Object Oriented Programming with PHP

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Object Oriented Programming with PHP Jussi Pohjolainen

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Intro to OO • Object Oriented programming is a programming paradigm • PHP is a multi-‐paradigm programming language • OO is the most popular paradigm today and it's used in most of the languages • Java • C# • C++ • Swift ...

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OO Benefits • Reusability • Code can be reused • Management • Better management by coding classes and objects that communicate with each other • Maintanence • When changing code, it does not influence the whole app

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Basic Concept: Object • In real life, the world consists of objects: • cars, buildings, trees, ships, humans, flowers.. • Every object has actions (=methods!) that can incluence other objects • jack drives ferrari. • Object jack has a method drive that influences some way to object ferrari. • In OO, you should implement the app so that it consists of objects that influence each other!

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Example about an Object • Datsun 100A is an object • Datsun 100A has different actions or methods: • drive • brake • park... • Datsun 100A has information or attributes: • color • amount of gears • amount of doors...

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Basic Concept: Class • Class is a blueprint or template of an object • Class describes the state and behaviour to it's objects. • Object is created from the class.

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Examples: Class to Object Class Object Car datsun 100a Human Jack Bauer Color red Laptop MacBook Pro String "some string" Array {1,2,3,2,4} ... ...

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Different Objects Datsun 100A Datsun 100A Tesla Model S Tesla Model S Škoda Superb Škoda Superb

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Objects datsun, tesla, škoda • datsun • brand: "Datsun 100A" , horsePower: 45, fuzzy dices: true, color: {255,0,0} • tesla • brand: "Tesla Model S", horsePower: 700, fuzzy dices: false, color: {255,0,0} • škoda • brand: "Škoda Superb Combi", horsePower 120, fuzzy dices: true, color: {255,255,255}

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Car's Blueprint (Class) in UML Car brand motor amountOfDoors color hasFuzzyDices . .

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From Class to Object datsun Datsun 100A 1.0 3 red true lambo Lamborghini Diablo 8.0 3 red false Car brand motor amountOfDoors color hasFuzzyDices . .

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Car-‐class, extension Car brand motor amountOfDoors color hasFuzzyDices drive park brake

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PHP and OO

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Person firstname lastname age profession phonenumber eat sleep drinkBeer Person – class to PHP class Person { public $firstname; public $lastname; public $age; public $profession; public $phonenumber; function eat() { print "Eating"; } function sleep() { print "Sleeping"; } function drinkBeer() { print "Drinking Beer"; } }

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From Class to Object class Person { public $firstname; public $lastname; function drinkBeer() { print "Drinking Beer"; } } $jack = new Person(); $jack-‐>firstname = "Jack"; $jack-‐>lastname = "Bauer"; $jack-‐>drinkBeer();

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Creating Objects From the Class class Car { public $brand; public $amountOfGas; function drive() { $this-‐>amountOfGas-‐-‐; } } $ferrari = new Car(); $ferrari-‐>brand = "Ferrari California"; $ferrari-‐>amountOfGas = 100; $ferrari-‐>drive(); print $ferrari-‐>amountOfGas;

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Basic Concept -‐ Encapsulation private public method

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About Attributes • Attributes are usually marked as private • The reason for this is that other objects cannot change the values as they will • You don't for example want that every object in the world can change person's weight to 500kg...

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Cannot Access Private class Person { private $name; private $weight; } $jack = new Person(); $jack-‐>name = "Jack Bauer"; > php Person.php Fatal error: Cannot access private property Person::$name in /path/to/Person.php on line 10

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class Person { private $name; private $weight; function setName($name) { if(is_string($name) && strlen($name) >= 3) { $this-‐>name = $name; } } function getName() { return $this-‐>name; } function setWeight($weight) { if(is_numeric($weight) && $weight > 0 && $weight <= 500) { $this-‐>weight = $weight; } } function getWeight() { return $this-‐>weight; } } $jack = new Person(); $jack-‐>setName("Jack Bauer"); $jack-‐>setWeight(80); $jack-‐>setWeight(-‐80); $jack-‐>setWeight("Just testing"); print $jack-‐>getWeight(); // 80

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References

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Passing Objects jack = new Person(); $jack-‐>setName("Jack Bauer"); $jack-‐>setWeight(80); $jack-‐>setWeight(-‐80); $jack-‐>setWeight("Just testing"); print $jack-‐>getWeight(); // 80 $john = $jack; print $john-‐>getWeight(); // ?? $jack-‐>setWeight(90); print $jack-‐>getWeight(): // ??

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Value vs Reference • PHP5 basic types are by default passed by value • When doing this on basic types, like ints: • $a = $b; // $b integer value is copied to $a • Objects are passed by reference • When doing this on objects • $a = $b; // $b memory address is copied to $a

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Constructor/Destructor

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Constructors • Constructor is a init method that is called when an object is created • PHP 5 does not provide default constructor, like in other languages • Constructor method has a special name in PHP • __construct() • Constructor usually initializes class members, attributes

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Example class Person { private $name; function __construct($name) { $this-‐>name = $name; } } $jack = new Person("Jack Bauer");

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Destructor class Person { private $name; function __construct($name) { $this-‐>name = $name; print "Creating " . $this-‐>name . "\n"; } function __destruct() { print "Destroying: " . $this-‐>name . "\n"; } } $jack = new Person("Jack Bauer");

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Composition

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Composition • Relationship between objects, where one object owns, or has the other object • Example • Car has or owns Motor • When Car is build, it's motor is built also • When Car is destroyed it's motor is detroyed • Composition can be one to one or one to many

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class Motor { function __construct() { print "Motor!\n"; } function __destruct() { print "Motor is killed\n"; } } class Car { private $motor; function __construct() { print "Car!\n"; $this-‐>motor = new Motor(); } function __destruct() { print "Car is killed\n"; } } $c = new Car();

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class Professor { function __construct() { print "Professor was created!\n"; } function __destruct() { print "Professor is deleted\n"; } } class Department { private $professors; function __construct($professor) { $this-‐>professors = array(); $this-‐>professors[] = $professor; print "Deparment was created\n"; } function addProfessor($professor) { $this-‐>professors[] = $professor; } function __destruct() { print "Department is deleted\n"; } } $deartment = new Department(); $tina = new Professor(); $jack = new Professor(); $department-‐>addProfessor($tina); $department-‐>addProfessor($jack);

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About Types

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PHP Types • Single data type (Scalar) • boolean • integer • float • string • Compound type • array • object • Special types • resource • NULL

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PHP Types // SCALAR types $integer = 1; $float = 1.1; $boolean = true; $string = "moi"; // COMPOUND types class Person { } $array = [1,2,3,4]; $object = new Person(); // SPECIAL types $resource = // some link to external resource $null = NULL;

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Inheritance

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Introduction to Inheritance • Relationship between two more classes where derived class inherites • methods • attributes • .. of pre-‐existing base classes • Intended to help reuse of existing code with little or no modification

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UML Employee Programmer salary (int) implementApp() setSalary(int) getSalary() : int

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Example class Human { function eat() { print "Eating healthy!"; } } class Programmer extends Human { function code() { print "Coding!"; } } $tina = new Programmer(); $tina-‐>eat(); $tina-‐>code();

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Inheritance can be continous • Derived class can inherit another class, which inherits another class and so on • Mammal <-‐ Human <-‐ Worker <-‐ Programmer • When changing the base class all the derived classes change also!

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Example: JFrame on Java

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Multiple Inheritance: NOT supported in PHP5 Driver TaxiDriver licenceID : string yearsOfApproval : int areaCode : int Conductor accountNumber : int What would be a possible problem in multi-‐inheritance?

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Visibility • public • Visible in base class, derived classes and world • protected • Visible in base class and derived classes • private • Visible only in base class

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Public class Human { public function drinkCoffee() { print "Drink coffee"; } } class Programmer extends Human { public function codeApps() { $this->drinkCoffee(); print "Code apps"; } } $jack = new Programmer(); $jack->drinkCoffee(); // "Drink Coffee" $jack->codeApps(); // "Drink Coffee Code Apps"

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Private class Human { private function drinkCoffee() { print "Drink coffee"; } } class Programmer extends Human { public function codeApps() { $this->drinkCoffee(); // Can't access because private print "Code apps"; } } $jack = new Programmer(); $jack->drinkCoffee(); // Can't access because private $jack->codeApps();

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Protected class Human { protected function drinkCoffee() { print "Drink coffee"; } } class Programmer extends Human { public function codeApps() { $this->drinkCoffee(); // Success, "Drink Coffee" print "Code apps"; } } $jack = new Programmer(); $jack->drinkCoffee(); // Can't access $jack->codeApps(); // "Drink Coffee Code Apps"

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What now? class Person { } $jack = new Person(); $jack-‐>name = "Jack Bauer"; > php Person.php >

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Dynamic Properties class Person {} $jack = new Person(); // In PHP you can add dynamic properties! $jack->name = "Jack Bauer"; print $jack->name;

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Dynamic Properties class Person { private $name = ""; } class Programmer extends Person { } // Jack now does not have $name, it does not // know anything about it. $jack = new Programmer(); // We are adding a NEW property to programmer! // This can be very confusing! $jack->name = "Jack Smith"; print $jack->name; // Outputs "Jack Smith"

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Basic Inheritance Person Programmer name (string) salary (int) implementApps() beNerd() sleep() drink() eat()

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Overriding Person Programmer name (string) salary (int) implementApps() beNerd() drink() eat() sleep() drink() eat()

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Example class Person { function eat() { print "Eating healthy!"; } } class Programmer extends Person { function eat() { print "Eating pizza!"; } } $tina = new Programmer(); $tina-‐>eat();

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parent class Person { public $name; function printInfo() { print "name = " . $this-‐>name . "\n"; } } class Programmer extends Person { public $salary; function printInfo() { parent::printInfo(); print "salary = " . $this-‐>salary . "\n"; } } $tina = new Programmer(); $tina-‐>name = "Tina"; $tina-‐>salary = 4000; $tina-‐>printInfo();

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parent and constructors class Person { private $name; function __construct($name) { $this-‐>name = $name; } function __toString() { return $this-‐>name . "\n"; } } class Programmer extends Person { private $salary; function __construct($name, $salary) { parent::__construct($name); $this-‐>salary = $salary; } function __toString() { return parent::__toString() . $this-‐>salary . "\n"; } }

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Abstract Class

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Abstract Class • Abstract class is class which you cannot instantiate (create objects) • It's possible to inherite abstract class and create objects from the inherited class, it it is concrete one • Abstract class may have abstract methods that do not have implementations • Abstract methods must be implemented in derived classes

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Example <> Mammal Elephant name (string) trunkLength (int) makeSound() makeSound {abstract}

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Code abstract class Mammal { abstract function makeSound(); } class Elephant extends Mammal { public function makeSound() { print("Pruuut!"); } } // $m = new Mammal(); $e = new Elephant(); $e->makeSound();

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abstract class Shape { public $x; public $y; abstract function surfaceArea(); } class Circle extends Shape { public $radius; public function surfaceArea() { return pi() * $this->radius * $this->radius; } } class Rectangle extends Shape { public $width; public $height; public function surfaceArea() { return $this->width() * $this->height; } } $c = new Circle(); $c->x = 50; $c->y = 50; $c->radius = 3; print ($c->surfaceArea());

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Interface • Interface is a abstract class that holds only abstract methods • Class can implement several interfaces • Class can inherite only one class

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Code interface MovingObject { public function move(); } class Car implements MovingObject { public function move() { print "Car is moving"; } } $c = new Car(); $c->move();

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Code interface MovingObject { public function move(); } interface RunsOnGasoline { public function addMoreGasoline(); public function reduceGasoline(); } class Car implements MovingObject, RunsOnGasoline { public function move() { print "Car is moving"; } public function addMoreGasoline() { ... } public function reduceGasoline() { ... } } class Mammal {} class Human extends Mammal implements MovingObject { public function move() { print "Human is moving"; } }

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Polymorphism

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Problem doSomething(array(1,2,3)); doSomething(4); doSomething(4.5); function doSomething($a) { print($a[0]); }

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Type Declarations • Force function parameters to be certain type • If not, error is generated • Valid types in PHP5 • class/interface, self, array, callable • Valid types in PHP7 • In addition to the previous, bool, float, int string

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Type Declaration doSomething(array(1,2,3)); doSomething(4); // WILL FAIL doSomething(4.5); // WILL FAIL function doSomething(array $a) { print($a[0]); }

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Type Declaration class Human { public function move() { print "Human is moving"; } } doSomething(new Human()); function doSomething(Human $a) { $a->move(); } Now you can pass only Human objects!

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class Mammal { public $name; public function move() { print "$this->name is moving\n"; } } class Dog extends Mammal { public function bark() { print "$this->name is barking\n"; } } class Human extends Mammal { public function createArt() { print "$this->name is creating art\n"; } } $human = new Human(); $human->name = "Jack"; $dog = new Dog(); $dog->name = "Spot"; doSomething($human); doSomething($dog); function doSomething(Mammal $a) { $a->move(); } You can pass Mammals, Dogs and Humans!

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abstract class Mammal { public $name; abstract public function makeSound(); } class Dog extends Mammal { public function makeSound() { print "$this->name is barking\n"; } } class Human extends Mammal { public function makeSound() { print "$this->name is creating älämölö\n"; } } $human = new Human(); $human->name = "Jack"; $dog = new Dog(); $dog->name = "Spot"; doSomething($human); doSomething($dog); function doSomething(Mammal $a) { $a->makeSound(); } Now every Mammal has makeSound method so this will always work!

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interface MovingObject { public function move(); } class Car implements MovingObject { public function move() { print "Car is moving"; } } abstract class Mammal { public $name; abstract public function makeSound(); } class Human extends Mammal implements MovingObject { public function makeSound() { print "$this->name is creating älämölö\n"; } public function move() { print "$this->name is moving"; } } $human = new Human(); $human->name = "Jack"; $car = new Car(); doSomething($human); doSomething($car); function doSomething(MovingObject $a) { $a->move(); } Now you can pass objects that implements MovingObject!

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interface MovingObject { public function move(); } class Car implements MovingObject { public function move() { print "Car is moving"; } } class Robot implements MovingObject { public function move() { print "Robot is moving"; } } class RemoteControl { private $target; public function __construct(MovingObject $target) { $this->target = $target; } public function keyArrowRight() { $this->target->move(); } } $r = new RemoteControl(new Car()); $r->keyArrowRight();