CHAPTER 1 ■ OBJECT ORIENTATION
7
// be created.
function __construct($ename, $sal = 100) {
$this->ename = $ename;
$this->sal = $sal;
}
function give_raise($amount) {
$this->sal+= $amount;
printf("Employee %s got raise of %d dollars\n", $this->ename, $amount);
printf("New salary is %d dollars\n", $this->sal);
}
function __destruct() {
printf("Good bye, cruel world: EMPLOYEE:%s\n", $this->ename);
}
} // End of class "employee"
class manager extends employee {
protected $dept;
function __construct($ename, $sal, $dept) {
parent::__construct($ename, $sal);
$this->dept = $dept;
}
function give_raise($amount) {
parent::give_raise($amount);
print "This employee is a manager\n";
}
function __destruct() {
printf("Good bye, cruel world: MANAGER:%s\n", $this->ename);
parent::__destruct();
}
} // End of class "manager"
This code is completely equivalent to the original script1.2.php in Listing 1-2, except it is much
easier to read, because the most important part is contained in the file script1.3.php in Listing 1-3. The
other file, ACMEmanager.php, only contains the class declarations. If we’re not really interested in the
internals of the class declarations, we don’t have to read them; we only have to know how the objects of
the declared classes behave. Also, note that the file is named after the first class that is being
instantiated. When that file is loaded, the class employee will also be defined, because the definition of
both classes is in the same file.
The second thing to note is that the class name was prefixed by “ACME.” This is to alert the reader of
the possibility of creating specialized, per-project class libraries. The function __autoload implemented
here uses require_once instead of an include directive. The reason for that is the behavior of PHP, which
will terminate the script if a file requested by the require directive is not available. The execution will
proceed if the file simply included by an include directive is not available. Executing a script that
depends on class definitions without those definitions being available doesn’t make much sense.
Also, class definition files should not have a trailing ?> defined. This is because they can often be
autoloaded or included in a “header” file before the page is assembled, and any extra white space
between the ?> and EOF will be injected into the html output stream of the page at the start. PHP is quite
happy not to have the trailing ?>, omitting it is a best practice. This is probably the single biggest cause of
“output already started” errors when using the header() function to send HTTP headers back to the
browser, and for the unaware it is a death trap.
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