Note: Original slides provided by www.apComputerScience.com and modified for Mr. Smith

1
Karel Chapter 2 Primitive Instructions
and Simple Programs
Note Original slides provided by
www.apComputerScience.com and modified for Mr.
Smiths AP Computer Science A class
2
Karel - Executing

• The robot executes an instruction by performing
  the instructions associated action or actions
• The robot executes a program by performing a
  sequence of instructions given to it
• Instructions are executed one at a time in the
  order that they are listed

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Karel - Primitive Instructions

• Basic tools with which all problems are solved.
  An analogy is when a carpenter performs primitive
  tasks such as hammering, leveling, measuring,
  sawing, etc. He can accomplish all his carpentry
  tasks (some which are very complicated) using
  these basic tasks.
• In Java, each of these primitive instructions is
  called a method. A standard robot has these five
  methods
• move()
• turnLeft()
• putBeeper()
• pickBeeper()
• turnOff()

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OOP-ness

• object.method1()
• object.method2()
• - A method acts on the object. It is the message
  sent to the object.
• - Objects are typically nouns (e.g., karel).
  They either do things or remember things.
• - Methods are typically verbs (e.g., move) and
  represent behavior
• Example karel.move()

method
object
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move()

• Moves forward one block in the direction that it
  is facing (it will not move sideways)
• Continues to face the same direction
• Error Shutoff if trying to move into a wall or
  boundary (Ouch! Look first!)

6
turnLeft()

• Stays at same corner (does not alter location)
• Turns 90 degrees to the left
• Cannot cause an error shutoff
• Note There is no turnRight() instruction

7
pickBeeper()

• Picks up a single beeper on the current corner
  and places it in beeper bag
• It only picks up one beeper, even if there are
  multiple beepers on the corner
• If attempted on a beeper-less corner, it causes
  an error shutoff

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putBeeper()

• Takes beeper from beeper bag and puts it down on
  current corner
• It only puts down one beeper, even if there are
  multiple beepers in beeper bag
• If attempted with an empty beeper bag, it causes
  an error shutoff

9
turnOff()

• Robot turns off and is incapable of executing
  another instruction until restarted
• This is the last instruction executed on a robot
  object
• After turnOff() is executed, all other
  instructions are ignored

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UrRobot Description

• UrRobot class (the Model-T Robot)

public class UrRobot void move() void
turnOff() void turnLeft() void
pickBeeper() void putBeeper()
primitive You cant/dont need to define this
class it is in a library for you to use
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class

• A class is not a robot. It is a description of
  robots of the same kind.
• The simple model of the robot described above is
  the UrRobot class
• By convention classes begin with a capital letter
• A class is like a production line in a factory
  that makes the same robots

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Sample Client Program

• import kareltherobot.
• public class KarelSample implements Directions
• public static void main(String args )
• UrRobot karel new UrRobot(2, 1, East, 1)
• karel.move()
• karel.move()
• karel.turnLeft()
• karel.putBeeper()
• karel.move()
• karel.turnOff()
• static
• World.setVisible(true)
• World.showSpeedControl(true)

Names for this type of program are Client
program, Driver program, Tester program
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Demo KarelSample
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Coding Conventions

• Classes begin with capital letters (i.e.
  UrRobot). Methods, objects, and variable names
  begin with lower case (camelCase)
• Use indentation to line up statements
• Brackets should be on a line by themselves
• Use comments // to identify what the code is
  supposed to do (very useful)

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Symbols in Java

• A Definition of Symbol A symbol is a written
  word or sequence of characters used to represent
  something else.
• Special symbols . (they mean something
  special in Java)
• Names are symbols karel, UrRobot, putBeeper.
  UrRobot is not a robot itself, but represents a
  type of robot.
• Reserved words are symbols class, void, new
  (they have a built-in purpose)
• Note Symbols must match in case when used in
  Java programs (i.e. karel is not the same as
  Karel and putBeeper is not the same as PutBeeper)

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(Errors are referred to as bugs)
Error Classification

• lexical error (compiler catches)
• word not in its dictionary (i.e. you type MOVE()
  instead of move() )
• syntax error (compiler catches)
• incorrect grammar, punctuation, incorrect
  location of a statement (i.e. leaving out a
  parenthesis or using a colon instead of
  semi-colon)
• execution error (run-time environment catches)
• cant perform what you ask (i.e. error shutoff if
  performing move() when a wall is in the way)
• intent error (logic - guess who catches this
  one!)
• program terminates successfully junk output,
  however (i.e. moving robot to the wrong corner)

Which is the hardest type of error to correct?
Why?
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IDENTIFY THE BUGS (Clue There are at least 9
errors)

• public Class SampleTest implements Directions
• public static void main(String args
• UrRobot karel New UrRobot(2, 1, East, 0).
• karel.move()
• karel.turnLeft()
• getBeeper()
• karel.Move()
• karel.turnOff
• karel.move()

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IDENTIFY THE BUGS SOLUTION

• public class SampleTest implements Directions
• 1) should be class instead of Class
• public static void main(String args) 2) needs
  parentheses
• UrRobot karel new UrRobot(2, 1, East, 0).
• 3) should be new instead of
  New
• 4) use semi-colon instead of period
• karel.move()
• karel.turnLeft() 5) needs a semi-colon on
  end
• karel.pickBeeper() 6) needs an object and is
  named pickBeeper
• karel.move() 7) Move is not a method
• karel.turnOff() 8) needs () (i.e.
  turnOff() )
• karel.move() 9) cant perform move
  after turnOff

public Class SampleTest implements Directions
public static void main(String
args UrRobot karel New UrRobot(2,
1, East, 0).
karel.move() karel.turnLeft()
getBeeper() karel.Move()
karel.turnOff karel.move()
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Now You Try Writing a Short Program to Draw the
Letter H

• Robot starts at origin (1,1), facing north
• Robot draws the letter H
• The bottom of the left bar of the H starts at
  (2,2)
• The H is 5 beepers high
• The middle bar should be 2 beepers between the
  bars
• Robot should return to origin, face north, and
  turn itself off when finished (leaving the world
  in its original state of being

Take a little time to think about the best
approach before jumping into the code. It may
help to sketch the robots path on a sheet of
paper.
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DrawH program Starting Point

• import kareltherobot.
• public class DrawH implements Directions
• public static void main(String args)
• UrRobot karel new UrRobot(1, 1, North,
  infinity)
• // .insert your code here to draw the
  letter H
• static
• World.setVisible(true)
• World.showSpeedControl(true)

Save DrawH.java from my Daily Lesson Plan page
(or Homework page) into your kareltherobot
package in your Karel project. Rename it to
include your full name (i.e. DrawH_JohnDoe)
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DrawH Desired Output
Beginning Situation
Ending Situation
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Starting DrawH together

• Lets go into eclipse and begin writing DrawH.
  Well cover these items
• Your workspace/project/package structure
• Creating (Copying) the DrawH class. Copy the
  starting code from my website.
• Renaming the DrawH class to include your name
  (DrawH_JohnDoe). Click on the DrawH class within
  Package Explorer and select File gt Rename.
• Compiling (save) vs. Executing (run)
• Copying programs between school and home

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Copying Classes between School and Home

• Since there are times when you will want to
  continue your work at home, you will need to be
  able to transfer your code back and forth. This
  is where your flash drive becomes handy.
• To reduce confusion, keep the folder structure on
  your flash drive the same as the folder structure
  on H\workspace.
• Use file manager to locate the Java source file
  (that has extension .java) within the package
  folder.
• Copy only the .java files (not the .class files)
  to your flash drive folder.
• You can then copy these files to your package
  folder on your destination computer.
• Note After you launch eclipse, it is important
  to refresh the project and package. Otherwise,
  the new code may not be seen within eclipse
• Single click on the project and select File gt
  Refresh (or press F5).
• Single click on the package and select File gt
  Refresh (or press F5).