Are you teaching Advanced Placement Computer Science? Are you looking for supplemental exercises that may help you students with the concepts? If so this announcement may be of interest to you. Pex for Fun has been around for a while offering coding duels in C#, F# and Visual Basic. Recently though it was decided to invest some time, money and effort to adapt some exercises specifically to help learn APCS concepts. Most students find the differences between Java and C# pretty minor at this level so most APCS students will find this doable even if they have only been taught Java previously.
Pex4fun APCS (http://pexforfun.com/apcs) is an online lab for APCS. It features 156 coding duels organized in chapters mapping the APCS program. In each coding duel, the student has to implement a program against a specification. At each attempt, pex4fun analyzes the student program together with the specification program to produce an input/output table showcasing cases where the behavior matches or not. Based on this feedback, the student can iteratively refine his solution until his program has the same observable behavior as the specification program.
Pex4fun is free, runs in any browser and provides a rich auto-completion experience.