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.

Leaf

Component

Composite

1

0..*children

0..*

1

Client <<uses>>

Teaching Points

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