OOP with PHP. Roman Bednarik

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1 Roman Bednarik

2 lecture outline What is PHP Why use OOP with PHP OOP with PHP Advanced topics on OOP and PHP

3 OOP with PHP what is PHP? - development PHP = PHP Hypertext Preprocessor Originally a collection of scripts Developed as open source Major revision in 2001 In 2001 ~ 5 millions of domains using PHP In Oct 2002 ~ 9 millions! Nowadays in version PHP4 (PHP 4.3RC2) this lecture PHP5 in development

4 what is PHP? - usage Server side scripting generating (not only) HTML Strong association with the Apache server and MySQL Many OS covered Great number of additional modules

5 what is PHP? - characteristics Interpreted Loosely type checking Overloading not supported Enables references Case sensitive Variable variable names Associative arrays Serialization of objects into the stream

6 what is PHP? - example PHP source (example.php) <html> <body> <?php Browser view Result of 1+2 =3 Hello world! $A = 1; $B = 2; $C = $A + $B; echo Result of $A+$B=.$C; echo <BR>\n ; echo Hello world! ;?> </body> </html>

7 lecture outline What is PHP Why use OOP with PHP OOP with PHP Advanced topics on OOP and PHP

8 why OOP in PHP Common OOP approach advantages Modularity Less code Reusability Robustness Handling large projects, easy to maintain Classes usually reflect database schema PHP is not inherently OOP language!

9 why OOP in PHP examples Online shops Banking systems News services Editors' systems Home pages => use OOP to separate the functionality from layout

10 lecture outline What is PHP Why use OOP with PHP OOP with PHP (or PHP with OOP?) Advanced topics on OOP and PHP

11 characteristics PHP fulfills: Abstract data types Information hiding Inheritance Polymorphism PHP fails: Later on.. Almost all can be resolved by some of the 'workarounds'

12 <?php OOP with PHP case class class FirstClass { var $x; // data member no ways of specifying private/protected function setx ($a) { $this->x = $a; function getx () { return $this->x; // class function printx(){ echo $this->x; $instancea = new FirstClass;?>

13 Abstract data types Both we have in PHP classes: Data : integer, string, array, associative array, object In PHP: no data protection, public is default Methods: defined as a member functions e.g: function setdata1 ($adata1= default ) { $this -> Data1 = $adata1;

14 Information hiding encapsulation Good practice is to use set and get methods to access the member structures C++, Java, Ada etc. allow protected/private/public PHP only public by default

15 Inheritance In PHP using keyword extends <?php class SecondClass extends FirstClass{ var $Y; function sety ($a) { if ( getx()>0) $this->y = $a; // getx inherited else $this->y = 0;?> Multiple inheritance is not supported

16 Polymorphism All class member functions are virtual by the definition class A { function draw() { echo "1"; // not needed function boo() { $this->draw(); class B extends A { function draw() { echo "drawing B"; $b = new B(); $b->boo(); // outputs drawing B

17 constructors All initialization has to be done in constructor No constructor chaining! => when an object as an instance of derived class is created, only it's constructor is called. If does not exist, parental constructor is called. Solution: Explicit constructor call parent:: name_of_parent_class(); No destructors in PHP automatic garbage collection

18 abstract classes Abstract class is not instantiable No standard way in PHP Solution: Call die in the constructor and methods if the method is not overridden in a derived class the error occurs

19 static variables One instance for all objects of the class No standard way in PHP Workarounds: Global variables: giving a reference of global variable in each constructor call (creation) e.g.:

20 static variables $GLOBALS['_transient']['static']['test']->v1 = 1; // global storage class Test { function Test() { // constructor $this->v1 = & $GLOBALS['_transient']['static']['test']->v1; // link a new variable function printandincrease() { echo "$this->v1 <br>"; $this->v1++; var $v1; $test1 = new Test(); // invokes constructor $test1->printandincrease(); $test2 = new Test(); $test2->printandincrease();

21 PHP fails on No templates No private/protected members No casting from one class to another No static class variables No interfaces No exceptions => many to be resolved in PHP5

22 <?php class Element{ //basic class for all elements function Element($caption=""){ $this->setup($caption); function Setup($caption) { $this->caption = $caption; function Set(){ //virtual methods function Get(){ function GetCaption(){ return $this->caption; function Print_(){?>

23 <?php include_once("class.element.php"); class Button extends Element { //inheritance function Button($caption="",$action=""){ $this->setup($caption,$action); function Setup($caption,$action) { $this->caption = $caption; $this->action = $action; function Print_() { echo "<INPUT TYPE=button "; if ($this->caption) echo "VALUE=\"$this->caption\" "; if ($this->action) echo "OnClick=\"$this->action\" "; echo ">\n";

24 <?php include_once("class.element.php"); include_once("class.button.php"); class Page{ var $reload; function Page($caption="",$obj){ $this->setup($caption,$obj); //add the properties and elements common to all pages $this->reload = new Button("Reload","document.location.reload();"); function Setup($caption, $obj) { $this->caption = $caption; $this->obj = $obj; function GetCaptions() { for ($i=0; $i< count($this->obj); $i++) { echo $this->obj[$i]->getcaption(); echo "<BR>";

25 function print_(){ echo "<HTML>\n <HEAD>\n <TITLE>"; if ($this->caption) echo "$this->caption"; echo " </TITLE>\n"; echo " </HEAD>\n"; echo " <BODY>\n"; $this->reload->print_(); for ($i=0; $i< count($this->obj); $i++) { //invoke Print_() for all //elements on page $this->obj[$i]->print_(); echo "<BR>"; echo " </BODY>\n"; echo "</HTML>\n";?>

26 <?php include("class.element.php");include("class.button.php"); include("class.table.php");include("class.page.php"); $tab= new Table(); $tab->setup("my table 10x3",10,3); $tab2= $tab; $tab2->setup("my table 2 3x3",3,3); $but = new Button("Click me","alert('hello');"); $obs[0] = $tab; $obs[1] = $tab2; $obs[2] = $but; $page= new Page("Object Page",$obs); $page->print_(); $page->getcaptions();?>

27 lecture outline What is PHP Why use OOP with PHP OOP with PHP Advanced topics on OOP and PHP

28 Generic function for setting the member variables function Set ($varname, $value) { $this->$varname = $value; $instance->set ('size','5');

29 Serializing the objects Partially overcomes the need for a persistent object!!saves only data members, not methods! (PHP4 is exception) <?php $mycart = new ShoppingCart(); $stream1 = serialize($mycart); // and store to file or db // retreive from file/db after a year.. $mylatercart = unserialize($stream1);?> Not recommended to use!

30 Overloading in PHP <?php class ShoppingCart{ function ShoppingCart(){ $to_call="shoppingcart".func_num_args(); $args = func_get_args(); // return an array of arguments $args = implode(':',$args); $args = str_replace( :,,, $args); $run = \$this->$to_call ($args); ; // variable variable eval ($run); function ShoppingCart1($x= 2 ) { code1(); function ShoppingCart2($x= 2,$y= 3 ) { code2();?>

31 Serializing the objects (cont.) Stream is a string with defined format One might try to investigate it: $mycart = new ShoppingCart(); $stream1 = serialize($mycart); $hocus = explode(':',$stream1); // split $stream1 by : into array e.g. $classname = str_replace( \, '',$hocus[2] ); // takes away the

33 USE OOP! Thank you

CS 6456 OBJCET ORIENTED PROGRAMMING IV SEMESTER/EEE

CS 6456 OBJCET ORIENTED PROGRAMMING IV SEMESTER/EEE PART A UNIT I 1. Differentiate object oriented programming from procedure oriented programming. 2. Define abstraction and encapsulation. 3. Differentiate