Copy selected value from select box to a read only text field.

Hi!

I just set up joget workflow on my computer and I need to copy the selection from select box to a read only textfield. I'm new to beanshell. How can I do this?

thanks in advance

EDIT1.:So if I am right this code stores the value from the selectbox in the variable "sbvalue":

import java.util.Collection;
import org.joget.workflow.model.*;
import org.joget.workflow.model.service.*;

WorkflowManager wm = (WorkflowManager) pluginManager.getBean("workflowManager");
String sbvalue ="#formName.fieldName#";     

I suppose i only need to add the value of "firstname" to the read only text field but i did not find anything that helped me.  Also I dont know where toput this code in the form.