In this example, we would like to make the individual lights on the traffic light "clickable" so that clicking the mouse on a light will turn it on (and turn off the light that is currently on). How do we need to change the previous program to do this?

Here is a solution in the form of the class ChangeableTL. A driver that demonstrates how it works.

This is the output after a few clicks.

However, it is also instructive to see the diagnostic output that is written to System.out.