Swing Pluggable Look and Feel
Java Swing provide pluggable look and feel features.
Found free / opensource look and feel (like theme engine in GTK+) in these site:
Just copy the lookAndFeel jar in to $JAVA_HOME/jre/lib/ext/ and edit $JAVA_HOME/lib/swing.properties with the following line:
swing.defaultlaf=com.jgoodies.looks.plastic.PlasticLookAndFeel
The RHS should be the class name of the look and feel class.