Concrete classes 3.6. Parameterization Sather programs are textually made up of classes . Classes are used to define the code and storage that make up types . Each object is an instance of a type. Types can be thought of as representing sets of objects at runtime.
Objects never change their type.
There are also abstract types, which represent sets of concrete types. Immutable, reference, external, and abstract types are defined textually by immutable , reference , external , and abstract classes. Partial classes define code that does not have corresponding objects or types, and may be included by other classes to obtain implementation. The type graph for a program is a directed acyclic graph that is constructed from the program's source text. Its nodes are types and its edges represent the subtype relationship.