Programming Concepts

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

2
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 our program requires from
  the gallery.
• We need other skills to build classes
• If interested, you would want to learn about
  products such as Maya, Max Studio,
• These products are used to construct 3D models
• Constructing or building classes is outside the
  scope of this course
• Two things that distinguish classes
• Classes are defined to have properties and
  methods (including functions)

3
Classes

• Each class has properties, methods, functions
• We can customize by creating new properties,
  methods, functions

4
Objects

• Showing the relationship amongst classes and
  objects

Student
Teacher
student2
student1
student2
teacher2
teacher1
5
Methods

• Each class/object has a collection of methods
  that define the things an object from that class
  can do
• Move, Turn, Roll, etc
• We cant see the code comprising these. (The
  Alice creators dont want us to change them and
  they are referred to as primitive methods
• We can customize an object by giving it some new
  methods
• you are able to edit those
• 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

6
World-level Methods

• If we have a complex method, we can break it up
  into smaller simpler tasks.
• The main idea is to take a group of related
  instructions in one method, place them in a
  separate method, and replace the original lines
  with a call to the new method
• The principle we are applying is called
  abstraction we are now thinking of the group of
  instructions as a single instruction

7
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.

8
World-level Methods (4-1)

• Original

Code is placed in a new method
9
World-level Methods

• Original

Revised

• Original is long and complex
• The revised version is easily understood
• Note how a method is called

10
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 is used to
  specify the part involved

11
Parameters

• Some original code

• A method with a parameter

12
Parameters

• Original

What different kinds of parameters does Alice
allow?

• Revised

parameters
13
Example

• 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 (storyboard)
• For each toy
• pickup- robot goes and picks up the toy
• putInCloset- robot takes the toy to the closet

solution is given in terms of solutions to 2
smaller problems
14
Example
Parameters
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
object distance to move
object distance to move
object
15
Example
We can represent the overall organization of our
methods (who calls who)
Put toys away
pickup
putInCloset
putdown