Interface instant variables

[Henry Zhi Lin]

Another question for you guys, it from John Meyers' mock test.

 class num {
   int x=9;
}
 
interface blob {
   final num n = new num();
   final Integer number = 1;
}
 
class test implements blob {
   
   public static void main (  String [] args ) {
      n.x = 10;    // 1
      number++;    // 2
   }
}   

The code has compilation error on line 2.

My question is why the compilation pass the line 1? n is a final as well?

[Henry Zhi Lin]

Just had another thought, it pass line one because it change the n's object's x value, but does not change reference n to other object (still point to the old object with x changed). Unlike n, number++ change it reference to other primitive object?

Am I right?
[ November 07, 2008: Message edited by: Henry Zhi Lin ]

[Rekha Srinath]

Yes you are right Henry..
Once a value is assigned to a final wrapper object, its value cannot be changed.
See this link for a related post:
https://coderanch.com/t/270629/java-programmer-SCJP/certification/Immutability-Wrapper-Objects

[Henry Zhi Lin]

See you post, and thanks for your explain.