You have to use Core.change (http://apidocs.mendix.com/runtime/classcom11mendix11core11_core.html#a883040302bab2117b8b64f3765e0ae5f) to update the object in the cache too. If you don't use that then you'd have to commit first or return the object from your java action and show that.
Then refresh like Herbert says.
Hi Simon, Most likely you have to let the framework now that the object has to be refreshed in the client (the Java way of the refresh in client check box). You can do that within an action with:
An easier way for changing members is to use the proxy's, generated by the framework. If your object is a Person for example you can do something like this: Person person = Person.initialize(object); After that you can use the person.set and person.get functions.