There have been some good answers, but I would like to cover a slightly different aspect. Things that Swing provides beyond AWT.
Components
Swing supports styled documents in JEditorPane
& JTextPane
& to a limited extent using HTML in some other JComponents
. AWT does not support styled documents in any component.
AWT provides no tree based structure like JTree
, no tabular structure such as JTable
, no version of JToolBar
.
AWT has no equivalent (that I can find or recall) for JColorChooser
& none for the simple utility class - JOptionPane
.
Listeners
As mentioned in a comment, see the 20+ extra/alternate listeners in the javax.swing.event
package.
Pluggable Look & Feel
Swing components can be set to a particular look & feel at run-time, including a native PLAF.
See the screen shots on the Nested Layout Example for some more samples.
Layouts
In addition to the plethora of AWT layouts, Swing provides:
BoxLayout
GroupLayout
OverlayLayout
ScrollPaneLayout
SpringLayout
ViewportLayout
Other
There is probably a lot more I missed in that brief description, but the bottom line is that Swing is an altogether newer and more enabled GUI toolkit.
Swing both builds on, and relies heavily on, classes in the AWT.
javax.swing.event
package. ;) – Poole