Fall 2008ACS-1805 Ron McFadyen1 Programming Concepts Chapter 4 introduces more advanced OO programming techniques. Construction of a programs usually requires:

Fall 2008 ACS-1805 Ron McFadyen 1

Programming Concepts

Chapter 4 introduces more advanced OO programming techniques.

Construction of a programs usually requires:

•Classes

•Objects

•Methods

•World-level

•Class-level

•Parameters

•Inheritance


Classes An OO program is organized around the concept of class.

For Alice programming, all classes are pre-defined for us.

We choose the classes from the gallery.

(We need other skills to build classes)

If interested, you would explore products: Maya, Max Studio, …

• These are used to construct 3D models

• Building classes is outside the scope of this course

Classes:

• comprise properties, methods, functions


Classes Each class has properties, methods, functions

We can customize … new properties, methods, functions


Objects Showing the relationship amongst classes and objects:

Teacher

fung-yee ron

Student

april joe janet


Methods

Methods define what an object (from the class) can do

• Move, Turn, Roll, etc

• We can’t see the code for these. (The Alice creators don’t want us to change them and they are referred to as primitive methods)

We can customize an object by giving it some new methods

• These you can edit (change)

OO programmers typically use many many methods where each is defined to some fairly simple thing

Methods give us a way of organizing the complexity of our creations

Methods become even more useful when they incorporate parameters


World-level MethodsIf we have a complex method, we can break it up into smaller simpler tasks.

Main idea: take a group of related instructions in one method, place them in a separate method, replace the original lines with a call to the new method

Principle being applied is abstraction – we are now thinking of the group of instructions as a single instruction


Stepwise refinement

When creating an algorithm we can design a solution in terms of solutions to smaller problems. This approach is one where we divide and conquer

we break a task down into a number of sub-tasks, each

of which is described by an algorithm that is smaller and

simpler than that for the entire process.

Each sub-task may require further sub-division until we have divided up the problem into elementary pieces, each of which can be tackled in a simple and straightforward way.


World-level Methods (4-1)Original: Code is placed in a new method:


World-level MethodsOriginal: Revised:

• Original was long, complex

• Revised version more easily understood

Call/invoke/execute the method react


Parameters (4-2)A method is more useful if it can work for different objects

• A robot walks by turning a leg part backward and then forward

• We can place these two “turns” into a method with a parameter … where the parameter specifies the part that “turns”


Parameters

A method with a parameter:

Some original code:


Parameters

Revised:

Original:

An argument supplies a value to be substituted for a method’s parameter … at run time

What different kinds of parameters does Alice allow?


Consider Project 4, Cleanup Robot, page 117

We are told to use 3 methods

… to make it easier to understand a solution

… to make it easier to develop the solution

Put Toys Away

For each toy:

pickup- robot goes and picks up the toy

putInCloset- robot takes the toy to the closet

Example

solution is given in terms of solutions to 2 smaller problems


Example pickup- robot goes and picks up the toy

Robot turns to face the toy

Robot moves toward the toy

Robot picks up toy

putInCloset- robot takes the toy to the closet

Robot turns to face the closet

Closet door opens

Robot moves into the closet

putdown- robot places toy in closet

Robot exits from the closet

Closet door closes

putdown- robot places toy in closet

Robot lowers his arms

Robot releases the toy

Parameters

object; distance to move

object; distance to move

object


Example

Put toys away

pickup putInCloset

putdown

We can represent the overall organization of our methods (i.e. who calls who)


Class-level methods&

3D Models (4-3)

Consider that we have developed new methods (perhaps some new properties and functions too)

In-class example … We can save our object as a new 3D model

… right-click … save object as

… note file type is a2c

Now we, or someone else, could import objects that are created according to that 3D model


Inheritance (4-3)

The new model, Clever Skater, exhibits a feature of OO programming called inheritance

… Clever Skater has methods that were originally part of Ice Skater, along with the new methods we designed

We say Clever Skater inherited those original methods from the Ice Skater model.

Inheritance is a way for us to develop programs or models and share them (i.e. sharing code) with others. Others may use these models exactly as we create them, or they may extend them by changing methods or adding new ones.

This is similar to inheritance in languages like Java … but not exactly …

Documents

Fall 2008ACS-1805 Ron McFadyen1 Programming Concepts Chapter 4 introduces more advanced OO programming techniques. Construction of a programs usually requires: