PHP4 vs PHP5 | Difference between PHP4 and PHP5

PHP, Hypertext Preprocessor is a Open Source Language which is trend in the 20th century for creating and developing fast and dynamic web pages.
This is also Server Side Scripting Language with a powerful tool for creating dynamic web pages.
Lets see the difference between PHP version 4 and 5.

Here is the difference between PHP4 and PHP5:

Public, Protected, Private Class Variables

php4: All class variables are public.
php5: Class variables can have differing access levels.

Class Constants

php4: No such thing.
php5: Has them as Class::CONSTANT.

Autoloading

php4: No such thing.
php5: Autoloading exists, provided you write an __autoload function.

Constructors

php4: Constructors are named after their class.
php5: Constructors are named __construct.

Destructors

php4: No such concept.
php5: Destructors are named __destruct.

Interfaces

PHP5 introduces interfaces to help you design common APIs. Interfaces are one type of class where all the methods are abstract. That means all the methods only declared but not defined. All the methods must be defined by its implemented class.

Abstract Classes

PHP5 lets you declare a class as abstract. Abstract classes are the class where one or more methods are abstract but not necessarily all method has to be abstract. Abstract methods are the methods, which are declare in its class but not define. The definition of those methods must be in its extending class.

Exception

PHP5 introduces exceptions handling.

E-Strict Error Level

PHP5 introduces new error level defined as E_STRICT. E_STRICT will notify you when you use depreciated code.

Static Methods and Properties

In PHP5, Static Methods and Properties are also available. When you declare a class as static, then you can access using :: operator without creating an instances of class.