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

From: Doug Lea (
Date: Wed Oct 20 1999 - 18:36:19 EDT

> public class A {
> final int x;
> static A I(A a) { return a; }
> A() {
> A a = I(this);
> int i = a.x;
> this.x = 42;
> int j = a.x;
> }
> }
> In looking at the constructor for A, it seems that
> we should be able to replace the second read of a.x
> with a reuse of the previous loaded value; after all,
> a.x is final and cannot change.
> But of course, in this case, it can.

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.

Doug Lea, Computer Science Department, SUNY Oswego, Oswego, NY 13126 USA 315-341-2688 FAX:315-341-5424  
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