Karel%20J.%20Robot

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Karel J. Robot

• A Gentle Introduction to the Art of Object
  Oriented Programming

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Chapter 1

• The
• Robot
• World

3
Modeling a Robot

• Karel J Robot
• A Java class, with a graphical interface, used to
  illustrate concepts we will study in this course.
• We will learn how to write instructions
  (programs) so that our programmable robots can
  perform the tasks we give them.

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The World

• Great flat plane with north, south, east, west
  compass directions.
• Bounded on the west side by an infinitely long
  vertical wall extending northward.
• Bounded on the south by an infinitely long
  horizontal wall extending eastward.
• Streets run horizontally (east-west)
• Avenues run vertically (north-south)
• Streets and avenues have numbers.
• Origin is the corner of 1st street and 1st avenue.

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Whats In The World

• Robots
• Occupy a corner.
• One or more robots can occupy any corner at the
  same time.
• Can face any one of the four compass directions.
• Wall Sections fabricated from the impenetrable
  metal neutronium.
• Positioned between adjacent street corners.
• Block a robots path from one corner to the next.
• Used to represent obstacles, such as hurdles and
  mountains.
• Beepers
• Small plastic cones that emit a quiet beeping
  noise.
• Located on street corners.
• Robots can pick them up, carry them, or put them
  down.

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A Robot in its World
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Fundamental Robot Behaviors

• Robots are mobile.
• Can move forward in the direction it is facing,
  from corner to corner.
• Can turn in place.
• Can turn itself off.
• Robots can detect.
• Walls ½ block in front of them.
• Can hear a beeper only if it is on the same
  corner as one.
• Robots on the same corner with it.

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Fundamental Robot Behaviors

• Robots can navigate by detecting the direction it
  is facing (north, south, east, west).
• Robots can manipulate beepers.
• By carrying them.
• By picking them up, and putting them down.
• By knowing if it is carrying any.

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Tasks

• A task is something that we want a robot to do.
  Some examples are
• Move to the corner of 15th Street and 10th
  Avenue.
• Run a hurdle race (jump over wall sections)
• Escape from an enclosed room that has a door.
• Find a beeper and place it at the origin.
• Escape from a maze.
• Harvest rows of beepers.

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Situation

• A situation is an exact description of what the
  world looks like.
• Situations are specified by a small map or brief
  written description.
• What is each robots current position?
• What is the location and length of each wall
  section in the world?
• What is the location of each beeper in the world?
• See p. 5 for sample situations.

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Problems p. 5

1. Which of the following directions can a robot
   face? Northeast, East, South-Southwest, North,
   164 degrees, Vertical, Down
2. What objects other than robots can be found in
   the robot world?
3. Which of the objects listed in 2 can a robot
   manipulate or change?
4. What reference points can be used in the robot
   world to describe a robots exact location?
5. How many robots can we have in a given robot
   world?

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Chapter 2

• Primitive Instructions and Simple Programs

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How Do We Tell the Robot What to Do?

• We give the robot instructions.
• A robot executes an instruction by performing the
  instructions associated action or actions.
• The robot executes a program by executing a
  sequence of instructions that are given to it by
  the helicopter pilot.

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Fundamental Robot Methods

• Changing position
• move()
• Moves forward one block (faces the same
  direction).
• Will not move forward if it sees a wall section
  or boundary wall between its current location and
  the corner to which it would move.
• Error-shutoff if the path is blocked by a wall.
• turnLeft()
• Pivots 90 degrees to the left (counter-clockwise).
  
• Stays on the same corner.

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Fundamental Robot Methods

• Finishing a Task
• turnOff()
• Robot turns off and is incapable of executing any
  new instructions until restarted on another task.
• Must be the last instruction executed in the
  program.

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Fundamental Robot Methods

• Handling beepers
• pickBeeper()
• Attempts to pick up beeper on the corner it is
  standing and puts it in the beeper bag.
• An error shutoff if no beeper is there.
• If more than one beeper on the corner the robot
  picks up only one.
• putBeeper()
• Attempts to take out a beeper from the beeper bag
  and place it on the corner it is standing.
• An error shutoff if no beeper in the beeper bag.
• If more than one beeper in the beeper bag the
  robot puts down only one.

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Constructing New Robots

• Use the command new
• Give the robot a name.
• Tell the helicopter pilot where to place the
  robot, what direction it should face, and how
  many beepers are in the beeper bag.
• UrRobot karel new UrRobot(1, 2, East, 0)

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The First Task

• Have a robot named Karel transport the beeper
  from 1st Street and 4th Avenue to 3rd Street and
  5th Avenue. After Karel has put down the beeper,
  it must move one block farther north before
  turning off.

Initial Situation
Final Situation
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The Instructions

• task
• UrRobot karel new UrRobot(1, 2, East, 0)
• karel.move()
• karel.move()
• karel.pickBeeper()
• karel.move()
• karel.turnLeft()
• karel.move()
• karel.move()
• karel.putBeeper()
• karel.move()
• karel.turnOff()
• // trace to see
  that it works

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The Complete Program

• /
• main.java
• Title Chapter 2 p. 5
• Description Move a beeper from position 1,4
  to position 3,5
• _at_author Mrs. Houston
• _at_version August 26, 2013
• /
• package kareltherobot
• public class Main implements Directions
• public static void task()
• UrRobot karel new UrRobot(1, 2, East, 0)
• karel.move() karel.move()
  karel.pickBeeper()
• karel.move() karel.turnLeft()
  karel.move()
• karel.move() karel.putBeeper()
  karel.move()
• karel.turnOff()
• // Main entry point
• static public void main(String args)

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Programming Tip

• Always trace the program to determine what the
  program does.
• Simulate the program exactly as the pilot and
  robot would, recording every action that takes
  place.
• Follow the sequences of messages in the order the
  pilot reads them to the robot.
• When
• Trace the program before you type it in.
• Trace the program when it does not perform as
  expected.

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Objects, behavior, and classes

• In Java programming, model elements are called
  objects.
• Objects that share common behavior are grouped
  into classes.
• Defining a class in Java is writing code that
  specifies how objects of the class behave or act.
• Once a class has been defined, objects of that
  class can be created.
• Every object belongs to exactly one class and is
  an instance of that class.
• Predefined objects and classes.
• Java comes with some classes already defined.
• We will also use classes created by other
  programmers.

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Some terminology

• Java uses a reference to identify an object.
• Messages are sent to references, specifying
  behavior with supporting details.
• Reference any phrase that is used to refer to an
  object.
• Messages a request for some desired behavior
  from an object.

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Sending a message

• To send a message, we must specify the object and
  the behavior for that object.
• A reference to the receiver object
• A period
• The message to be sent
• To send a message to a Robot
• karel.move()

reference
message
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Java Syntax Issues

• Special symbols
• Semi-colon Separates one instruction
  from
• the next
• Braces Group blocks of instructions
• Period . Show which instructions belong
  to
• which robot
• Identifiers
• Used for robot and class names.
• Made up of characters (A..Z, a..z), digits
  (0..9), and underscore (_)
• Must start with a character.

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Java Syntax Issues

• Reserved words
• Used to structure and organize primitive
  instructions.
• Their use is reserved for their built-in purpose,
  nothing else.
• Comments
• // single line comments
• / multi line
• comments /
• Provide explanation of what is going on to other
  people who read our programs.

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Look Again At The Program

• task must have one main task block
• UrRobot karel new UrRobot(1, 2, East, 0)
• / delivery instruction (start street, avenue,
  direction, beepers in bag
• all instructions must be given to Karel,
  the only robot in the world /
• karel.move()
• karel.move()
• karel.pickBeeper() // all
  statements must end with a
• karel.move()
• karel.turnLeft() // notice
  the indention
• karel.move() // notice the comments
• karel.move()
• karel.putBeeper()
• karel.move()
• karel.turnOff() //
  always the last statement

Braces must match
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Style Issues

• Programs should be indented nicely.
• Comments should be included.
• Programs should be well organized.
• Programs should be easy to read.

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Example of Poor Indentation

• task UrRobot karel new UrRobot(1, 2, East,
  0)
• karel.move() karel.move()
  karel.pickBeeper()
• karel.move() karel.turnLeft()
  karel.move() karel.move() karel.putBeeper()
  karel.move() karel.turnOff()

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Errors Shutoffs

• Robot turns itself off when it is prevented from
  successfully completing the action associated
  with a message.
• Examples
• Illegal move (path is not clear)
• putBeeper (no beepers in the bag)
• pickBeeper (no beepers on the corner)

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Programming Errors

• Lexical errors
• When a robot encounters an instruction that is
  not part of its vocabulary
• mvoe() instead of move() turnleft() instead of
  turnLeft()
• Yes, capitalization counts Java is case
  sensitive
• Syntax errors
• Use of incorrect grammar or punctuation
• An instruction missing a semi-colon at the
  end. Karel.move()
• Instruction missing () at the end. Karel.move
• Instruction given without a reference.
  move()
• Instruction given without period. Karel
  move()

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Programming Errors

• Execution errors
• Occur whenever a robot in the world is unable to
  execute an instruction successfully and is forced
  to perform an error shutoff.
• Instructing the robot to move when the front is
  blocked.
• Trying to pickBeeper when the corner has no
  beepers.
• Trying to putBeeper when the bag is empty.
• All result in an error shutoff.
• Intent error
• Program seems to run successfully, but does not
  accomplish the task.
• Task pickup the beeper, face north, move one
  block
• Instead, the robot picks up the beeper, and moves
  ahead two blocks

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Bugs and Debugging

• In programming jargon, all types of errors are
  known as bugs.
• Removing the errors from a program is known as
  debugging.

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A Task For Two Robots

• Task Karel is at 3rd street and 1st avenue on a
  corner with a beeper facing east. Jane is at the
  origin facing east. Karel should carry the
  beeper to Jane and put it down. Jane should then
  pick it up and carry it to 1st street and 3rd
  avenue. The beeper should be placed on this
  corner.

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Problems p. 13

1. Are there any errors? Does the program complete
   the task? If not, correct the program.
2. Find the errors.
3. What is the smallest program?
4. Walk around the block.
5. Get the newspaper
6. Climb the mountain.
7. Ripped bag.
8. Rearrange beepers.
9. Shuttle race.