Object-Oriented Programming

Members

• Members are public by default
• The declaration for a data member has to be preceded by at least one keyword

<?php
class MyClass {
    public $str1 = 'This is a member';
    const str2   = 'This is a constant';
    static $str3 = 'This is a static member';
}

$obj = new MyClass();

echo $obj->str1     . "\n";   # member
echo MyClass::str2  . "\n";   # constant
echo MyClass::$str3 . "\n";   # static member
?>

Methods

• Methods are public by default

<?php
class MyClass {
    function foo1() {
        echo "foo1\n";
    }
    static function foo2() {
        echo "foo2\n";
    }
}

$obj = new MyClass();

$obj->foo1();      # method
MyClass::foo2();   # static method
?>

Constructors

• If a constructor is defined for a child class, the parent constructor will only be run if it is explicitly called: parent::__construct()
  

<?php
class MyClass {
    function __construct($str) {
        echo "$str\n";
    }
}

$obj = new MyClass('hello');
?>

PHP5

Features supported

• Private, public and protected methods and variables
• Static methods and variables (class methods and variables) (static keyword)
• Constant class variables (const keyword) (static keyword is not needed)

• Interfaces (interface and implements keywords)
• Abstract classes and methods (abstract keyword)
• Final classes, methods, and variables (final keyword) (cannot be overridden by a child class)

• Objects as references (objects are always assigned, passed, and returned by reference)
• Cloning objects (__clone method)
• Constructors and destructors (__construct, __destruct) (can optionally still use the name of the class as the name of the constructor)

• Exceptions (throw, try, catch) (Extending the Exception base class involves creating a constructor and a getMessage method)
• Type hinting (indicate the expected type of a method parameter) (function process_foo_class(foo_class $foo))

• __call (optional default method for a class) (can be used to indirectly overload functions) (function __call($name,$arguments))
• __set (optional default method for accessing undefined variables) (function __set($name,$val))
• __get (optional default method for setting undefined variables) (function __get($name))

Features not supported

• Multiple inheritance
• Exceptions (catch all and finally)

PHP4

• PHP4 is not an OO language, though it provides some OO features.
• The OO mechanisms are slow and limited.
• It's best to avoid using OOP in PHP4, unless speed is not at a factor.

Features not supported

• Static variables (class variables)
• Protected and private member variables
• Object references (have to put the object in a variable, and then use a reference to this variable)