Indeed, I don't think Swing has changed much since 1.3 (haven't used 1.2, so
don't know about that).

From the 1.4 changelog:

Java Foundation Classes (JFC)
Several new enhancements have been made to the Java Foundation
Classes/Swing APIs in J2SE 1.4:

New JFC/Swing features include support for spinners, scrollable tabbed
panes, and indeterminate progress bar controls.
Swing component data can now be transferred between applications using cut,
copy, and paste functions in addition to full drag-and-drop support across
all Swing components.
A new API for the long-term persistence of JavaBeans technology will allow
developers to create UI designs that are portable between IDEs.
To help applications adapt to different users and environments, a new
Preferences API provides a way to store, retrieve, and modify data from
applications.
The new full-screen exclusive mode API supports high performance graphics by
suspending the windowing system so that drawing can be done directly to the
screen; a benefit to applications such as games.
A redesigned focus architecture addresses many focus-related bugs caused by
platform inconsistencies and incompatibilities between AWT and Swing
components.
Undecorated frames allow a Java application to turn off the creation of
frame decorations such as native title bars, system menus, borders, or
other native operating system dependent screen components.
Other JFC improvements include an updated file chooser for Windows, a new
Auditory Feedback mechanism, higher quality font rendering, mouse wheel
support, Section 508 accessibility compliance, support for Macintosh style
menu bars, and a comprehensive new Print Service API.