I do not know why, it works fine when I re-compile your code and upload it again.
Please check out the following uploaded applet.

/htdocs/ntnujava/ejsuser/2/users/lookang/Car5_pkg/Car5.propertiesFull screen applet or Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop. This work is licensed under a Creative Commons Attribution 2.5 Taiwan License
Download EJS jar file(1214kB):double click downloaded file to run it. (3 times by 1 users) , Download EJS source (1 times by 1 users) View EJS source

from lookang
eye this applet because it is missing the png, will re web at the top post!