问为什么我要在php中使用异常处理？

EN

class Application
{
    public function run()
    {
        try {
            // Start her up!!
        } catch (Exception $e) {
            // If Ajax request, send back status and message
            if ($this->getRequest()->isAjax()) {
                return Application_Json::encode(array(
                    'status' => 'error',
                    'msg'    => $e->getMessage());
            }

            // ...otherwise, just throw error
            throw $e;
        }
    }
}

class StringsOnly
{
    public function onlyPassStringToThisMethod($string)
    {
        if (!is_string($string)) {
            throw new InvalidArgumentException('$string is definitely not a string');
        }

        // Cool string manipulation...

        return $this;
    }
}

class DifferentExceptionsForDifferentFolks
{
    public function catchMeIfYouCan()
    {
        try {
            $this->flyForFree();
        } catch (CantFlyForFreeException $e) {
            $this->alertAuthorities();
            return 'Sorry, you can\'t fly for free dude. It just don\'t work that way!';
        } catch (DbException $e) {
            // Get DB debug info
            $this->logDbDebugInfo();
            return 'Could not access database. What did you mess up this time?';
        } catch (Exception $e) {
            $this->logMiscException($e);
            return 'I catch all exceptions for which you did not account!';
        }
    }
}

class CreditCardController extends Zend_Controller_Action
{
    public function buyforgirlfriendAction()
    {
        try {
            $this->getDb()->beginTransaction();

            $this->insertGift($giftName, $giftPrice, $giftWowFactor);

            $this->getDb()->commit();
        } catch (Exception $e) {
            // Error encountered, rollback changes
            $this->getDb()->rollBack();

            // Re-throw exception, allow ErrorController forward
            throw $e;
        }
    }
}