The difference between PHP4 and PHP5

The objects in the PHP5 have been systematically and comprehensively tuned, and may now look somewhat similar to Java. This section focuses on the new object patterns in PHP5, with some simpler examples to illustrate. Let this section be a new starting point for your PHP5 journey. ：）

* Constructors and destructors

* References to Objects

* Cloning of objects

* Private, public, and protected mode in the object

* Interface (interfaces)

* Abstract class

* __call

* __set and __get

* Static member

Constructors and destructors

In PHP4, when a function has the same name as an object, the function becomes the constructor of the object, and there is no concept of destructors in the PHP4.

In PHP5, constructors are uniformly named __construct, and the concept of destructors is introduced, which is uniformly named __destruct.

Example one: constructors and destructors

class Foo {

var $x;

function __construct ($x) {

$this->x = $x;

}

function display () {

Print ($this->x);

}

function __destruct () {

Print ("Bye Bye");

}

}

$o 1 = new Foo (4);

$o 1->display ();

?>

In the above example, when you terminate the call to the Foo class, its destructor will be invoked, and the "Bye Bye" will be printed in the example above.

References to Objects

As we all know, in the PHP4, passing a variable to a function or method, which actually makes a copy of the variable, means that you pass a copy of the variable to the function or method, unless you use the reference symbol "&" to declare a reference, not a copy. In PHP5, an object is always in the form of a reference, and the assignment operation in the object is also a reference operation.

Example two: A reference to an object

class Foo {

var $x;

function SetX ($x) {

$this->x = $x;

}

function GetX () {

return $this->x;

}

}

$o 1 = new Foo;

$o 1->setx (4);

$o 2 = $o 1;

$o 1->setx (5);

if ($o 1->getx () = = $o 2->getx ()) print ("Oh my god!");

?>

Cloning of objects

What if I want to get a copy of an object that is always invoked as a reference, as described above? PHP5 provides a new feature, that is, the cloning of objects, the syntax is __clone.

Example three: Cloning of objects

class Foo {

var $x;

function SetX ($x) {

$this->x = $x;

}

function GetX () {

return $this->x;

}

}

$o 1 = new Foo;

$o 1->setx (4);

$o 2 = $o 1->__clone ();

$o 1->setx (5); if ($o 1->getx ()!= $o 2->getx ()) print ("Copies are independant");

?>

The method of object cloning exists in many other application languages, so you don't have to worry about its stability. ：）

Private, public, and protected mode in the object

In PHP4, all the methods and variables of an object are public, which means that you can manipulate any one of these variables and methods outside of an object. PHP5 introduced three new patterns for controlling this access, which are public, protected (Protected), and proprietary (private).

Common mode (public): Allows manipulation control outside the object.

Private mode: Only the methods within this object are allowed to manipulate it.

Protected Mode (Protected): Allows this object and its parent object to manipulate it.