Karel J. Robot

1. Karel J. Robot A Gentle Introduction to the Art of Object Oriented Programming

2. 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.

4. 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.

5. What’s 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 betweenadjacent 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. 2

6. N Beeper Robot facing east S t r e e t Wall Corner Origin 1st St., 1st Ave. Avenue A Robot in its World

7. 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.

8. 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.

9. 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.

10. 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 robot’s 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.

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

12. Chapter 2 Primitive Instructions and Simple Programs

13. How Do We Tell the Robot What to Do? • We give the robot instructions. • A robot executes an instruction by performing the instruction’s associated action or actions. • The robot executes a program by executing a sequence of instructions that are given to it by the helicopter pilot.

14. 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.

15. 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.

16. 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.

17. 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);

18. 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

19. 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

20. The Complete Program /** * main.java * * Title: Chapter 2 p. 5 * Description: Move a beeper from position 1,4 to position 3,5 * @author Mrs. Houston * @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) { World.setDelay(100); World.readWorld("first.txt"); task(); } }

21. 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.

22. 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.

23. 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.

24. 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

25. 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.

26. 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.

27. 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

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

29. 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(); }

30. 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)

31. 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();

32. 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

33. Bugs and Debugging • In programming jargon, all types of errors are known as “bugs”. • Removing the errors from a program is known as “debugging”.

34. 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.

35. Problems p. 13 • Are there any errors? Does the program complete the task? If not, correct the program. • Find the errors. • What is the smallest program? • Walk around the block. • Get the newspaper • Climb the mountain. • Ripped bag. • Rearrange beepers. • Shuttle race.