Interfaces and Greenfoot My colleague and I are considering bringing Greenfoot into our AP classes this year, and while Interfaces have been removed from the AP subset, we will continue to teach them.

Greenfoot itself seems to either not have, or to have thoroughly hidden, interfaces.  However, we are not interested in reinventing the wheel if it's not necessary.  Are there good lab activities that heavily feature interfaces already developed for Greenfoot?

Alternatively, are there any strong lab ideas for Greenfoot and interfaces that we could run with?
Yes, Greenfoot certainly has interfaces. I doubt that they would take them out. The people who built greenfoot are likely as appalled as I am about the College Board action on interfaces. But there is no UI element that specifically adds a new interface to a project. 

But they may not appear in the same place that most classes do in the sidebar. Look at the bottom of the list. 

Use the menu option to create a "New Class". Edit the resulting template to change it to a legal interface. Compile and save. This was with v 3.5. 

You can do the same with other "class-like" things such as enumerations. The compiler hiding behind greenfoot is all of Java. 

You can also go to https://greenroom.greenfoot.org and ask such questions there (after joining). 

Also, many of the labs that you find on both the greenfoot and greenroom sites will use interfaces.