BIT115: Introduction to ProgrammingLecture 13

Instructor: Craig Duckett

Assignment 3

DUE TONIGHT!Uploaded to StudentTracker by midnightIf 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 RevisionDUE Wednesday, March 2nd

3

Assignment 2 Revision GRADED! RETURNED!

Assignment 3 (LECTURE 13) DUE TONIGHTMonday, 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)

Today’s 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

It’s Easy-Peasy!

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.

Topic:

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.

Operator Operation< Less than<= Less than or equal> 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 I’ll 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 won’t 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 OperatorsLogical Operators AND A && B are true only if both A and B are true &&ORA || 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 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: Examplesint 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: Gotchasint 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 comparing—whether variables or methods— listed on both sides of the logical operators.

if( getStreet() > 0 && getStreet() < 11)

Logical Operator: Robotic Examplesif(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.”

Topic:

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

Topic:

Return ValuesAn Illustrated Introduction to Return ValuesFirst, a look at non-return… Up to now we’ve 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 we’ve 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 doesn’t return something back into the program once it’s finished doing whatever it is it’s 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

Return: By Way ofA Cooking Eggs Analogy

customer.overEasy()Alas, nothing is returned.

Hungry customer not happy.

The overEasy() method does exactly what it is supposed to do—it cooks the egg over easy, but that’s as far as it goes…

kitchen classdiningRoom class

WTF? *

* Where’s 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 ScenarioBreakfast 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

int

true

int will be returned

int will be returned

true or false will be returned

chugga-chugga

chugga-chugga

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

2

2

2

howManyPrints

2

Example Code: ReturnLet’s look at some more examples using return…

• NumberTest.java• ReturnValues_Demo.java• ReturnValues_Demo2.java

ICE 14: Logical Operators and Boolean Returns

Before starting today’s ICE, you may want to look at the Boolean return examples:

• BooleanReturns1.java• BooleanReturns2.java• BooleanReturns3.java