Karel – Primitive Instructions

1. Karel – Primitive Instructions • Basic tools with which all problems are solved (analogies: carpentry, geometry) • move() • turnLeft() • putBeeper() • pickBeeper() • turnOff()

2. OOP -ness • object.method1(); • object.method2(); -where a method acts on the object -objects are typically nouns (e.g., karel) -methods are typically verbs (e.g., move) and represent behavior karel.move()

3. move() • forward only, one block • “Error Shutoff” if trying to move into a wall (a duh! Look first!) Remember C++ and div by zero???

4. turnLeft() • stay at same corner • turn 90 degrees to the left • cannot cause an error shutoff

5. pickBeeper() • picks up beeper on current corner and places in beeper bag • attempted on beeper-less corners causes an error shutoff

6. putBeeper() • take beeper from beeper bag and put down on current corner • attempted with an empty beeper bag causes an error shutoff

7. turnOff() • robot turns off and is incapable of executing another instruction until restarted • the last instruction executed on a robot object

8. Description public class UrRobot { void move() {…} void turnOff() {…} void turnLeft() {…} void pickBeeper() {…} void putBeeper() {…} } • UrRobot class (the “Model-T” Robot) “primitive” You can’t/don’t need to define this class – it is in a library for you to use

9. Sample Program import kareltherobot.*; public class SampleTest implements Directions { public static void main(String args[]) { ur_Robot karel = new UrRobot(2, 1, East, 0); karel.move(); karel.move(); karel.turnLeft(); karel.turnOff(); } static { … // code here that you need not worry much about } }

10. Error Classification • 4-types • lexical error (compiler catches) • word not in its dictionary • syntax error (compiler catches) • incorrect grammar, punctuation, incorrect location of a statement • execution error (run-time environment catches) • can’t perform what you ask (at run-time) • intent error (logic - guess who catches this one!) • program terminates successfully – junk output, however Which is the hardest type of error to correct? Why?

11. Now You Try a Short Program on Paper – 10 minutes • start a robot (HBot) at position (1, 1) (a.k.a, the “origin”) facing North and having an infinite number of beepers • Have the robot “print” (using beepers) the letter H (with 3-beeper sides and a 1-beeper bar) • when done, the robot should be facing North back at the origin (leaving the world in its original state of being)

12. Programming the HBot together • Let’s go into BlueJ and write the HBot. We’ll cover these items: • Your network drive and staying organized • Creating a workspace • Using/reading the API • Compile vs. Execute • www.apcomputerscience.com and setting up things at home