How to Build a String in DRL file - drools

Question

String i;
String j;
String k;
i.concat(j).concat(k);
Now I want to write this in DRL file.
rule "X"
when
xx : X(i.concat(j).concat(k))
I am new with Drools, please help me to build the string inside the when condition in DRL file.

Answer 1

I can't think of any good reason to want to do this. The "when" clause is for checking conditions (broadly equivalent to an "if" statement.)
Now, assuming you have some input object X that looks like this:
class X {
String i;
String j;
String k;
}
... you can create a String that's the concatenated form of the i, j and k values in a few ways.
One way would be like this:
rule "Str from x - v1"
when
X( $i: i, $j: j, $k: k )
$str: String() from $i.concat($j).concat($k)
then
// do something with $str
end
If you're just trying to compare to the concatenated value, you could just, you know, concatenate the fields at the time of comparison instead of assigning them to a variable:
rule "Just compare it"
when
X( $i: i, $j: j, $k: k )
SomethingElse( myStr == $i + $j + $k )
then
// ...
end
Since $i, $j, and $k values are immutable (since they're Strings), you can concatenate them at any time and always get the same result, so it's not even a case of "the values might change from under me". So while there's very little reason to ever do this, here's how you'd go about it.