The Object Model Lecture OO02 Classes as Abstract Data Types Understanding Classes and Objects

References Ambler, S., The Object Primer, Cambridge Univ. Press, 2001, Chapter 1 & 2. Booch, G., Object-oriented Analysis and Design, Benjamin Cumings, 1994, Chapter 1. Gamma, E., et al, Design Patterns, Addison Wesley, 1994, Chapter 1

Teaching Points The “Kind-of” Hierarchy What is an object? What is a class? Your first pattern

Review What is an abstract data type? How do multiple architectural views help to cope with complexity? A new kind of hierarchy is a new “kind of@ hierarchy

Decomposition Things or objects in the problem domain It is all in the way we think about the problem

Abstractions Abstract data types Kinds of things Relationships inheritance aggregation use

Hierarchy Akind of@ hierarchy Apart of@ hierarchy

Example: Decomposition of an aircraft as a complex system Remember information-hiding!

The Object Oriented Paradigm No longer a tree of process invocations Now a network of cooperating objects

What is an Object? In-formally A tangible and/or visible thing Something that may be apprehended intellectually Something toward which thought or action is directed

What is an Object? An object has: State (properties, values) Behavior (modifiers, iterators, selectors, constructors, destructors) Identity (???)

What is a class? An abstraction or the Aessence@ of an object represents a set of objects that share a common structure and common behavior (interface) A kind-of-things A single object is simply an instance of a class

Strengths of this kind of decomposition Expression in vocabulary of the problem domain Strong information hiding

What is a Pattern? “A design pattern describes a commonly-recurring structure of communicating components that solve a general design problem in a particular context.” Gamma, et al.

Composite Pattern May be used to describe: File system Graphics objects Aircraft Components etc.

Teaching Points The “Kind-of” Hierarchy What is an object? What is a class? Your first pattern