EJS Source code are available for all the simulations created with EJS, i.e.
Simulations under category [ [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=collapse;c=3;sa=expand#3]Easy Java Simulations (2001- ) [/url] ]

For applets created with JDK1.0.2 (I created those between 1996-2001), source code are only included with very few download ZIP files.  I did  not add source code in the ZIP files, because most of the user did not need it. And those (including pendulum applet shown in this topic) are all created with JDK1.0.2
However, I just sent the source code to your email. You might need to change some of the code if you want to compile those code with current version JDK.