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CH5 – Conditional Statements

Learn about if-else statements and boolean operators in Java programming, explore examples and simplifications.

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CH5 – Conditional Statements

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  1. CH5 – Conditional Statements Flavor 1: if ( <some boolean expression> ) { <some instruction list> } For now: these are method invokations (see next slide) Chapter 5 - IF

  2. IF “predicates” either Tor F frontIsClear(); nextToABeeper(); nextToARobot(); facingNorth(); facingSouth(); facingEast(); facingWest(); anyBeepersInBeeperBag(); if ( ) { … } Robot Let’s check the API to see our options Chapter 5 - IF

  3. Robot Class public class Robot extends UrRobot { public boolean frontIsClear() {…} public boolean nextToABeeper() {…} public boolean nextToARobot() {…} etc… } Now I have a brain! again, you don’t write this class Chapter 5 - IF

  4. Examples if ( karel.frontIsClear() ) { karel.move(); // no danger of hitting wall } if ( karel.anyBeepersInBeeperBag() ) { karel.putBeeper(); //no danger of error } Chapter 5 - IF

  5. Extending Robot public class SmartBot extends Robot { public boolean beeperIsToLeft() {…} public boolean twoBeepersOnCornerOrMore() {…} public void faceEast() {…} } Draw the Inheritance Hierarchy Chapter 5 - IF

  6. MUST put world back in initial situation that it was in BEFORE the method was invoked public boolean beeperIsToLeft() { turnLeft(); move(); if ( nextToABeeper() ) { turnLeft(); turnLeft(); move(); turnLeft(); return true; } turnLeft(); turnLeft(); move(); turnLeft(); return false; } Chapter 5 - IF

  7. you write twoBeepersOnCornerOrMore()it belongs to the SmartBot classnote: you may have to nest if statements Chapter 5 - IF

  8. you write faceEast()it belongs to the SmartBot class Chapter 5 - IF

  9. UrRobot Robot SmartBot Paying Attention? • For the last several slides, I’ve lead you somewhat astray. By now (I’m hoping) someone has pointed out that our Inheritance Structure looks likes this What annoying thing (should have) happened to you while coding the last few examples? Yep, you wrote (or wanted to) turnRight() and maybe even turnAround() AGAIN! ANNOYING! Solution(s)? Chapter 5 - IF

  10. Boolean Operators Karel (Java) Robot (&&, ||, !) • if (! frontIsClear()) { turnLeft(); } move(); Chapter 5 - IF

  11. && and ||(no, I didn’t stutter) Write this method /** * @returns true if there is at least * one beeper on both sides of bot, * false otherwise */ public boolean isBeepOnLeft_And_BeepOnRight() Assume that the class you’re writing this for has SmartBot as its superclass (the one we just suggested). It may help to look at the inheritance tree again. Chapter 5 - IF

  12. IF - ELSE Flavor 2: if ( <boolean expression> ) { <statements> } else { <statements – somewhat different> } Chapter 5 - IF

  13. IF – ELSE Simplifications simplify: if ( frontIsClear() ) { return true; } else { return false; } Chapter 5 - IF

  14. Simplify if (leftIsBlocked() ) { return true; } else { return false; } Chapter 5 - IF

  15. Simplify if ( leftIsBlocked() ) { return false; } else { return true; } Chapter 5 - IF

  16. move(); Simplify – bottom factoring move(); if ( facingSouth() ) { turnLeft(); } else { turnRight(); } if ( facingSouth() ) { turnLeft(); move(); } else { turnRight(); move(); } move(); move(); move(); move(); Chapter 5 - IF

  17. Simplify – top factoring if ( beeperOnLeft() ) { move(); turnLeft(); } else { move(); turnRight(); } Chapter 5 - IF

  18. being redundant again and again and againha ha if ( facingNorth() ) { move(); pickTwoBeepers(); if (facingNorth()) { turnLeft(); } } Chapter 5 - IF

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