Why not provide a full-fledged design-by-contract facility with preconditions, postconditions and class invariants, like the one in the Eiffel programming language?
We considered providing such a facility, but were unable to convince ourselves that it is possible to graft it onto the Java programming language without massive changes to the Java platform libraries, and massive inconsistencies between old and new libraries. Further, we were not convinced that such a facility would preserve the simplicity that is the hallmark of the Java programming language. On balance, we came to the conclusion that a simple boolean assertion facility was a fairly straight-forward solution and far less risky. It’s worth noting that adding a boolean assertion facility to the language doesn’t preclude adding a full-fledged design-by-contract facility at some time in the future. The simple assertion facility does enable a limited form of design-by-contract style programming.
