Web Database Applications with PHP, and MySQL

Objects

PHP has limited support for object-oriented programming and allows programmers to define their own classes and create object instances of those classes. We make little use of objects in this book, and this section serves as an introduction to PHP’s support of object-oriented features. The subject of object-oriented programming is extensive, and we don’t provide a complete explanation of the subject here.

Classes and Objects

A class defines a compound data structure made up of member variables and a set of functions—known as methods or member functions—that operate with the specific structure. Example 2-7 shows how a class Counter is defined in PHP. The class Counter contains two member variables—the integers $count and $startPoint—and four functions that use these member variables. Collectively, the variables and the functions are members of the class Counter.

Example 2-7. A simple class definition of the user-defined class Counter

<?php
  // A class that defines a counter.
  class Counter
  {
    // Member Variables
    var $count = 0;
    var $startPoint = 0;

    // Methods
    function startCountAt($i)
    {
      $this->count = $i;
      $this->startPoint = $i;
    }    
  
    function increment(  )
    {
      $this->count++;
    }
    
    function reset(  )
    {
      $this->count = $this->startPoint;
    }

    function showvalue(  )
    {
      print $this->count;
    }
  }
?>

To use the data structures and functions defined in a class, an instance of the class—an object—needs to be created. Like other data types—integers, strings, arrays, and so on—objects are held by variables. ...