It is clear that the properties that are made visible are a subset of the properties abstracted inside the abstraction barrier. Analysis, design and implementation concepts 3.1. A class describes a set of entities, which can be either or abstract. The set of entities in a class share the same conceptual basis. An object is an instance of a class.
Classes serve as templates for the creation of objects.
Most object-oriented languages support a type of classes called abstract classes. An abstract is a class C, with at least one operation left unimplemeted. Objects communicate through message passing. This occurs when an object receives a message. A message is an action asking objects to behave in some way.