Karel J Robot

1. Karel J Robot Selected Advanced Topics Chapter 7 and 8

2. Recursion • Recursion – where the function being defined is applied within it’s own definition • Ex)(p185) • public void findBeeper() • { if(!nextToABeeper) • { move(); • findBeeper(); • }}

3. Recursion • Recursive functions do not use loops! • Fun Practice: • What is a factorial? • Create the following method: • public static int factorial(int x) • Hints: what does a factorial do? • Takes the number… multiply’s it by the next smallest integer • Stops at 1 • Your method should evaluate whether or not you’ve reached 1

4. Solution • public static int factorial(int x) { if(x<=1) { return 1; } return x*factorial(x-1); }

5. challenge • Create the following method: • intsumOfDigits(int x) • If x is 39, sumOfDigits should return 12 • Hints: base case is a number from 0-9 • For the recursive call, consider how x/10 or x%10 will help • % - modulus – returns the remainder • / - division – doesn’t round: 9/2 = 4

6. Homework • Read chapter 7

7. Thread creation • In the main, we have typically seen the following: • MileMoverkarel = new MileMover(1,1,East,0); • karel.move(); • Having a robot set up his own thread, we can do the following: • MileMoverkarel = new MileMover(1,1,East, 0); • He will do the same thing as above without calling any methods if we have it set up its own thread!

8. Thread creation • Implement the Runnable class //this is a java class that sets up threads • In constructor: • World.setupThread(this) //this tells the robot to run itself • NEED: public void run() • Inside of the run method will be the code that will automatically runj • Lastly – in the main, we need: • World.setTrace(false);World.showSpeedControl(true) • Click resume!

9. Thread creation • Modify the path finding robot from ch 6 pr set so that in the main, you only have the following: • new ch6pr14(2,2,East,0) • //you don’t even have to give the robot a name!

10. 2 different threads • Concurrent threads sometimes pose issues • Homework • Read chapter 8 – program the racers on 212 and the philosophers on 214

11. Problem set • Ch 7, #1(Solve just #16 recursively), 18 • Ch 8, #1 (requires editing steeplechase program) • PACMAN

12. pacman • Our final karel experience: • 1st – set up the robot world to mimic a pacman world (karel images replaces with pacman, etc.) • 2nd – create an abstract class called ghost • Look up the 4 different types of ghosts…. And program their behaviors into different types of classes!

13. Pacman • 3rd – the pacman class • We need to be able to control him • Eventually we will work with keylisteners for seemless play, but for now we’ll do an easier solution • We need a ‘commandPacman()’ method • Creates a local variable: • Scanner kbd = new Scanner(System.in);

14. Pacman • commandPacman() continued… • Need a variable to hold keyboard input: • char move = kb.next().charAt(0); • Need a switch statement so 4 different keys control movements: • switch(move) • { case ‘w’: karel.faceNorth(); karel.move(); break; case ‘s’: karel.faceSouth(); //… you can figure the rest!  Use a while loop so that move == ‘q’ makes karelturnOff

15. Project • Work in pairs! (we will try and mimic teamwork) • 1 person can work on pacman while the other on ghosts • 10 points – working pacman class • 10 points – working ghost classes (i.e. shut off pacman when they touch) • 2 points – accurate world • 3 points – bonus for best version (class will vote)