Introduction to OOP in VB'NET using Robots

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Introduction to OOP in VB.NETusing Robots

• ACSE Conference, Nov 2004
• Michael Devoy
• Monsignor Doyle C.S.S., Cambridge
• mdevoy_at_look.ca

2
Objectives

• Learn how to introduce OOP within VB.NET using
  Karel the Robot
• Understand the world of Karel the Robot
• Write simple programs to instruct a Robot to
  accomplish a task that involve
• creating a VB.NET application
• declare and create Robot object
• execute methods of a Robot Object
• use inheritance to create smarter types of Robots
• overload and override some of a Robots methods

3
Why Use Robots

• Fun
• Visual
• Early introduction to Object Oriented concepts
• Students start by using objects before needing to
  learn how to build classes
• Teachers dont have to build their own classes
  for students to use
• Free lesson plans and assignments at
  http//csis.pace.edu/bergin/KarelJava2ed/KarelJ
  avaEdition.htmltoc

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When to teach Robots

• Possible in grade 11
• After standard programming expectations have been
  met (variables, if, loops, functions and
  parameters)
• Great introduction to OOP for grade 12
• Reinforces concepts that controls on a form are
  objects with methods and properties
• Answers the question of what should be in a
  module for code re-use
• Great introduction if teaching Java in grade 12

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The World of Robots

• Robots live in a World
• A World has intersections of streets and avenues
• Beepers may be on an intersection
• Robots may pick up or put down Beepers
• Walls may be next to an intersection
• Robots can not walk through Walls (they break)

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Getting Started

• You need
• Windows XP
• Visual Basic.NET (one copy provided free today)
• The kareltherobot.dll file downloaded free from
  the Internet at http//www.acthompson.net/DotNet/K
  arel.htm (click on the here link and copy to
  anywhere you wish on your hard drive)
• The vjslib.dll file downloaded free from the
  Internet at http//msdn.microsoft.com/vjsharp/down
  loads/howtoget/default.aspx (use the 1.1 version)
  and installed into Windows

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Assignment 1 Using Robot methods

• The teacher designs the world layout and poses
  the problem
• The student writes a program that instructs a
  robot (or robots) to complete the task
• For example Write a program that will create a
  robot facing north at corner 1, 6. The robot
  will live in the world found in the file
  fetch.txt. The robot should walk around the
  walls, pick up the Beeper, and return to the
  starting location, facing north.

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Starting Visual Studio.Net

• Start Visual Studio.NET
• Click New Project
• Ensure Visual Basic Project is selected
• Ensure Windows Application is selected
• Browse to a folder to save work in, optionally
  make a new folder, e.g. Robot Assignments
• Enter a name for the project (a new folder will
  be created) e.g. Assignment1

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Starting a VB Program for Robots

• Use Windows Explorer, copy the World file
  fetch.txt and the Robot gifs to the bin
  folder inside your project folder
• Click Project
• Click Add References
• Add references for
• Vjslib.dll
• Kareltherobot.dll

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Add Code Behind the Form

• Access the code editor for the form by double
  clicking the form surface
• Add imports kareltherobot to top of code, to
  allow access to code in kareltherobot.dll
• Add a call to a task sub, inside Form1_Load event
• Start a task sub, by typing private sub task()

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Add Code to Display the World

• Inside the task sub, add the following lines of
  code
• World.readWorld("fetch.txt")
• World.setDelay(20)
• Click the Run button!

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Pattern for Creating a Robot Object

• Dim karel as ur_Robot
• karel new ur_Robot (1, 6, Directions.North, 0)

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Pattern for Calling a Robot Objects Method
The objects name always begins the statement
(karel)

• karel.move()

Dot between object name and method name
Method name always followed by ( ), which may or
may not contain parameters
Other methods a Robot can perform
include turnLeft(), pickBeeper(), putBeeper(),
frontIsClear()
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Your Turn Now

• Complete the code to have the Robot perform its
  task
• Run your program to ensure it functions correctly

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Assignment 2 - Creating a Smarter Robot using
Inheritance

• Inheritance is an important OOP concept
• A new Class is created, based on an existing
  Class
• The existing Class is the parent or base Class
• The new Class is the child or sub Class
• The Child inherits all the Parents attributes
  and methods (except the constructor)
• benefits
• reduces the amount of code we need to write
• makes our program easier to understand
• facilitates the re-use of code
• aids in debugging our program

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A Smarter Robot Problem

• Create a new type of Robot that has the abilities
  to turn right and turn around
• Use this new Robot to solve the same problem as
  Assignment 1
• Our task code should become simpler to write and
  easier to understand

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Starting a new Assignment

• Remain in the same solution
• Close the form and code editing windows
• Click File Add Project New Project
• Ensure Visual Basic Project is selected
• Ensure Windows Application is selected
• Type a name in the name box e.g. Assignment 2
• Click OK
• Right click Assignment 2 in the solution explorer
  window and select set as startup project
• Use Windows Explorer and copy the world file and
  robot gifs to Assignment2s bin folder
• Add the references for vjslib.dll and
  kareltherobot.dll

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Starting a new Class

• Click Project Add Class
• Ensure class is highlighted
• Enter a name for the new class e.g.
  RightTurnerRobot
• Click open

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Pattern to define a Robot child class
RightTurnerRobot is the name of the new Robot
class, a name we choose

• Imports kareltherobot
• Public Class RightTurnerRobot
• Inherits ur_Robot
• Public Sub New (ByVal street As Integer, _
• ByVal avenue As Integer, _
• ByVal direction As Integer, _
• ByVal beepers As Integer)
• MyBase.New(street, avenue, direction,
  beepers)
• End Sub
• ltlt other new methodsgtgt
• End Class

Inherits is the VB keyword to indicate this class
is a child of the ur_Robot class
The constructor method must be named New
MyBase refers to the parent, in this situation
the parents constructor is called
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Pattern for new Method
Public Sub turnRight() turnLeft()
turnLeft() turnLeft() End Sub
Access may be public (available to any class in
your program) or private (available only to
objects of this class)
Parenthesis required after method name, may
contain parameters or be empty
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Your Turn Now

• Complete the turnAround method in the
  TurnRightRobots class
• Edit the code behind the form (refer back to
  Assignment1)
• Make the following changes to the forms code
• Change all ur_Robot to RightTurnerRobot
• Replace multiple calls to turnLeft to turnRight
  and turnAround, as appropriate
• Run your program to ensure it functions correctly

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Assignment 3 Overloading Methods

• To overload a method, means to create a method
  with an existing methods name, but a different
  list of parameters (type or order)
• This is often done with constructor methods, to
  provide a variety of ways of creating an object
  (e.g. specifying beepers in bag or not)
• karel new ur_Robot (1, 6, Direction.North)
• karel new ur_Robot (1, 6, Direction.North, 10)
• move() is a method in the ur_Robot class
• define a new method move(steps) that has a
  parameter that allows us to dictate how many
  steps to move
• we say the move method is now overloaded
• note we can invoke either of the move methods we
  wish, because VB distinguishes between them by
  the parameter list

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A More Flexible Robot Problem

• Create a new type of robot that is a child class
  of the ur_Robot
• This new type of robot can walk multiple numbers
  of intersections with its move method
• This robot will live in the world, as found in
  the file miles.txt
• The robot starts at intersection 2,2
• Use this robot to clean the Beepers in front of
  it
• The robot should stop one intersection past the
  last Beeper
• Our task method should be very easy to read and
  understand

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Starting a new Assignment

• Remain in the same solution
• Close the form and code editing windows
• Click File Add Project New Project
• Ensure Visual Basic Project is selected
• Ensure Windows Application is selected
• Type a name in the name box e.g. Assignment 3
• Click OK
• Right click Assignment 3 in the solution explorer
  window and select set as startup project
• Use Windows Explorer and copy the world file
  (miles.txt) and the robot gifs to Assignment3s
  bin folder
• Add the references for vjslib.dll and
  kareltherobot.dll

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Starting a new Class

• Click Project Add Class
• Ensure class is highlighted
• Enter a name for the new class e.g.
  MileWalkerRobot
• Click open
• Add imports kareltherobot
• Add the constructor

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Pattern for Overloaded Methods
Public Overloads Sub move(byval steps as
Integer) dim x as Integer for x 1 to
steps myBase.move() next End
Sub
Overloads is a VB keyword indicating the
ur_Robots move method is being overloaded a
new move method is being defined with a different
parameter list
myBase.move() executes the move method in the
base class (ur_Robot)
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Your Turn Now

• Complete the move method in the MileWalkerRobots
  class
• Edit the code behind the form (refer back to
  Assignment1)
• Make the following changes to the forms code
• Change all ur_Robot to MileWalkerRobot
• Add the line of code World.setSize(15,15), after
  setting the speed of the animation with the
  World.setDelay(20) method
• Use the new move method to move multiple
  intersections at once
• Move to the first intersection with a Beeper,
  then pick up the Beeper.
• In a similar fashion, move and pick up the second
  Beeper
• Run your program to ensure it functions correctly

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Assignment 4 - Overriding Methods

• To override a method means to replace the
  definition of an existing method, which would be
  inherited from a parent (base) class
• This is accomplished by writing a method
  definition with an identical method signature to
  the method signature in the parent class
• method signature is the method name and parameter
  list
• You can call the parents method, if needed, by
  use of the MyBase keyword

For Example Public Overrides Sub move()
turnLeft() turnRight() myBase.move()
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A Dizzy Robot Problem

• Create a new type of robot that is a child class
  of the ur_Robot
• This new type of robot overrides the move method,
  so that it first turns 3600, then moves forward
  one intersection
• This robot will live in the world, as found in
  the file miles.txt
• The robot starts at intersection 2,2
• Use this robot to clean the Beepers in front of
  it
• The robot should stop one intersection past the
  last Beeper

30
Starting a new Assignment

• Remain in the same solution
• Close the form and code editing windows
• Click File Add Project New Project
• Ensure Visual Basic Project is selected
• Ensure Windows Application is selected
• Type a name in the name box e.g. Assignment 4
• Click OK
• Right click Assignment 4 in the solution explorer
  window and select set as startup project
• Use Windows Explorer and copy the world file
  (miles.txt) and the robot gifs to Assignment4s
  bin folder
• Add the references for vjslib.dll and
  kareltherobot.dll

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Starting a new Class

• Click Project Add Class
• Ensure class is highlighted
• Enter a name for the new class e.g.
  DizzyWalkerRobot
• Click open
• Add imports kareltherobot
• Add the constructor

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Pattern for Overriding Methods
Public Overrides Sub move() Dim i As
Integer For i 1 To 4
turnLeft() Next MyBase.move()
End Sub
Overrides is a VB keyword indicating the
ur_Robots move method is being overridden a
new move method is being defined in the
DizzyWalkerRobot to replace the original move
myBase.move() executes the move method in the
base class (ur_Robot)
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Your Turn Now

• Complete the move method in the
  DizzyWalkerRobots class
• Edit the code behind the form (refer back to
  Assignment3)
• Make the following changes to the forms code
• Change all ur_Robot to DizzyWalkerRobot
• Use multiple move methods to move to the first
  Beeper
• Pick up the Beeper.
• In a similar fashion, move and pick up the second
  Beeper
• Move one more intersection forward
• Run your program to ensure it functions correctly