Chapter 2: Introduction to Object Orientation Object-Oriented Systems Analysis and Design Joey F....
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Transcript of Chapter 2: Introduction to Object Orientation Object-Oriented Systems Analysis and Design Joey F....
Chapter 2:Chapter 2:Introduction to Object OrientationIntroduction to Object Orientation
Object-Oriented Systems Analysis and Design
Joey F. George, Dinesh Batra, Joseph S. Valacich, Jeffrey A. Hoffer
Chapter ObjectivesChapter Objectives After studying this chapter you should be
able to:– Define an object.– Understand the terms class, attribute, and
operations.– Explain generalization, polymorphism, and
inheritance.– Define association.– Describe modeling and the Unified Modeling
Language.
What is an Object?What is an Object?
An entity that encapsulates data/attributes and behavior/operations
- Objects are categorized into classes
- Each individual object is an instance of a class
What is a Class?What is a Class?
• A category of objects that share the same data attributes, and operational behavior
• All objects are instances of classes
• Classes are like templates, or blueprints, or types for objects
What is Encapsulation?What is Encapsulation?
The characteristic of object-orientation in which data and behavior are bundled into a class and hidden from the outside world
Access to the data and behavior is provided and controlled through an object’s interface,aka. API (application programming interface)
Name
Attributes
Operations
What is an Attribute?What is an Attribute?
• Attribute – is a named property of a class that describes the various characteristics that objects within the class will have
• Attributes are the way classes encapsulate data
• Attributes are mostly nouns
Attributes are properties containing values
Minus sign indicates these are private (hidden)
What is an Operation?What is an Operation? A behavior for an object
Implemented in OO classes as methods
A method is where the program code resides
Methods are identified and invoked by their signatures, including their names and parameters
Methods are mostly verbs
A method signature identifies the interface to the method
A method implements the behavior
Method signatures
Plus sign indicates these are public (accessible)
What is Generalization?What is Generalization?A relationship between
a parent class (more general) classand a child class (more specific)
The more specific the class is, the more additional attributes and operations it has
A parent class Vehicle is more generalA child class Car is more specific
What is Inheritance?What is Inheritance?
The mechanism by which the more specific (child) class in a generalization relationship includes the attributes and operations of the more general (parent) class
A generalization relationship is represented by an arrow from the subclass to the superclassSubclasses
inherit all attributes and operations of superclasses
What is a Message?What is a Message?
A message is the way one method or process invokes (calls) another method or process
The message will include the name of the method, and the value of parameters the method expects in parenthesis
Example: add_order(123456)
What is Polymorphism?What is Polymorphism? The ability for different subclasses to respond to
identical messages in different ways
Polymorphism = “having many forms”
Different behaviors for the same message
Each subclass (e.g. FullTimeEmp, PartTimeEmp) will implement the same method (e.g. calcSalary) differently
Here, each type of vehicle has its own version of calcPrice( )
What is a Component?What is a Component?
A replaceable part of a system providing a clearly defined function through a set of interfaces
Group of classes working together toward a common end; a subsystem
What is an Interface?What is an Interface?
The mechanism by which users of a component invoke its behaviors and manipulate its properties
The interface is implemented by method signatures
What is a Package?What is a Package?
A general-purpose mechanism for organizing elements into groups
Group of classes sharing similar characteristics or purposes
A Package is akin to a folder on your operating system
The Sales package might include: a product, inventory and customer classes
What is an Association?What is an Association?
A relationship or a link between two or more classes
Three types:– Simple associations: no ownership (e.g. people, places) – Aggregations: whole-part relationships where the part
can exist independently of the whole (e.g. team, player)– Compositions: whole-part relationships where the part
is fully dependent on whole, and cannot exist without it(e.g. sales_order and sales_order_line items)
What is Association Multiplicity?What is Association Multiplicity?
Identifies the number of associated entities that can exist for an entity
Three types:– One to One: one entity is associated with a single entity – One to Many: one entity is associated with zero or
more entities– Many to Many: one entity “A” is associated with zero
or more entities “B” , and one entity “B” is associated with zero or more entities “A”
This is a association, showing roles and multiplicities
Unified Modeling Language Unified Modeling Language (UML)(UML)
A standard notation for representing object-oriented systems created by Grady Booch, James Rumbaugh, and Ivar Jacobson
Boxes represent classes, components, packages, objects– Containing attributes and operations– Provide interfaces to external entities
Lines represent relationships, (either generalization and association)
Sample UML
Diagram
UML DiagramsUML Diagrams Class Diagram – shows classes and relationships. Use Case Diagram – describes sequences of action involving
actors. Sequence Diagram – shows interaction with objects in a
time-ordered manner. Collaboration Diagram – interaction with objects without time
relevance. Activity Diagram – shows data flow from one activity to
another. Similar to flow chart diagrams Statechart Diagram – shows transition of an object from one
state to another as a response to an event Package Diagram – shows components in packages.
RecapRecap After studying this chapter we learned to:
– Define an object.– Understand the terms class, attribute, and
operations.– Explain generalization, polymorphism, and
inheritance.– Define association.– Describe modeling and the Unified Modeling
Language.