You just need to communicate the right information to the right places.  
The right way to do this depends very much on the abstraction involved.  
There are several possibilities, and these are the ones that come to
mind immediately.

1. If these panes are really so connected, then perhaps you should build
them all in the same place, instead of writing a separate class for
each.

2. You could have each pane share the text field models (Document
instances) for each of the text fields.  The panes with text fields
would store those Document instances in the shared location as the
fields are created, and the final pane would read from those Document
instances.  A variation is to store JTextField instances instead of
models.

3. You could have each pane of the JTabbedPane register a ChangeListener
on the JTabbedPane itself, and when it loses selection have it be
responsible for filling in some kind of higher-level model object with
the data from the pane.

Hello Gil,

if you need the text of all textfields and the order of the textfields
does not matter then you might just walk through the component tree:
- Get all children of any pane with getComponents(),
- make a for loop and look for children of type JTextField,
- also search for textfields in child-panes, that's it.
You can do the job recursive.

If the order of the textfields matters or those textfields do have any
other necessary property you need when processing the text then you
might design a panel---say MyExtraPanel---containing just one
textfield. MyExtraPanel could have an attribute 'xyz' and a getter for
that. You could get all MyExtraPanels the same way you get all
JTextFields and call getXyz().

Greeting
   Dirk