Lecture 13 Instructor: Craig Duckett CALL ME Assignment 3 DUE TONIGHT! Uploaded to StudentTracker by midnight If you are submitting as part of a team make sure that all team member names are on both the.java program and.doc summary files. Also only one member of the team has to submit, but I will return the graded assignment to all members of the team. Assignment 3 Revision DUE Wednesday, March 2 nd 3 Assignment 2 Revision GRADED! RETURNED! Assignment 3 (LECTURE 13) Monday, February 22 Assignment 3 Revision (LECTURE 16) Wednesday, March 2 Assignment 4 (LECTURE 19) Monday, March 14 NO REVISION Extra Credit 01 (LECTURE 20) Wednesday, March 16 Assignment Dates (By Due Date) Todays Topics Boolean Expressions and Logical Operators &&, ||, ! Our First Look at Non-Robotic Code (Straight Java, No Chaser) Return Values: What Good Are They and How Do They Work? And Now:... The Warm-Up Quiz Boolean Expressions and Logical Operators A Boolean Expression is an expression that results in a Boolean value, that is, in a value that is either true or false. More complex Boolean expressions can be built out of simpler expressions, using the Boolean Logical Operators. Boolean Expressions and Comparison Operators Using Comparison Operators, the test in if and while statements are Boolean expressions that give a true or false answer to a question. So far, our questions have been simple. As our programming skills grow, however, we will want to ask more complex questions, which will need more complex Boolean expressions to answer. OperatorOperation < Less than Greater than >= Greater than or equal == Equal != Not equal Just like the mathematic operators ( + - / * ) can be combined to form more complex expressions like s = (( x + y) * (w z)) / 2 so too can Boolean expressions be combined to create more complex and utility expressions using and (represented by &&) and or (represented by ||). Logical Operators: && (And) and II (Or) In many programming languages like Java, JavaScript, C++, and C# the logical operators and and or are represented in the code by a double ampersand && and double pipe || And && Double Ampersand Or || Double Pipe There is also the not operator represented by a single exclamation point ! which Ill talk about in a moment. Not ! Single Exclamation Point Java also has a single & and single | characters, called bitwise operators, but for the purposes of this course we wont be discussing them. These will come a bit later (pun intended) along your journey in learning programming languages. Where is the pipe character | located on the keyboard? Before We Continue: What Pipe Character ? AN INTERESTING NOTE : The pipe character goes by several different names, depending on the particular group using it: besides being called the pipe, it can also be called the pipeline, vertical bar, Sheffer stroke, polon, verti-bar, vbar, stick, vertical line, vertical slash, bar, or glidus. Logical Operators AND A && B are true only if both A and B are true && OR A || B are true if A is true or B is true or they're both true || NOT !A is the opposite of A. If A is true, then !A is false. If A is false, !A is true. ! && || TRUE TRUE TRUE TRUE FALSE FALSE TRUE FALSE TRUE FALSE TRUE FALSE FALSE TRUE TRUE FALSE FALSE FALSE AND Operator OR Operator The double ampersand && and double pipe || are called short circuit logical operators Logical Operator: Examples int a = 7; int b = 10; if( a > 4 && b < 20 ) { // This will be true since both operands to the && operator will evaluate to true } int c = 10; int d = 40; if( c == 7 || d > c ) { // This will be true. Even though the first operand evaluates to false, // the second will evaluate to true. } int e = 7; int f = 10; if( !(e == f) ) { // This will evaluate to true since e == f will be false, // and the NOT operator will reverse it } Logical Operator: Gotchas int x = 5; if( 0 < x < 11) // Testing to see if x is in range of 1 to 10 { System.out.println("X is in range"); } int x = 5; if( x > 0 && < 11) // Testing to see if x is in range of 1 to 10 { System.out.println("X is in range"); } Logical Operator: Gotchas int x = 5; if( x > 0 && x < 11) // Testing to see if x is in range of 1 to 10 { System.out.println("X is in range"); } So, remember: you need whatever you are comparingwhether variables or methods listed on both sides of the logical operators. if( getStreet() > 0 && getStreet() < 11) Logical Operator: Robotic Examples if(this.countThingsInBackpack() > 0 && this.frontIsClear()) { this.putThing(); this.move(); } if((this.isFacingEast() || this.isFacingWest()) && this.frontIsClear()) { this.move(); } if( !(this.frontIsClear()) ) { this.turnLeft(); } Example: LogicalOperatorRobot.java Non-Robotic Java Programming Writing Java programs without using the Becker Robot class or any robots in the code is now deemed non-robotic. Start Looking for Non-Robotic Java* Straight Java, No Chaser * Of course any new topics we learn under the heading Non-Robotic Java can still be used when working with Robots, like Return Values and Static Methods, as we will see Example: LogicalOperatorsExample.java Starting today, we will begin introducing Non-Robotic Java into the mix, which will find its way into the PowerPoint slides, some of the example code, several of the ICEs, and even one of the Assignments, Assignment 4 (Advanced). The Return Statement and Return Values Return Values An Illustrated Introduction to Return Values First, a look at non-return Up to now weve seen how to use void methods public void moveMultiple(int numberOfIntersections) { int counter = 0; while( counter < numberOfIntersections) { this.move(); counter = counter + 1; } rob.moveMultiple(5); You can pass an argument to a void method and it will do whatever it is meant to do, but nothing is returned as a separate value that the program might use later on. Void: Means Nothing is Returned Up to now weve seen how to use void methods. public void moveMultiple(int numberOfIntersections) { int counter = 0; while( counter < numberOfIntersections) { this.move(); counter = counter + 1; } void means that nothing is returned back to the program; the method does something, it just doesnt return something back into the program once its finished doing whatever it is its been doing. moveMultiple 5 and down in main: rob.moveMultiple(5); The meaning of void Two Types of void Nothing goes in, nothing comes out Something goes in, nothing comes out move(); moveMultiple(5); 5 Method 1 Method 2 Cooking Eggs Analogy Return: By Way of A Cooking Eggs Analogy customer.overEasy() Alas, nothing is returned. Hungry customer not happy. The overEasy() method does exactly what it is supposed to doit cooks the egg over easy, but thats as far as it goes kitchen class diningRoom class WTF? * * Wheres the food? A Sad Scenario Cooking Eggs Analogy plate = customer.overEasy() Hooray, overEasy() returns the cooked egg and puts it in the plate! Plate is now used to transport egg to happy customer! egg.sunnySideUp() egg.overEasy() egg.overMedium() egg.overHard() egg.scrambled() egg.poached() egg.hardboiled() egg.softBoiled() A Happy Scenario Breakfast is served! Return: The Return Type Must Be Specified The Return Value is a way to send the information back into the program so the program can use it in another way. public int addSum(int num) public int countMoves( ) return counter; return sum; public boolean isNorth(int num) return true; int true int will be returned true or false will be returned chugga-chugga Nothing goes in, something comes out Something goes in, something comes out FileName.java FileName2.java 3 Method 1 Method 2 Two Types of Return class PrintHelper extends Object { public int printNum() { System.out.println("Going to print, some number of times!"); int howManyPrints = 0; while(howManyPrints < 2) { System.out.println("Printing!"); howManyPrints++; // This is a basic counter } return howManyPrints; } } public class FileName extends Object { public static void main(String[] args) { PrintHelper Gutenberg = new PrintHelper(); int num; num = Gutenberg.printNum(); // This method is called by an object System.out.println( "The method printed " + num + " times!"); } } Walkthrough: FileName.java class PrintHelper extends Object { public int printNum() { System.out.println("Going to print, some number of times!"); int howManyPrints = 0; while(howManyPrints < 2) { System.out.println("Printing!"); howManyPrints++; // This is a basic counter } return howManyPrints; } } public class FileName extends Object { public static void main(String[] args) { PrintHelper Gutenberg = new PrintHelper(); int num; num = Gutenberg.printNum(); System.out.println( "The method printed " + num + " times!"); } } Class Idea / Attributes Object (Instance of Class) Class class PrintHelper extends Object { public int printNum() { System.out.println("Going to print, some number of times!"); int howManyPrints = 0; while(howManyPrints < 2) { System.out.println("Printing!"); howManyPrints++; // This is a basic counter } return howManyPrints; } } public class FileName extends Object { public static void main(String[] args) { PrintHelper Gutenberg = new PrintHelper(); int num = 0; num = Gutenberg.printNum(); System.out.println( "The method printed " + num + " times!"); } } howManyPrints num class PrintHelper extends Object { public int printNum () { System.out.println("Going to print, some number of times!"); int howManyPrints = 0; while(howManyPrints < 2) { System.out.println("Printing!"); howManyPrints++; // This is a basic counter } return howManyPrints; } } public class FileName extends Object { public static void main(String[] args) { PrintHelper Gutenberg = new PrintHelper(); int num; num = Gutenberg.printNum(); System.out.println( "The method printed " + num + " times!"); } } howManyPrints num howManyPrints 2 Example Code: Return Lets look at some more examples using return NumberTest.java ReturnValues_Demo.java ReturnValues_Demo2.java ICE 14: Logical Operators and Boolean Returns Before starting todays ICE, you may want to look at the Boolean return examples: BooleanReturns1.java BooleanReturns2.java BooleanReturns3.java