[rules-users] Problem with "!=" field constraint
Hi,
I have a problem with a rule which uses a "!=" field
constraint. The following code illustrates the
problem.
import org.drools.*;
import org.drools.compiler.*;
import org.drools.rule.Package;
import java.io.*;
public class DroolsTest {
private RuleBase rules;
private StatefulSession memory;
public DroolsTest(File file) throws Exception {
rules =RuleBaseFactory.newRuleBase();
memory=rules.newStatefulSession();
rules.addPackage(loadPackage(file));
}
protected Package loadPackage(File file) throws
IOException {
FileInputStream stream=null;
try {
stream=new FileInputStream(file);
return(loadPackage(stream));
}
finally {
if (stream!=null)
stream.close();
}
}
protected Package loadPackage(InputStream stream)
throws IOException {
try {
PackageBuilder builder=new PackageBuilder();
builder.addPackageFromDrl(new
InputStreamReader(stream));
return(builder.getPackage());
}
catch(Exception ex) {
throw new IOException();
}
}
public StatefulSession getSession() {
return(memory);
}
public static void main(String ... args) {
try {
DroolsTest test=new DroolsTest(new
File(args[0]));
SpecialString first42 =new SpecialString("42");
SpecialString second42=new SpecialString("42");
test.getSession().insert(new
SpecialString("World"));
test.getSession().insert(first42);
test.getSession().insert(second42);
System.out.println("Fact handle:
"+test.getSession().getFactHandle(first42));
System.out.println("Fact handle:
"+test.getSession().getFactHandle(second42));
System.out.println("Firing rules ...");
test.getSession().fireAllRules();
}
catch (Exception ex) {
ex.printStackTrace();
}
}
}
I'm inserting three different objects in the working
memory of the Drools 4 Engine. Two of the three
objects have the same text - "42". When I'm using the
following rule
package test
rule "A test"
when
x : SpecialString()
y : SpecialString(this!=x)
then
System.out.println(x+"/"+y);
end
I get the output
Fact handle: [fid:2:2:42[SpecialString@fde8da]]
Fact handle: [fid:3:3:42[SpecialString@e4d6ef]]
Firing rules ...
42[SpecialString@e4d6ef]/World[SpecialString@faa824]
World[SpecialString@faa824]/42[SpecialString@e4d6ef]
42[SpecialString@fde8da]/World[SpecialString@faa824]
World[SpecialString@faa824]/42[SpecialString@fde8da]
which is not what I expect. Why are combinations of x
and y with the two "42"-instances not listed, i.e.
Why doesn't the output contain
42[SpecialString@e4d6ef]/42[SpecialString@fde8da]
42[SpecialString@fde8da]/42[SpecialString@e4d6ef]
The class SpecialString uses the standard equals(...)
and hashCode(...) implementation, so these should be
based on the object references, not the content:
public class SpecialString {
private String text;
public SpecialString(String text) {
this.text=text;
}
public String getText() {
return(text);
}
@Override public String toString() {
return(getText()+"["+super.toString()+"]");
}
}
Best regards
Markus
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