Jess will call Fact.equals() to evaluate the first rule -- if Fact
doesn't override equals(), then of course Object's version is used,
which is based on identity. Jess may also call Fact.hashCode() as part
of computing a hashcode for the jess.Fact objects.
On Jul 12, 2010, at 4:56 AM, Henrique Lopes Cardoso wrote:
Hi,
I have 2 deftemplates, each of which includes a slot with a Java
object.
I want to have a rule that fires when the objects inside those slots
are
equal. This is my implementation:
(deftemplate t1 (slot o))
(deftemplate t2 (slot o))
(defrule r1
(t1 (o ?obj))
(t2 (o ?obj))
=>
(printout t "--r1--->" (call ?obj getX) crlf) )
(defrule r2
(t1 (o ?obj1))
(t2 (o ?obj2))
(test (= (call ?obj1 equals ?obj2) TRUE))
=>
(printout t "--r2--->" (call ?obj1 getX) crlf) )
(reset)
(assert (t1 (o (new Fact 1))))
(assert (t2 (o (new Fact 1))))
(facts)
(run)
As can be easily seen, my Fact class has an x attribute accessible via
getX(). I have also implemented equals().
Rule r2 works fine.
I was just trying to better understand the contents of section 8.4 of
the manual, where it is said that "Jess may call the equals and
hashCode
methods of any objects in working memory". This does not mean that
rule
r1 should fire, right? Rule r1 really demands for the references to
refer to the same object, not equal objects, am I right?
So, in this case should I implement hashCode()? It does not seem to be
necessary. Is it crucial only when using shadow facts?
Thanks.
Henrique
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Ernest Friedman-Hill
Informatics & Decision Sciences, Sandia National Laboratories
PO Box 969, MS 9012, Livermore, CA 94550
http://www.jessrules.com
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