Object-oriented Programming has been effective in reducing code complexity in sequential programs, but in current practice, concurrent programs still present a number of challenges. We present here a model of object-oriented programming that identifies concurrent tasks and the relationship between objects and tasks , effectively making objects concurrency-aware . This awareness is formalized in a parallel programming model where every object plays a role in every task (e.g., the readonly role). When an object is shared with a new task, it adapts to the new sharing pattern by changing its roles, and therefore its behavior, i.e., the operations that can be performed with this object. This mechanism can be leveraged to prevent interfering accesses from concurrently executing tasks, and therefore makes parallel execution deterministic. To this end, we present a role-based programming language that includes several novel concepts (role transitions, guarding, slicing) to enable practical, object-oriented deterministic parallel programming. We show that this language can be used to safely implement programs with a range of different parallel patterns. The implementations to 8 widely used programming problems achieve substantial parallel speedups and demonstrate that this approach delivers performance roughly on par with manually synchronized implementations.