There has to be something I do not understand about using rules.

Take this simple class and rules and I don’t understand the output.

First, when the rule constructor is executed it appears as though only the value 1 was put into the map, then it runs rule test1 and then it sees only values 2 and 3.

Secondly, look at rule test2 right now the RHS displays true, BUT if you comment out the eval(true) and uncomment either of the evals you get a nullpointer at runtime. I do not understand why there is a null pointer. Any insight would be wonderful, I have been banging my head against this for a bit and it’s probably something stupid.

Thanks!

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package test.map;

import java.util.HashMap;

import java.util.Map;

public class Test

{

            public Test()

            {

                        values = new HashMap<String, Object>();

            }

            private Map<String, Object> values;

            public Map<String, Object> getValues()

            {

                        return values;

            }

            public void setValues(Map<String, Object> values)

            {

                        this.values = values;

            }

}

-----------------------------------------

package test.map

import java.math.BigDecimal;

import java.util.Map;

rule "Constructor"

   no-loop true

   when

              eval(true);

      $t : Test(values:values)

   then

      drools.setFocus("test2");

      drools.setFocus("test1");     

      values.put("one", new BigDecimal("1"));

      addValue($t, "two", new BigDecimal("2"));

      $t.getValues().put("three", new BigDecimal("3"));

      update($t);

      System.out.println("in constructor");

      System.out.println(values);

      System.out.println();

end

rule "test1"

   no-loop true

   agenda-group "test1"

   when

      eval(true);

      $t : Test(values:values)

   then

              System.out.println("in test1");

      System.out.println(values);

      System.out.println();

end

rule "test2"

   no-loop true

   agenda-group "test2"

   when

      eval(true);

      $t : Test(values:values)

      //eval(((BigDecimal)values.get("two")).equals(new BigDecimal("2")));

      //eval(((BigDecimal)$t.getValues().get("two")).equals(new BigDecimal("2")));

   then

      System.out.println(((BigDecimal)$t.getValues().get("two")).equals(new BigDecimal("2")));

end

function void addValue(Test t, String key, BigDecimal value)

{

   t.getValues().put(key, value);

}

---------------------------------------

This is a simple class to start it up.

---------------------------------------

package test.map;

import java.io.InputStreamReader;

import java.io.Reader;

import org.drools.RuleBase;

import org.drools.RuleBaseFactory;

import org.drools.WorkingMemory;

import org.drools.compiler.PackageBuilder;

import org.drools.rule.Package;

public class Mainclass

{

            public static void main(String[] args)

            {

                         try

                         {

                                     //load up the rulebase

                                     RuleBase ruleBase = readRule();

                                     WorkingMemory workingMemory = ruleBase.newStatefulSession();

                             Test test = new Test();

                             workingMemory.insert(test);

                             workingMemory.fireAllRules();

                         }

                         catch (Throwable t)

                         {

                            t.printStackTrace();

                         }

            }

            /**

     * Please note that this is the "low level" rule assembly API.

     */

            private static RuleBase readRule() throws Exception

            {

                        Reader source = new InputStreamReader(Mainclass.class.getResourceAsStream("/Nulltest.drl"));

                        System.setProperty("drools.compiler", "JANINO");

                        PackageBuilder builder = new PackageBuilder();

                        builder.addPackageFromDrl( source );

                        Package pkg = builder.getPackage();

                        RuleBase ruleBase = RuleBaseFactory.newRuleBase();

                        ruleBase.addPackage( pkg );

                        return ruleBase;

            }

}

Jeff Shutt

Software Developer

SOS Staffing Services

(801) 924-0429

shuttj@sosstaffing.com