re: JavaMemoryModel: final, pseudo-final and write protected fields

From: Doug Lea (
Date: Thu Oct 21 1999 - 05:23:08 EDT

I said:

> My take on this is that language/vm treatment of final are too weak.
> I think this code compiles and loads due to limitations in the
> compile/verify checks, not by any other intent. Probably the best
> solution would be to fix the compiler and verifier (and their specs)
> to be more conservative here, outlawing all potential reads before
> writes of finals -- which would in particular disallow all non-static
> method calls on this before values are set.

Oh, now I remember these issues.

If you conservatively disallow all method calls (and other uses of
"this") before final assignments in constructors, then a lot of
subclass constructors become illegal. For example, without full static
analysis, you'd have to disallow the innocuous:

class Super {
   Super() { f(); }
   void f() { System.out.println("Hi!"); }

class X extends Super {
  final int field;
  X(int i) {
    field = i;

People would not be very happy about this.

Still, it seems like a bad idea to establish any sort of guarantees in
cases where people misuse finals. A disclaimer saying that all bets
are off if the non-assigned value of a final is ever accessed sounds
reasonable to me. Better static analysis tools could help programmers
avoid such cases.

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