Running drools with OpenJDK9 (10 May 2016) gives "type java.lang.Object cannot be resolved" and "java.io.Serializable cannot be resolved" due to ECJ 2.5 -------------------------------------------------------------------------------------------------------------------------------------------------------- Key: DROOLS-1169 URL: https://issues.jboss.org/browse/DROOLS-1169 Project: Drools Issue Type: Bug Components: core engine Reporter: Geoffrey De Smet Assignee: Mario Fusco Labels: java9 The code below runs perfectly with OpenJDK 8 (and even 6 and 7). To reproduce, use JDK 9 ( https://jdk9.java.net/download/ ) and in optaplanner-core, run XStreamXmlSolverFactoryTest [1] (or mostly any other test that builds a DRL file) to get this error: {code} 15:56:40.229 [main] ERROR o.d.c.k.b.impl.AbstractKieModule - Unable to build KieBaseModel:defaultKieBase Rule Compilation error : [Rule name='Conflict'] org/optaplanner/core/api/solver/Rule_Conflict903142795.java (1:0) : The type java.lang.Object cannot be resolved. It is indirectly referenced from required .class files org/optaplanner/core/api/solver/Rule_Conflict903142795.java (1:0) : The type java.io.Serializable cannot be resolved. It is indirectly referenced from required .class files org/optaplanner/core/api/solver/Rule_Conflict903142795.java (3:337) : Implicit super constructor Object() is undefined for default constructor. Must define an explicit constructor org/optaplanner/core/api/solver/Rule_Conflict903142795.java (6:569) : java.lang.Exception cannot be resolved to a type java.lang.IllegalStateException: There are errors in a score DRL: Error Messages: Message [id=1, level=ERROR, path=org/optaplanner/core/api/solver/testdataScoreRules.drl, line=31, column=0 text=Rule Compilation error The type java.lang.Object cannot be resolved. It is indirectly referenced from required .class files The type java.io.Serializable cannot be resolved. It is indirectly referenced from required .class files Implicit super constructor Object() is undefined for default constructor. Must define an explicit constructor java.lang.Exception cannot be resolved to a type] {code} That tests builds this DRL: {code} package org.optaplanner.core.api.solver; dialect "java" import org.optaplanner.core.api.score.buildin.simple.SimpleScoreHolder; import org.optaplanner.core.impl.testdata.domain.TestdataValue; import org.optaplanner.core.impl.testdata.domain.TestdataEntity; global SimpleScoreHolder scoreHolder; // ############################################################################ // Constraints // ############################################################################ rule "Conflict" when TestdataEntity(value != null, $leftValue : value) TestdataEntity(value == $leftValue) then scoreHolder.addConstraintMatch(kcontext, -1); end {code} Not sure where the Object constructor reference comes from... This might be a JDK 9 upstream issue. Note: don't build drools with OpenJDK9 as that will fail sooner :) [1] https://github.com/droolsjbpm/optaplanner/blob/master/optaplanner-core/sr...