1. Selected Advanced Topics Chapter 7 and 8
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: int sumOfDigits(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:
MileMover karel = new MileMover(1,1,East,0);
karel.move();
Having a robot set up his own thread, we can do the following:
MileMover karel = 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 karel turnOff

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)