Featherweight Wrap Java

We present an extension for a Java like language with a mechanism for dynamically extending object behaviors. Our approach consists in moving the addition of new features from class (static) level to object (dynamic) level: the basic features of entities (representing their structure) are separated from the additional ones (wrapper classes whose instances represent run-time added behaviors). At run-time, these entities can be dynamically composed by instantiating wrapper objects which are attached to basic entities. We formalize our extension by adding the new constructs to Featherweight Java; the core language so extended (Featherweight Wrap Java) is type safe.