Hi Erwin,
You should include the module name as well eg Core.instantiate(context, "System.UserRole")
Kind regards,
Jeroen
Edit: To give a more complete answer: use __Select3.setValue() to modify this object.
Also note that using plain text strings will work but is not recommended. You can better import the Proxy for the entity:
Under imports add a line:
import YourModuleName.proxies.Select3;
And use: Core.instantiate(context, Select3.entityName)
This way when your entity name changes you do not have to change your Java code.
Why use JAVA in the first place?