Defining classes

Classes encapsulate state and behavior. Defining a class requires a mechanism to define the set of data members and properties that represent the class's state and a set of related methods and events that provide the behavior of the class. The members of a class comprise the type of the object defined by the class. As with other data types, the compiler verifies that references to a class and its members are consistent with its type. Another object type is an interface, which also has members, and provides a means to enforce a consistent definition for the corresponding members of similar class types. (For more information on defining interface types, see Defininginterfaces.) Class-based objects are running instances of classes. At run time there can be many instances of a class, each with its own state. There can also be object references of different types pointing to a single class instance that represents all these types. A valid reference type can be a class in its class hierarchy or an interface that it implements. For more information on how an object can represent more than one type, see Designing Objects: Inheritance, Polymorphism, and Delegation.

After beginning a class definition with a CLASS statement, which specifies the class type and its relationship to any other class and interface types, you can define a user-defined class with the following types of elements:

Together with the CLASS statement, all of these elements provide the mechanisms for defining classes as described in the following sections: