Adobe Max 2007 – Chicago
Peter Elst – OOP for AS3

Myth – Do you need to use OOP if you are a lone programmer?  YES

Concepts of OOP

• Classes
• Inheritence
• Encapsulation
• Polymorphism
• Interfaces

Introducing Design Patterns

What is OOP?

OOP structures code into reusable units that provide a blueprint for any number of instances that are created from it.

In OOP there are

Class = Blueprint
Object = House

 What’s new in AS3?

• Display List API
• DOM3 Event Model
• ECMScript for XML(E4X) – easy way to query XML
• Runtime Error Checking – Prevents you from making major mistakes
• Regular Expressions –
• Method Closures
• Protected Scope
• etc…

Classes

• Classes describe an object using properties and methods
• Anynumber of instnace can be created from

Inheritance

•  Allows you to extend classes, propeties of a super class(i.e. the clas which to extend
• AS3 classes require the override keyword to override methods or por
• The final keywords disallows for any extending of classes

Inheritance vs. Composiion

• Composition does not extend a class but instantiates it at runtime.
• Inheritance is used for an ‘is a’ relationship, whereas composition typically implies a ‘has a’ relationship
• Composition gives control over creation and destruction and garbage collections

Encapsulation

• Allows you to protect the inner workings of a class through the use of access modifiers
• Provide an API to interact with your class through getter/setter methods
• Keywords
  • public – accessible everywhere
  • private -only accessible within class
  • protected -within class and derivative classes
  • internal – accessible within same package

Polymorphism – (the easiest concept in OOP)

• Allows different classes to respond to same method names with their own implementation.
• Common mehtod names make classes interchangeable at runtime.
• Uses override to change the function at runtime

Interfaces

• Allows you to specify a set f methods that classes are required to implement
• Classes can implement multiple interfaces, interfaces can extend each other
• Interfaces can be seen as contracts to be developed against.
• Interfaces just implements a list of code

    public interface Cat implements (IAnimal, ICuteness)

Patterns

Observer Pattern

• Don’t make any references to the classes that you listening to.

Singleton

• Eables a class to have just one instanceaccessible through a static method
• Singleton classes provide a global point of access
• AS3 doesn’t yet allow constructors to be private so you must do an if statement to check if it has already been called.