Very cool stuff. I wonder if there is any way to integrate something like KeYmeara (http://symbolaris.com/info/KeYmaera.html) for a way to prove correctness of Java systems (or components of Java systems).
While I'm not sure if we may count those as "programmation by contract", some Java tools provide (some) static analysis:
- Findbugs
- IntelliJ IDEA does some nullness analysis : http://www.jetbrains.com/idea/documentation/howto.html
- JSR 305 (Annotations for Software Defect Detection in Java) attempted to standardize on a set of annotations. We use it in our project, mainly the @Nonnull at the moment... I believe Findbugs considers these annotations.
- CodePro Analytix, also recently open sourced by Google, might also do some static analysis: http://code.google.com/javadevtools/codepro/doc/index.html
- Eclipse might too (any expert Eclipse user knows?)
I think there is still a lot to do in this space. "Contracts for Java" is a step in the right direction :)