instance variable either in the declaration or in constructor or in instance initiatlizer block then it is automatically initialized with the default value of its type when the class is instantiated.

So in above program, the instance variable is initialized with default value = 0.(int default value)

I hope that explains.

Ashu
- SCJP 1.4
ankit kumar
Ranch Hand

Joined: Apr 28, 2008
Posts: 108
private Logger(int logLevel) throws IllegalArgumentException
{
if(logLevel < 0 || logLevel > 10)
{
throw new IllegalArgumentException("logLevel can only take values 0 to 10");
}
this.logLevel = logLevel;
}


In this constructor you are assiging the value to the logLevel . before this you are not using it thats why is not giving you the error otherwise it will give you the error The blank final field logLevel may not have been initialized


Cleared SCJP 1.5 | Cleared SCWCD 5.0
SCDJWS 6 in progress.....
sweety sinha
Ranch Hand

Joined: Jul 07, 2008
Posts: 76
thanks guys, i didn't read it correctly
Arun Krishnan Nair
Greenhorn

Joined: Aug 14, 2008
Posts: 18
Why the variable logLevel is declared as final?


SCJP 5 - 100%
Aiming for SCBCD 5 & SCWCD 5
geet kaur
Ranch Hand

Joined: Sep 03, 2008
Posts: 78
hi....
i just faced the same problem of declaring final variables...
we have to initiaze at the same time as well as the same line where it is declared..otherwise it eill give the compiler error...the variable might not have been initialised....
Ankit Garg
Sheriff

Joined: Aug 03, 2008
Posts: 9321
    
  17

Even when you initialize a final constant at the time of declaration, you have to initialize it with another compile time constant or literal to make it a compile time constant.

int a = 10;
final int b = a;//not a compile time constant....


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