The main objective of a 'Design by Contracts' approach as applied to object-oriented systems, is to develop complete and consistent method contracts for the objects of the system. In this work, we propose a practical approach to develop these contracts for an object from its annotated structural representation, namely, UML constrained class diagram. We generate, simulate, and refine an object statechart from an initial set of method contracts which in turn help further validating and enhancing these contracts. The impact of this analysis can be multifold: first, it identi- fies various discrepancies like incomplete and inconsistent class specifications, second, a correct and consistent object statechart model is obtained from which reliable automated code and unit tests can easily be generated, third, facilitate essential and effective verification for software re-use, forth, the resulting statechart and class specifications are in a lock-steps which facilitates effective incremental development and change management and fifth, it allows a modeler to specify object's dynamic requirements declaratively on an abstract level, without the need to use full operational dynamic diagrams. We have also designed a tool ObjectSim that performs automated statechart generation and their interactive simulations. We demonstrate our approach using an example and discuss other related issues.