java.lang.IncompatibleClassChangeError error while using HashSets ----------------------------------------------------------------- Key: DROOLS-900 URL: https://issues.jboss.org/browse/DROOLS-900 Project: Drools Issue Type: Bug Components: core engine Affects Versions: 5.6.0.Final Reporter: Pravasis Pattnaik Assignee: Mario Fusco Priority: Minor Attachments: compiled-drl.txt, req.txt In the compiled drl file we were using (Sets.newHashSet(e1,e2,..)).contains(x) then we get an exception java.lang.IncompatibleClassChangeError: Class XYZ does not implement the requested interface java.util.Collection on large input sets.Here XYZ is our input ruleRequest to be evaluated. If I change it to Sets.newHashSet(e1,e2,..).contains(x) it fixes everything.