If you just want to translate it into your local language. Please check out [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=100.0]Translate Strings into local language format[/url] for all the simulations under category : [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php#2]JDK1.0.2 simulations (1996-2001) [/url].

If you really need the source code, just download the attachment file gas2d.java.
However, it was written with JDK1.0.2 more than 10 years ago!