Objects and Classes: Introduction, Concepts, and Topics for Final Exam

1. Media Software Design DIG 3134 – Lecture 16 Objects and Classes and The Rest of the Course Michael Moshell University of Central Florida (Parts of this lecture are courtesy of Jon Friskics)

2. Our objectives today: 1. Plan the rest of the course 2. Basic object & class concepts Topics for final exam: Databases, plus: Objects: a different way to 'package' software XML: a different way to 'package' information Graphics: creating images with the GD library PDF: creating documents with the tcpdf library CURL: calling other programs and websites Excel: reading and writing Excel files Advanced topics: Recursion, Array sorting, SQL queries

3. Our objectives today: 1. Plan the rest of the course 2. Basic object & class concepts 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

4. Some metaphors 23 scalar variable: a box with something in it (number, string, resource) $x 23 $x $list[1] $list[1] 23 array variable: a cabinet with drawers each drawer has a label (index) $list[2] Joe $list[2] $list[3] 97.2 $list[3]

5. Some metaphors $age['Joe'] 23 associative array: a cabinet with drawers having 'text string' labels $age['Ann'] 64 $age['Joe'] $age['Ann']] $age['Moe'] 97 $age['Moe'] text string: an array of characters The rain in Spain

6. Some metaphors function: a machine with inputs, internal storage and outputs 4 1 numnum $j $result . . . function numnum($k,$n) {var $j, $result; for ($j=1; $j<=$k; $j++) { if ($n==1) $result.="One"; else $result.="Two"; } return $result; }# numnum . . . OneOneOneOne

7. Some metaphors nouns: represent THINGS (information, status) scalars arrays strings verbs: represent ACTIONS (work, algorithm, process) functions

8. Some metaphors functions can contain local variables (not known to outer world) 4 1 This kind of "encapsulation" provides some protection and privacy. Otherwise, my $j is also your $j, and it's a mess! numnum $j $result . . . . . . OneOneOneOne

9. Objects and Classes: Motivation As programs got bigger in the 1970s, programming got MUCH harder. There were spectacular project failures. example: Therac_25 Canadian Radiation Therapy Software design error caused massive overdose, killing patients 50quidsoundboy.net

10. Objects and Classes: Conferences Object Oriented Programs, Systems, Languages and Applications (OOPSLA) – 1986 (Portland, OR) \ - (I attended all the OOPSLAs through 2005) -

11. Objects and Classes: Key Concepts Inheritance and Encapsulation

12. Objects and Classes: Key Concepts Inheritance: A Class Hierarchy Vehicle Automobile Aircraft Boat FixedWing Helicopter Car Truck

13. Objects and Classes: Key Concepts Inheritance: A Class Hierarchy brand: string driver: string Vehicle Automobile tiresize:string licensestate:string licensenumber:string Truck Car nrofwheels:integer length:number nrdoors:integer sunroof:boolean

14. Objects and Classes: Key Concepts Inheritance: A Class Hierarchy brand: string driver: string Vehicle Automobile tiresize:string licensestate:string licensenumber:string Class Truck Car nrofwheels:integer length:number nrdoors:integer sunroof:boolean

15. Objects and Classes: Key Concepts Inheritance: A Class Hierarchy brand: string driver: string Vehicle Automobile tiresize:string licensestate:string licensenumber:string Subclass of 'Vehicle' Truck Car nrofwheels:integer length:number nrdoors:integer sunroof:boolean

16. Objects and Classes: Key Concepts Inheritance: A Class Hierarchy brand: string driver: string Vehicle Automobile tiresize:string licensestate:string licensenumber:string Subclass of 'Automobile' Truck Car nrofwheels:integer length:number nrdoors:integer sunroof:boolean

17. 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 have COMPONENTS like the hardware folks. hytek.in images.yourdictionary.com

18. Encapsulation: Methods You can think of 'traditional' programming with data structures and functions via these metaphors. DATA:bullets FUNCTIONS:guns gunpics.net rt66.com

19. Encapsulation: Methods You can think of 'traditional' programming with data structures and functions via these metaphors. DATA:bullets FUNCTIONS:guns DATA:ingredients FUNCTION:cookers gunpics.net rt66.com 05.com ocdeals.com

20. Encapsulation: Methods You can think of Object Oriented software with objects and their methods, with these metaphors Self-operating weapons: Self-heating MREs: ejogjabelajar.com en.wikipedia.org amazon.com

21. Encapsulation: Methods Example: Traditional $horse=array (0,3,2,4...); function draw($thing) { //loops etc to draw $thing } // MAIN: draw($horse);

22. Encapsulation: Methods 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(); Example: Traditional $horse=array (0,3,2,4...); function draw($thing) { //loops etc to draw $thing } // MAIN: draw($horse);

23. Encapsulation: Methods 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(); horse Draw

24. Encapsulation: Methods 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(); horse Draw horse is an instance of class Animal. Making one is called instantiation.

25. Encapsulation: Methods The methods are really functions that are built into the objects. Like the handle on the hand grenade or the trigger on the land mine or the tear-strip on the MRE horse Draw

26. Encapsulation: Advantages The methods can never get "lost" from the data (in a complex project, or at some later time) because the data and the method are built together. So they are guaranteed to work together. horse Draw

27. Getting Data into Objects • 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.

28. Getting Data into Objects • Properties get defined in a class • class Person { public $firstname, $lastname, $phone, $email; } • Every object instance we create will now contain those four properties

29. Getting Data in and out of Objects • 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.

30. Getting Data in and out of Objects • $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

31. Taking Control of Inputs: private • 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 }

32. 'this' refers to the object itself • 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 } #### Examine the example program: names.php

33. The __construct function • 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,$ln) { if (is_numeric($fn)) print "Class Person does not accept numeric first names like $fn.<br />"; else $this->firstname=$fn; //etc for lastname } #### Examine names2.php

34. islands.php (for study) 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.

35. good2islands.php (challenge problem) Level 3: Write a function to recognize a 2x2 island in the ocean. 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 ...)

36. 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. -36 -