The support for creating objects was from era of PHP3 but there was only the limited support of OOPS. Originally OOPS support was only meant to provide grouping of both data and functions together. As the PHP popularity grew the OOPS need also grew.
There were many significant changes in PHP5. Earlier was a very little support of encapsulation, and was only limited to grouping of data and functions or I can say that all the implementation was visible outside the class. But in PHP5 the concept of private and protected member variables and methods was introduced. Now the data protection is also possible with PHP5. The public, private and protected provide the various access levels.
PHP5 provide support for the constructors and destructors via member functions __construct and __destruct(). Constructors are the member functions that are automatically called when the instance of class in created. The earlier version of PHP the constructors were with the same name as of the class name. This unified constructor scheme helps in encapsulation of overridden subclass constructors. PHP 5 introduces a destructor support similar to that of other object-oriented languages, such as C++. The destructor method will be called as soon as all references to a particular object are removed or when the object is explicitly destroyed.
In PHP5 provides the concept of abstract classes and interfaces. For an abstract class we cannot create an instance of a class. Only non-abstract classes can be instantiated. For a methods defined abstract, only the method's signature can be defined not their implementation. Interface allows you to define certain methods, which a class must implement. In interface we provide only the signature of member functions but the definitions are provided in the class that implements interface. The class that provides the implementation of an interface must define all the methods of interface otherwise the error will rise.
Like other programming languages there is also the support for final and static keywords in PHP5.The final keyword does not allow class and the member functions to be further extended. The classes declared with final keyword cannot further extended. The member or method declared with static keyword can't be accessed by the instance of object. Since static methods are callable without an instance of the object created, so $this is not available inside the method declared as static.
PHP5 has better error handling support. It provides exception model similar to that of other programming languages like java or C#. An exception can be thrown and caught. Code is surrounded by try block, to catch various exceptions. Each try must have at least one corresponding catch block. Normal execution (when no exception is thrown within the try block, or catch the matching exception thrown.