Jess bind this instance of java object - jess

Question

I want to do something like that in Jess:
(bind ?instance (this))
The only way I get it working is by using "new Object" instead of "this".
How can I get it working?

Answer 1

Actually there's three ways you can access a Pojo from the Jess environment, and a fourth if it is a singleton.
public class Main {
public static Main theInstance;
public static Main getInstance(){ return theInstance; }
private String user = "Joe";
public String getUser(){ return user; }
public static void main( String[] args ) throws Exception {
Main main = new Main();
Main.theInstance = main;
Rete rete = new Rete();
// as a global
Defglobal glob = new Defglobal( "*main*", new Value( main ) );
glob.reset( rete );
// as a store member
rete.store( "main", main );
// as a fact
rete.add( main );
// execute demo clp
rete.batch( "two.clp" );
}
}
And the .clp is:
(printout t "?*main* = " ?*main* crlf)
(printout t "?*main*.user = " (?*main* getUser) crlf)
(printout t "main = " (fetch main) crlf)
(printout t "main.user = " ((fetch main) getUser) crlf)
(defrule get-main-user
(Main (user ?user))
=>
(printout t "a Main(slot user) = " ?user crlf)
)
(run)
(printout t "Main.theInstance = " ((call Main getInstance) getUser) crlf)
Output:
?*main* = <Java-Object:Main>
?*main*.user = Joe
main = <Java-Object:Main>
main.user = Joe
a Main(slot user) = Joe
Main.theInstance = Joe

Answer 2

Presumably you are passing some Jess code to the Rete.exec() method, and want a reference to the object that's making the call. You just have to inject it into Jess yourself. Either use Rete.store() to store the object in Jess, then use (fetch) to retrieve it from storage in the Jess code, or use the methods of the global context object -- see Rete.getGlobalContext() -- to set a variable to refer to the Java object, then use the variable in the Jess code.