Calls to inner class super constructor and putfield

Gordon Syme gordon at
Fri Sep 25 05:35:51 PDT 2009

On Thu, 2009-09-24 at 10:18 -0700, John Rose wrote:
> On Sep 23, 2009, at 3:38 AM, Gordon Syme wrote:
> > I have noticed that when an inner class is compiled the call to store
> > the outer class instance reference in the synthetic 'this$n' field
> > occurs before the call to the inner class's super constructor.
> The initialization of uplevel links (e.g., this$0) needs to be done  
> before the superclass constructor call, because the superclass  
> constructor can sometimes call a virtual method on the subclass.  This  
> was an original bug in inner classes, leading to surprising NPEs  
> coming out of uplevel references.  We couldn't fix the bug until the  
> verifier was liberalized slightly (and safely) to allow fields to be  
> initialized before the constructor call.

Thanks for the reply John, that makes a lot of sense. I hadn't even
considered virtual calls from the superclass ctor!

Much appreciated


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