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Lecture 9a Instructor: Craig Duckett CALL ME

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Assignment 2 Revision DUE THIS Wednesday, August 5 th Assignment 3 DUE Monday, August 10 th Assignment 3 Revision DUE Monday, August 17 th DUE Monday, August 24 th (NO REVISION) Assignment 4

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Assignment 1 Assignment 1 GRADED Assignment 2 Assignment 2 GRADED Assignment 1 Revision Assignment 1 Revision GRADED Assignment 2 Revision Assignment 2 Revision DUE Lecture 10, Wednesday, August 5 th, by midnight Assignment 3 Assignment 3 DUE Lecture 11, Monday, August 10 th, by midnight Assignment 3 Revision Assignment 3 Revision DUE Lecture 13, Monday, August 17 th, by midnight Assignment 4 Assignment 4 DUE Lecture 15, Monday, August 24 th, by midnight NO REVISION AVAILABLE Extra Credit 01 Extra Credit 01 DUE Lecture 15, Wednesday, August 26 th, by midnight 3 Assignment Announcements

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And Now...... No Quiz Instead

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Mid-Term Exam: Post Mortem Best Class Yet! Class Average was 125 (84%)!

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Lecture 9 Announcements CONTINUED Today A little bit of this, a little bit of that Boolean Expressions and Logical Operators &&, ||, ! Our First Look at Non-Robotic Code (Straight Java, No Chaser) A Word About Static Static Methods vs Public Methods Return Values: What Good Are They and How Do They Work?

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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.

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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 ||).

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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.

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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.

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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

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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 }

Slide 13 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( 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"); }

Slide 14 0 && getStreet() < 11)"> 0 && x < 11) // Testing to see if x is in range of 1 to 10 { System.out.println("X is in range"); } So, r">

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)

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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

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Non-Robotic Java Programming Writing Java programs without using the Becker Robot class or any robots in the code is now deemed non-robotic.

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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).

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The Return Statement and Return Values

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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.

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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

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Two Types of void Nothing goes in, nothing comes out Something goes in, nothing comes out move(); moveMultiple(5); 5 Method 1 Method 2

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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

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WTF? * * Wheres the food? A Sad Scenario

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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()

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A Happy Scenario Breakfast is served!

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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

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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

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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

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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

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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

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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 2 2 2 howManyPrints 2

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Example Code: Return Lets look at some more examples using return NumberTest.java ReturnValues_Demo.java ReturnValues_Demo2.java

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A Word About Static No, not these kinds of static

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public class FileName4 extends Object { public static void main(String[] args) { System.out.println( I printed!"); } } Class Main is going to run whether it contains an instance (object) of a class or not. It is declared static for just such this reasonstatic means that main doesnt need an instance (object) of the class that contains it to be created in order for main to run, because main is set up to be its own instance. In this way, main acts like the starter on a car, it doesnt need a starter to start the starterit is the starter. Interesting note: you can compile your Java program without a main method, you just cant run it! (just like you can build a car without a starter, but you cant start it without the starter). Now, if you are wanting to use other classes (their ideas and attributes) down in main, then you do need to create an instance of those classes ( a named object) that can actually do the something (whatever that something is) that you want done. For instance (pun intended) when we are using the Becker classes, then we need to create a named instance of the Robot class (e.g., a Robot object called Karel OR Jo or Mary) if we want to see any activities and actions done (move, pickThing, putThing, etc). Without the Object doing the actions, then they will only remain ideas Main is going to run whether it contains an instance (object) of a class or not. It is declared static for just such this reasonstatic means that main doesnt need an instance (object) of the class that contains it to be created in order for main to run, because main is set up to be its own instance. In this way, main acts like the starter on a car, it doesnt need a starter to start the starterit is the starter. Interesting note: you can compile your Java program without a main method, you just cant run it! (just like you can build a car without a starter, but you cant start it without the starter). Now, if you are wanting to use other classes (their ideas and attributes) down in main, then you do need to create an instance of those classes ( a named object) that can actually do the something (whatever that something is) that you want done. For instance (pun intended) when we are using the Becker classes, then we need to create a named instance of the Robot class (e.g., a Robot object called Karel OR Jo or Mary) if we want to see any activities and actions done (move, pickThing, putThing, etc). Without the Object doing the actions, then they will only remain ideas but no Object ! What the hay?

Slide 35 " + demo.my_member_variable ); } } This will compile (there is an object called demo to do the action) See Examples: StaticDemo1.java StaticDemo2.java StaticDemo3.java">

public class StaticDemo { int my_member_variable = 99999; public static void main (String args[]) { // Access a non-static member from static method System.out.println ("This generates a compiler error :-( " + my_member_variable); } } This will not compile (there is no object to do the action) public class NonStaticDemo { int my_member_variable = 99999; public static void main (String args[]) { NonStaticDemo demo = new NonStaticDemo(); // Access member variable of demo System.out.println ("This WON'T generate an error! --> " + demo.my_member_variable ); } } This will compile (there is an object called demo to do the action) See Examples: StaticDemo1.java StaticDemo2.java StaticDemo3.java

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Static Method A static method does not need an object to call it. It can call itself ! You there? Im here!

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public class FileName3 extends Object { public static 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 static void main(String[] args) { int num = 0; num = printNum(); //