ZEND PHP 5 Certification STUDY GUIDE

128 ” Object Oriented Programming in PHP
Determining An Object’s Class
It is often convenient to be able to determine whether a given object is an instance
of a particular class, or whether it implements a specific interface. This can be done
by using the instanceof operator:
if ($obj instanceof MyClass) {
echo "\$obj is an instance of MyClass";
}
Naturally, instanceof allows you to inspect all of the ancestor classes of your object,
as well as any interfaces.
Exceptions
Even though they have been a staple of object-oriented programming for years, exceptions
have only recently become part of the PHP arsenal. Exceptions provide an
error control mechanism that is more fine-grained than traditional PHP fault handling,
and that allows for a much greater degree of control.
There are several key differences between “regular” PHP errors and exceptions:
• Exceptions are objects, created (or “thrown”) when an error occurs
• Exceptions can be handled at different points in a script’s execution, and different
types of exceptions can be handled by separate portions of a script’s
code
• All unhandled exceptions are fatal
• Exceptions can be thrown from the __construct method on failure
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• Exceptions change the flow of the application
The Basic Exception Class
As we mentioned in the previous paragraph, exceptions are objects that must be
direct or indirect (for example through inheritance) instances of the Exception base
class. The latter is built into PHP itself, and is declared as follows: