1 DIG 3134 – Lecture 16 Objects and Classes and The Rest of the Course Michael Moshell University...

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DIG 3134 – Lecture 16

Objects and Classesand

The Rest of the Course

Michael MoshellUniversity of Central Florida

(Parts of this lecture are courtesy of Jon Friskics)

Media Software Design

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Our objectives today:1. Plan the rest of the course2. Basic object & class concepts

Topics for final exam: Databases, plus:

Objects: a different way to 'package' softwareXML: a different way to 'package' informationGraphics: creating images with the GD library

PDF: creating documents with the tcpdf libraryCURL: calling other programs and websitesExcel: reading and writing Excel files

Advanced topics: Recursion, Array sorting, SQL queries

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Strategy for Final Exam: Database, plus (6-choose-5).Each question will look approximately like this:

Level 1 (60%) read and hand-simulate small program

Level 2 (+20%) answer a conceptual question

Level 3 (+20%) write or repair a small program

Our objectives today:1. Plan the rest of the course2. Basic object & class concepts

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Some metaphors

23$x scalar variable:a box with something in it(number, string, resource)

$x

$list[1]

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23 array variable:a cabinet with drawerseach drawer has a label(index)

$list[2]

$list[3]

$list[1]

Joe$list[2]

97.2$list[3]

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$age['Joe'] 23 associative array:a cabinet with drawershaving 'text string' labels

$age['Ann']]

$age['Moe']

$age['Joe']

64$age['Ann']

97$age['Moe']

text string:an array of characters

The rain in Spain

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

T h e r a i n i n S p a i n

Some metaphors

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function:a machine with inputs,internal storage andoutputs

function numnum($k,$n){var $j, $result;

for ($j=1; $j<=$k; $j++){ if ($n==1) $result.="One"; else $result.="Two";}return $result;

}# numnum

$j

$result . . .

. . .numnum

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OneOneOneOne

Some metaphors

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nouns: represent THINGS (information, status)

scalarsarraysstrings

verbs: represent ACTIONS (work, algorithm, process)

functions

Some metaphors

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functions can contain local variables (not known to outer world)

$j

$result . . .

. . .numnum

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OneOneOneOne

This kind of"encapsulation"provides someprotection andprivacy.

Otherwise, my $jis also your $j, andit's a mess!

Some metaphors

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Objects and Classes:Motivation

As programs got bigger in the 1970s, programming got MUCH harder.There were spectacular project failures.

example:

Therac_25 Canadian RadiationTherapy

Software design error causedmassive overdose,killing patients 50quidsoundboy.net

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Objects and Classes:Conferences

Object Oriented Programs, Systems, Languages and

Applications (OOPSLA) – 1986 (Portland, OR)\

- (I attended all the OOPSLAs through 2005) -

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Objects and Classes:Key Concepts

Inheritance and Encapsulation

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Inheritance: A Class Hierarchy

Vehicle

Automobile Aircraft Boat

HelicopterFixedWing

Car Truck

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Vehicle

Automobile

Car Truck

brand: stringdriver: string

tiresize:stringlicensestate:stringlicensenumber:string

nrofwheels:integerlength:number

nrdoors:integersunroof:boolean

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Vehicle

Automobile

Car Truck





Class

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Vehicle

Automobile

Car Truck





Subclass of'Vehicle'

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Vehicle

Automobile

Car Truck





Subclass of'Automobile'

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Inheritance: Advantages

The superclass can contain attributes (values) and methods(functions) that can be used by lots of subclasses.

This greatly enhances RE-USE and holds down costs.

The "dream" of software design is to be able to haveCOMPONENTS like the hardware folks.

hytek.in

images.yourdictionary.com

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Encapsulation: Methods

You can think of 'traditional' programming with data structuresand functions via these metaphors.

DATA:bullets FUNCTIONS:guns

gunpics.net

rt66.com

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You can think of 'traditional' programming with data structuresand functions via these metaphors.

DATA:bullets FUNCTIONS:guns

DATA:ingredients FUNCTION:cookers

gunpics.net

rt66.com

ocdeals.com

05.com

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You can think of Object Oriented software with objectsand their methods, with these metaphors

Self-operating weapons:

Self-heating MREs:

en.wikipedia.org

ejogjabelajar.com

amazon.com

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Example: Traditional

$horse=array (0,3,2,4...);

function draw($thing){ //loops etc to draw $thing}

// MAIN:draw($horse);

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Example: Traditional

$horse=array (0,3,2,4...);

function draw($thing){ //loops etc to draw $thing}

// MAIN:draw($horse);

Example: OO

class GraphicObject{ public function draw()

{ // details }}class Animal extends

GraphicObject{ // details of animals }

// MAIN:$horse=new Animal(0,3,2,4...);

$horse->draw();

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Encapsulation: MethodsExample: OO





$horse->draw();

horse

Draw

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Encapsulation: MethodsExample: OO





$horse->draw();

horse

Draw

horse is an instance of class Animal.Making one is called

instantiation.

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The methods are reallyfunctions that arebuilt into the objects.

Like the handle on the hand grenade

or the trigger on the land mine

or the tear-strip on theMRE

horse

Draw

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Encapsulation: Advantages

The methods can neverget "lost" from the data

(in a complex project, orat some later time)

because the data and themethod are built together.

So they are guaranteedto work together.

horse

Draw

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– Variables inside objects are called properties

– Properties are very similar to variables, but they have special OOP-related controls ("safety covers")

– Visibility: 3 kinds of Properties

• Public – global property – can be accessed anywhere

• Private – property can only be accessed from within the enclosing class

• Protected – property can only be accessed from within either the

enclosing class or any subclasses.

Getting Data into Objects

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– Properties get defined in a class

– class Person {

public $firstname,

$lastname,

$phone,

$email;

}

– Every object instance we create will now contain those four properties

Getting Data into Objects

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– Once properties are defined, you can access them with PHP’s object notation

• $person1 = new Person();

print "who?".$person1->firstname. " ".

$person1->lastname;

Prints who?

because we haven't yet put anything into the properties.

Getting Data in and out of Objects

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$person1 = new Person();

Because the properties are declared as public, we can put data into the object the same way (no safety controls)

$person1->firstname = “Jonathon”;

$person1->lastname = “Seagull”;

print "who? ".$person1->first_name. " ".

$person1->last_name;

Prints who? Jonathan Seagull

Getting Data in and out of Objects

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– Here's how a class can protect itself.

class Person{

private $firstname;

private $lastname;

public function setnames($fn,$ln)

{

if (is_numeric($fn))

print "Class Person does not accept numeric first names

like $fn.<br />";

else

$this->firstname=$fn;

//etc for lastname

}

Taking Control of Inputs: private

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– Here's how a class can protect itself.

class Person{

private $firstname;

private $lastname;

public function setnames($fn,$ln)

{



like $fn.<br />";

else


//etc for lastname

}

#### Examine the example program: names.php

'this' refers to the object itself

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– You can automate part of the new-object-creation process:

class Person{

private $firstname;

private $lastname; // NOTE the two underscores __ at beginning

public function __construct($fn,$ln)

{



like $fn.<br />";

else


//etc for lastname

}

#### Examine names2.php

The __construct function

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Compare it to the starter kit for Battleship

Same kind of loops (without the Visible array)

but it uses a Class, with Properties and Methods

STUDY LEVELS:

Level 1: Hand simulate the private function 'goodisland'

Level 2: Explain a command like:

$color=$this->grid[$i][$j];

What means 'this'? What data does 'grid' refer to? Why not $grid?

What means "private function"?

What does 'print_r' do?

Level 3: Write a function recognize a 2x2 island in the ocean.

islands.php (for study)

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Level 3: Write a function to recognize a 2x2 island in the ocean.

good2islands.php (challenge problem)

Specifically, good2island($x,$y) returns TRUE if ($x,$y) is pointing to

one of the four black squares that constitute a 2x2 black block

entirely surrounded by white squares.

I have provided a mini-essay on problem solving (on the course website)

that walks through a solution to this problem.

Level 4: Use good2island to COUNT the 2x2 islands in the ocean....

(It's easier than it may seem at first glance ...)

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FOR THURSDAY:The usual shoot-out model:GET your Group's BEST GAME ready to play!

If you need help with Project 3, come SEE ME.

1 DIG 3134 – Lecture 16 Objects and Classes and The Rest of the Course Michael Moshell University...

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