How are you trying to run the applet? Are you inside a windowed environment like KDE, GNOME, Xfce, ...? Or do you only have a terminal?
Since DISPLAY is not set (which will mostly happen automatically when starting KDE, GNOME etc) my guess is the latter, and that makes it hard to display the applet (or any GUI). Because the JVM cannot find a proper environment to display on it will throw a HeadlessException.
I have added this java -Djava.awt.headless=true to skip the exception. I did this just because the use of that file is pack String arrays , and not sure why it extends Applet ?!?! so anyways Thanks and things working fine..
Does this suppression (-Djava.awt.headless=true ) has any consequences ?