Re: SISC in applets

Turadg Aleahmad wrote:

> I couldn't get this to work.  I put a custom Defaults.class into a 
> sisc-override.jar and put that earlier in the class path.

You are right. It looks like constants (i.e. final variables) cannot be 
overridden this way. I don't know what the JLS says on the matter, but 
it's really odd behaviour.

> BTW, why is 
> it an interface instead of an abstract class?  I read in Effective Java 
> that using interfaces for constants is bad.  You can't argue on brevity 
> since DEFAULT_PERMIT_INTERRUPTS is just as long as 
> Defaults.PERMIT_INTERRUPTS.  Ok, one char shorter.  :)

I don't think it's a big deal. However, due to the above problem I had 
to make Defaults a class anyway (since all vars in interfaces are 
final). Fixed in CVS.


> In other news, I added a target that builds sisc-heap.jar.  This 
> contains sisc/boot/sisc.shp and sisc/boot/HeapAnchor.class.

Can you explain what HeapAnchorClass is for? I've read the comment in 
the file but I still do not understand why we need the class.

> This works 
> fine for me, but I have another idea that may be better:  
> sisc.boot.HeapLoader (or HeapUtil, something like that).  It has one 
> method getHeap() (or whatever) that returns a SeekableInputStream.
> 
> public static SeekableInputStream getHeap() {
>    URL heapURL = this.class.getResource("sisc.shp");
>    if (heapURL == null) return null;
>    return new MemoryRandomAccessInputStream(heapURL.openStream());
> }
> 
> The only problem I see with this is creating Java code that depends on 
> the JAR that ant builds.  But I think it's important for applets to have 
> an easy, consistent way to retrieve the heap and I would say that weighs 
> more.  What do you think?

How an embedded SISC system (applets are just one case of this) locates 
and accesses the heap should be up to the programmer. I dislike the idea 
of having code in the SISC core that makes as many assumptions as the 
code above, e.g.

* that the heap file is called sisc.shp
* that the heap file is available as a resource
* that the heap file lives under sisc/boot

*none* of these assumptions are true when SISC is run from the command line.


Matthias.




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