This is the first java applet that I have created when I learned java almost 12 years ago (with JDK 1.0.2).

I used a text editor to wrote the code, line by line. Draw arrow, draw line ... etc.
And I have created near 100 java applets by the same way.
But I switch to EJS when listened to the talk by its author (Paco, he and I were invited to give a talk at AAPT meeting at the same session).
Please check the following similar applets which were all created with EJS. (and you can download EJS source and load it inot EJS and watch how I did it. You can modified it to generate new simulation,too.)

1. [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=377.0]object in front of concave/convex lens  [/url]
2. [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=376.0]object in front of concave/convex mirror[/url]
3. [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=121.0]Lens (thick lens) and Mirror[/url]

It is much easier to create new simulation with EJS. This tool focus on the physics instead of java programming.