Hi Joost. No problems re the names... I just think its happening there as its the "extractor" generated class causing it. Any chance you can wrap this up as a unit testable unit so we can try it out and see what/where the cast is happening? Ta, Michael (PS I am offline all week, so don't feel ignored !) On 1/12/07, Joost de Vries < drools(a)ziener.org&gt; wrote: > > Hi Michael, > > The list is defined in terms of the superclass that both classes share. > And the previous and next methods both have the superclass as the return > type. > > So I'd expect > PreventieveInsluitingsTitel(previous==secondPosition [...] > to evaluate to > <instance of superclass> == <instance of subclass> > I'd expect this check to just fail when the objectreferences do not > refer to the same object. Not to cause a classcastexception. > > But the exception is thrown in the consequence part of the rule during > an invocation of modify( )..... > > So I'm not sure why this construction would be wrong and what would be > the right way to do it. > > oh, by the way; sorry for the dutch classnames. That must make the > problem harder to understand. In fact it's about convictions and the > subclasses are types of convictions. > > regards, > > Joost > > 2007/1/12, Michael Neale <michael.neale(a)gmail.com&gt;: > > > > In terms of your problem, it seems to be to do with: > > PreventieveInsluitingsTitel(previous==secondPosition > > the secondPosition is not a compatible class with previous? > > > > I don't have any specific thoughts on computing a sequence in rules, > > unfortunately... maybe someone else does ? ;) > > > > > > > > > > On 1/11/07, Joost de Vries < drools(a)ziener.org&gt; wrote: > > > > > Hi, > > > > > > I'm new to jBoss Rules and I'm hitting a few snags. I appreciate > > > your insight. > > > > > > Among other things I want to use business rules to compute the right > > > sequence of actions that conforms to legal business rules. > > > The only way I could think of to implement this using rules is to > > > use rewriting production rules similar to: > > > input: ACCAAAC > > > rule: CA -> AC > > > > > > My first question is: what other ways are there to compute a > > > sequence that conforms to sequencing business rules? > > > > > > My second question concerns the nullpointerexceptions and > > > classcastexceptions I'm encountering in my rules. > > > I've got a sequence of C's who are either B's or A's. I.e. C is the > > > common superclass. This superclass has the methods: > > > > > > public C getPrevious(); > > > public C getNext(); > > > > > > Actually it's in dutch so it's > > > > > > public class Straf extends InsluitingsTitel {} > > > and > > > public class PreventieveInsluitingsTitel extends InsluitingsTitel {} > > > > > > and > > > public abstract class InsluitingsTitel{ > > > public C getPrevious(); > > > public C getNext(); > > > } > > > > > > The rule is as follows: > > > > > > rule "WSV 68.1" > > > when > > > // any PreventieveInsluitingsTitel should precede all Straf > > > secondPosition: Straf ( firstPosition: previous ) > > > thirdPosition: > > > PreventieveInsluitingsTitel(previous==secondPosition, fourthPosition:next) > > > then > > > System.out.println( "switching wsv 68.1 "+secondPosition+" > > > "+thirdPosition); > > > thirdPosition.switchWithPrevious(); > > > if(firstPosition!=null){ > > > modify(firstPosition); > > > } > > > modify( secondPosition); > > > modify( thirdPosition); > > > if(fourthPosition!=null){ > > > //in the next statement a classcastexception is thrown > > > modify(fourthPosition); > > > } > > > end > > > > > > results in a classcastexception. The sequence is at that moment { > > > Straf, Straf, PreventieveInsluitingsTitel, Straf } and the middle two items > > > are matched by the LHS secondPosition and thirdPosition. > > > > > > Here's the stacktrace. > > > > > > java.lang.ClassCastException: org.dji.domein.insgro.Straf > > > at > > > org.drools.base.org.dji.domein.insgro.PreventieveInsluitingsTitel$getPrevious.getValue(Unknown > > > Source) > > > at org.drools.base.ClassFieldExtractor.getValue (Unknown Source) > > > at org.drools.rule.Declaration.getValue(Unknown Source) > > > at com.sample.Rule_WSV_68_1_0ConsequenceInvoker.evaluate > > > (Rule_WSV_68_1_0ConsequenceInvoker.java:22) > > > at org.drools.common.DefaultAgenda.fireActivation (Unknown > > > Source) > > > at org.drools.common.DefaultAgenda.fireNextItem(Unknown Source) > > > at org.drools.common.AbstractWorkingMemory.fireAllRules(Unknown > > > Source) > > > at org.drools.common.AbstractWorkingMemory.fireAllRules (Unknown > > > Source) > > > at org.dji.domein.insgro.VolgordeTest.main(VolgordeTest.java:32) > > > org.drools.spi.ConsequenceException: java.lang.ClassCastException: > > > org.dji.domein.insgro.Straf > > > at org.drools.common.DefaultAgenda.fireActivation (Unknown > > > Source) > > > at org.drools.common.DefaultAgenda.fireNextItem(Unknown Source) > > > at org.drools.common.AbstractWorkingMemory.fireAllRules(Unknown > > > Source) > > > at org.drools.common.AbstractWorkingMemory.fireAllRules (Unknown > > > Source) > > > at org.dji.domein.insgro.VolgordeTest.main(VolgordeTest.java:32) > > > Caused by: java.lang.ClassCastException: org.dji.domein.insgro.Straf > > > at > > > org.drools.base.org.dji.domein.insgro.PreventieveInsluitingsTitel$getNext.getValue(Unknown Source) > > > at org.drools.base.ClassFieldExtractor.getValue(Unknown Source) > > > at org.drools.rule.Declaration.getValue(Unknown Source) > > > at com.sample.Rule_WSV_68_1_0ConsequenceInvoker.evaluate(Rule_WSV_68_1_0ConsequenceInvoker.java:22) > > > > > > ... 5 more > > > > > > Thanks in advance for your insight. > > > > > > Regards, > > > > > > -- > > > Joost de Vries > > > > > > > > > _______________________________________________ > > > rules-users mailing list > > > rules-users(a)lists.jboss.org > > > https://lists.jboss.org/mailman/listinfo/rules-users > > > > > > > > > > > > > _______________________________________________ > > rules-users mailing list > > rules-users(a)lists.jboss.org > > https://lists.jboss.org/mailman/listinfo/rules-users > > > > > > > > > -- > Joost de Vries > 06 22375323 > werk: joost.de.vries(a)ordina.nl > privé: joost(a)ziener.org > > -- > Joost de Vries > 06 22375323 > werk: joost.de.vries(a)ordina.nl > privé: joost(a)ziener.org > _______________________________________________ > rules-users mailing list > rules-users(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-users > > > _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users