We present in this paper the application of constraint solving techniques to the validation and automated test cases generation for Java programs, annotated with JML specifications. The Java/JML code is translated into a constraint representation based on a subset of the set-theory, which is well-suited for modelling object-oriented programs. Symbolic code execution techniques can then be applied to produce test cases, using classical structural test selection criteria, or to detect possible runtime errors, and non-conformances between the Java code and its embedded JML model.