Built in Classes

Every OOP language comes with some built-in classes, and PHP is no exception. PHP 5 introduces the Standard PHP Library (SPL), which provides a number of ready-made classes and interfaces. As of version 5.1, depending upon how PHP is configured, all in all, there are well over 100 built-in classes and interfaces-a healthy increase from the number available in version 5.0.

Having ready-made objects speeds up development, and native classes written in C offer significant performance advantages. Even if these built-in classes do not do exactly what you want, they can easily be extended to suit your needs.

Exceptions

All OOP languages support exceptions, which are the OO way of handling errors. In order to use exceptions, we need the keywords try, catch, and throw. A try block encloses code that may cause an error. If an error occurs, it is thrown and caught by a catch block. The advantage of exceptions over errors is that exceptions can be handled centrally, making for much cleaner code. Exceptions also significantly reduce the amount of error-trapping code you need to write, which offers welcome relief from an uninspiring task. Also, having a built-in exception class makes it very easy to create your own customized exceptions through inheritance.

Database Classes

Because PHP is all about building dynamic web pages, database support is allimportant. PHP 5 introduces the mysqli (MySQL Improved) extension with support for the features of MySQL databases versions 4.1 and higher. You can now use features such as prepared statements with MySQL, and you can do so using the built-in OO interface. In fact, anything you can do procedurally can also be done with this interface.

SQLite is a database engine that is incorporated directly into PHP. It is not a general-purpose database like MySQL, but it is an ideal solution in some situations, in many cases producing faster, leaner, and more versatile applications. Again an entirely OO interface is provided.

PHP versions 5.1 and higher also bundle PHP Data Objects (PDO) with the main PHP distribution. If you need to communicate with several different database back ends, then this package is the ideal solution. PDO’s common interface for different database systems is only made possible by the new object model.

Web Services

In PHP 5 all Extensible Markup Language (XML) support is provided by the libxml2 XML toolkit (www.xmlsoft.org). The underlying code for the Simple API for XML (SAX) and for the Document Object Model (DOM) has been rewritten, and DOM support has been brought in line with the standard defined by the World Wide Web Consortium.

Unified treatment of XML under libxml2 makes for a more efficient and easily maintained implementation. This is particularly important because support for XML under PHP 4 is weak, and web services present many problems that require an OO approach.

Under PHP 4, creating a SOAP client and reading an RSS feed are challenging programming tasks that require creating your own classes or making use of external classes such as NuSOAP (http://sourceforge.net/ projects/nusoap). There is no such need in PHP 5.

Reflection Classes

The reflection classes included in PHP 5 provide ways to introspect objects and reverse engineer code. The average web developer might be tempted to ignore these classes.

Iterator

In addition to built-in classes, PHP 5 also offers built-in interfaces. Iterator is the most important, as a number of classes and interfaces are derived from this interface.