ZEND PHP 5 Certification STUDY GUIDE

132 ” Object Oriented Programming in PHP
}
echo $e->getMessage();
set_exception_handler("handleUncaughtException");
throw new Exception("You caught me!");
echo "This is never displayed";
i
Note that, because the catch-all exception handler is only called after the exception
has bubbled up through the entire script, it, just like an all-encompassing try...
catch block, is the end of the line for your code—in other words, the exception has
already caused a fatal error, and you are just given the opportunity to handle it, but
not to recover from it. For example, the code above will never output You caught me!,
because the exception thrown will bubble up and cause handleUncaughtException()
to be executed; the script will then terminate.
If you wish to restore the previously used exception handler, be it the default of a fatal
error or another user defined callback, you can use restore_exception_handler().
Lazy Loading
Prior to PHP 5, instantiating an undefined class, or using one of its methods in a
static way would cause a fatal error. This meant that you needed to include all of the
class files that you might need, rather than loading them as they were needed—just
so that you wouldn’t forget one—or come up with complicated file inclusion mechanisms
to reduce the needless processing of external files.
To solve this problem, PHP 5 features an “autoload” facility that makes it possible
to implement “lazy loading”, or loading of classes on-demand. When referencing
a non-existent class, be it as a type hint, static call, or attempt at instantiating an
object, PHP will try to call the __autoload() global function so that the script may be
given an opportunity to load it. If, after the call to autoload(), the class is still not
defined, the interpreter gives up and throws a fatal error.
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