Fwd: inner class reading uninitialized value from outer class

[Jonathan Gibbons]

As the owner of the compiler-dev list, I'm forwarding this email that 
was bounced here from the jls-jvms-spec-comments at openjdk.java.net list.

-- Jon

On 06/22/2016 04:54 PM, compiler-dev-owner at openjdk.java.net wrote:
> Subject:
> inner class reading uninitialized value from outer class
> From:
> Xen <list at xenhideout.nl>
> Date:
> 06/05/2016 07:10 AM
>
> To:
> jls-jvms-spec-comments at openjdk.java.net
>
>
> I am not sure if this is the proper list to discuss a thing like this.
>
> The only alternative I have really found thus far is compiler-dev.
>
>
> I created an inner class that reads a value from the outer class:
>
>
> class Outer {
>   final int value;
>
>   Outer() {
>     value = 1;
>   }
>
>   class Inner {
>     int mine = Outer.this.value;
>   }
> }
>
> Now an instance of inner is created before the constructor of outer is 
> called.
>
> The OpenJDK 8 compiler gives no error, but the value that is getting 
> read is 0; even though it has not been initialized (no oddity here) 
> but it is getting read even though it is not initialized; and there is 
> no compiler warning saying so:
>
> class Outer {
>   Inner haha = new Inner(); // gets initialized to 0, not to 1
>
>   ...
> }
>
> However if we put the creation into the constructor of outer, it gets 
> the proper value. So there are 2 init stages: before the constructor 
> is called, and after. You can call both inner class pre-init and 
> constructor (both instanced) before the outer class constructor has 
> been called.
>
> Nothing odd here, but it does read a final value that has not been 
> initialized yet. Maybe this should simply be a compiler error. I don't 
> know what the spec says about this. It will just compile fine on 
> openjdk 8 (I got a package error trying to install 9 on my system, 
> hence I am using 8 for (this) now).
>
> Basically I wonder if the spec allows this, or whether this is a 
> compiler error.

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