0.4 Polymorphism - the big picture

Table of contents

• Preface
  • General
  • Viewing tip
    • Figures
    • Listings
  • Supplemental material
• General background information
• Preview
• Discussion and sample code
  • The file named Polymorph02.mxml
  • The file named Driver.as
  • The file named MyShape.as
  • The file named MyCircle.as
  • The file named MyRectangle.as
• Run the program
• Resources
• Complete program listing
• Miscellaneous

Preface

General

This tutorial lesson is part of a continuing series of lessons dedicated to object-oriented programming (OOP) with ActionScript.

The three main characteristics of an object-oriented program

Object-oriented programs exhibit three main characteristics:

• Encapsulation
• Inheritance
• Polymorphism

I explained both encapsulation and inheritance from a big-picture viewpoint in previous lessons. (See Baldwin's ActionScript programming website .) There are two different ways to implement polymorphism:

• Polymorphism based on class inheritance
• Polymorphism based on interface inheritance

I will explain and illustrate polymorphism based on class inheritance in this lesson and will explain and illustrate polymorphism based on interfaceinheritance in the next lesson.

Several ways to create and launch ActionScript programs

There are several ways to create and launch programs written in the ActionScript programming language. Most of the lessons in this series willuse Adobe Flex as the launch pad for the sample ActionScript programs.

An earlier lesson titled The Default Application Container provided information on how to get started programming with Adobe's Flex Builder 3. (See Baldwin's Flex programming website .) You should study that lesson before embarking on the lessons in this series.

Some understanding of Flex MXML will be required

I also recommend that you study all of the lessons on Baldwin's Flex programming website in parallel with your study of these ActionScript lessons. Eventually youwill probably need to understand both ActionScript and Flex and the relationships that exist between them in order to become a successfulActionScript programmer.

Will emphasize ActionScript code

It is often possible to use either ActionScript code or Flex MXML code to achieve the same result. Insofar as this series of lessons is concerned,the emphasis will be on ActionScript code even in those cases where Flex MXML code may be a suitable alternative.

Viewing tip

I recommend that you open another copy of this document in a separate browser window and use the following links to easily find and view the figures andlistings while you are reading about them.

Figures

• Figure 1 . File structure for Polymorph02.
• Figure 2 . Program output at startup.
• Figure 3 . Sample output from area method of a MyShape object.
• Figure 4 . Sample output from area method of a MyCircle object.
• Figure 5 . Sample output from area method of a MyRectangle object.