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Message:

Initialize your variable before using it...

Posted by Kishori Sharan on January 05, 2001 at 9:26 AM

Your program cannot compile because using algorithm of definitive assignment Java makes sure at compile time that each variable which is being used has been initialized ( I mean has a value. Note that I am saying each variable used. It means you can declare a variable but when you try to use its value then only it is a problem if you haven't assigned any value to it or it has not been implicitly assigned a value as in case of instance variable. ) . You just declared a reference variable "a" of type one as in
one a ;
but you didn't put any reference in "a" before using it in th.display(a). You need to do something like
one a = new two ( ) ;
OR
one a = new three ( ) ;
and then it will work.

If you don;t want to do that then just to compile your program you can just declare one a ; as the instance variable of class three ( here you will have to declare static one a ; because you are using it in main ( ) method which is static ). Becuase each reference instance/class variables are initialized to null by default your program will compile but in display method it will throw NullPOinterException.

static void main(String args[]){
three th= new three();
one a;
th.display(a);
}
}