inhertence of abstract ()

[Netty poestel]

 
 
abstract class Bang
{
 //abstract void f();  //(0)
   final    void g(){}
 //final    void h(){} //(1)
   protected static int i;
   private int j;
}
final class BigBang extends Bang
{
 //BigBang(int n) { m = n } //(2)
   public static void main(String args[])
   {
      Bang mc = new BigBang();
   }
   void h(){}
 //void k(){ i++; } //(3)
 //void l(){ j++; } //(4)
   int m;
}
 

Question is :-Given the following source code, which of the lines that are commented out may be reinserted without introducing errors?

one of the factors given in the explanation is:-

abstract void f( ) ; //(0)
"If this line is inserted, then class BigBang will have to be declared abstract. "

Is this a fact , that if a class extends a class with a abstract (),it must itself be declared abstract ?

[Barry Gaunt]

If you uncomment that line (//0) there is no implementation of the method in class Bang. So BigBang would have to implement it. But BigBang does not, so BigBang has to be declared abstract. But then we have a contradiction: BigBang is final and cannot be declared abstract! The final prevents BigBang being extended and method f from being provided with an implementation.

[Netty poestel]

Thx. Barry.
this was my cue [qoute] "So BigBang would have to implement it"

[Mike Gershman]

There are actually two issues with uncommenting this line. Do you see them both?

//BigBang(int n) { m = n } //(2)

[Netty poestel]

Yes I do see that it'll no longer have a def. constructor that's used in the main().
Thx

[Pavan Kumat]

Can uncomment following line without any problems -
//void k(){ i++; } //(3)

Can-not uncomment following line since ; is missing -
//BigBang(int n) { m = n } //(2)