From dougo@ccs.neu.edu  Sat Dec 16 01:44:59 2000
X-UIDL: bb7bc5e49a1da7c1ed1b46efa8b6a54c
Return-Path: <dougo@ccs.neu.edu>
Received: from vega.ccs.neu.edu (dougo@vega.ccs.neu.edu [129.10.116.206])
	by amber.ccs.neu.edu (8.10.0.Beta10/8.10.0.Beta10) with ESMTP id eBG6ivX14926;
	Sat, 16 Dec 2000 01:44:57 -0500 (EST)
Received: (from dougo@localhost)
	by vega.ccs.neu.edu (8.10.0.Beta10/8.10.0.Beta10) id eBG6iuE16185;
	Sat, 16 Dec 2000 01:44:56 -0500 (EST)
From: Doug Orleans <dougo@ccs.neu.edu>
Message-ID: <14907.3944.130188.238931@vega.ccs.neu.edu>
Date: Sat, 16 Dec 2000 01:44:56 -0500 (EST)
To: Karl Lieberherr <lieber@ccs.neu.edu>
Cc: avi@ccs.neu.edu, dougo@ccs.neu.edu
Subject: Re: DJ and collection classes
In-Reply-To: <200012151631.eBFGV6301751@gomeisa.ccs.neu.edu>
References: <200012151631.eBFGV6301751@gomeisa.ccs.neu.edu>
X-Mailer: VM 6.72 under 21.1 (patch 3) "Acadia" XEmacs Lucid
X-Face: (4D-osoq?}7M3\EgvbWKo<JkN/8h)A`1b^S1[8/OtYE1A61B!AOmH#YD+{HKhr7}@8gMv~.
	 tsxTzT"g.oP0dTl!q
Mime-Version: 1.0 (generated by tm-edit 7.108)
Content-Type: text/plain; charset=US-ASCII
Content-Length: 1476
Status: RO
X-Status: 
X-Keywords:                 
X-UID: 39

Karl Lieberherr writes:
 > Hi Doug:
 > 
 > /proj/adaptive3/lieber/grading/com3360/avi
 > 
 > Avi and I don't understand why DJ does not traverse 
 > in to the list of emplyees, if
 > we change Vector to the List interface in Main.java and University.java.
 > 
 > Is this a bug in DJ?
 > We checked class graph and traversal graph and they looked fine.

It's sort of a bug in DJ.  The problem is that if the concrete class
of the object that's a List, e.g. ArrayList, is not in the
TraversalGraph, then the traverse algorithm will stop when it sees the
class that it doesn't know about.  The reason it's not in the
TraversalGraph is that it's not in the ClassGraph!  And the reason
it's not in the ClassGraph is that the ClassGraph is constructed from
the field types, and ArrayList is only referred to in the body of the
method, i.e.

    List employees = new ArrayList();

The field type (of University) is List, so DJ has no way of knowing
that it might run across an ArrayList until it actually does so.  I
could probably fix this by having it check to see, when it runs
into a class that's not in the TraversalGraph, if it's also not in the 
ClassGraph but all its superclasses are okay, then proceed.  (Sorry if 
that doesn't make any sense-- it's just a note to myself.)  I'll try
this when I get back to working on DJ next quarter.

Meanwhile, the workaround is simply to add the class to the ClassGraph
manually:

		cg.addClass(ArrayList.class, false, false);

--Doug