What are Exceptions?

[MUSIC] 0:00 Hi, I'm Alena. 0:05 Exceptions are the object oriented approach to handling errors. 0:07 An exception is an object that's thrown by your application 0:10 in the event that something goes wrong. 0:14 This allows you to interrupt the flow of the program and customize 0:16 how the application handles errors, or gracefully exit the application. 0:20 When an exception is thrown it halts 0:26 the processing until the exception is either caught or left on handled. 0:28 If left on handled the exception stops the application. 0:33 This unhandled exception is the typical behavior for a fatal error. 0:37 But what makes exceptions, exceptionally useful is the ability to catch them. 0:40 Catching exceptions allows us to recover gracefully and 0:46 either exit our application or customize the error. 0:50 We can customize what happens based on what type of exception we receive. 0:54 I can put the yellow balls in a bag, the blue ball in a basket, 1:00 and the red ball in a box to mail somewhere else. 1:05 In production, unhandled exceptions who cause the page to stop loading, or 1:11 not load it all, but catching exceptions gives you the ability 1:16 to determine what happens with each exception. 1:20 You might redirect a user to an error page, log an issue, or 1:23 do any other type of error handling. 1:27 Let's take a look at the syntax used for 1:30 catching database exceptions with the PHP data object. 1:32 First, we have the keyword, try, 1:37 then within curly braces we have the code we want to try, or 1:39 attempt to execute, in this case, connecting to a sqlite database. 1:43 If there is an error in the connection, such as spelling sqlite with two Ls, 1:49 the PTO class will throw an exception that we catch in the next block. 1:54 After the keyword, catch, we use parenthesis to tell PHP what 1:59 we'll be catching, in this case, exception. 2:03 We then assign the exception that was caught to a new variable, e. 2:07 Then we can use that exception variable to get details using the exception methods. 2:13 We've used three methods for 2:18 this message, get message, returns, could not find driver. 2:19 Get file, returns the full path to the file. 2:25 And get line, returns the line number where the exception occurred. 2:29 You wouldn't want all these details displayed in production. 2:34 You would probably show a simple error message and log more details. 2:36 You could also try a secondary database connection at this point. 2:41 What happens in the catch block is really up to you and 2:46 the requirements of your application. 2:49 There are additional methods available for the exception class, so 2:50 make sure you check the notes associated with this video for more details. 2:55 In the next few videos we'll cover more details on how to use exceptions and 3:00 under what conditions. 3:05 But, first, here are four tips for making proper use of exceptions. 3:07 First, exceptions are part of object oriented programming. 3:12 Since an exception is an object itself, 3:16 it's really designed to work best with an object oriented approach to programming. 3:19 PHP offers a number of options for 3:25 error handling when working with procedural code. 3:27 In most cases, I recommend using errors for procedural code and 3:30 exceptions when working with objects. 3:34 If you haven't seen the workshop on error handling, 3:37 check the notes attach this video for more details. 3:40 Second, exceptions are exceptional. 3:44 Don't use exceptions to manage normal program flow. 3:48 A try catch block is not an if else statement, 3:52 your application should still function without the try catch block. 3:56 Third, exceptions are meant to be handled. 4:01 The very existence of a try catch block 4:04 indicates that exceptions are meant to be handled. 4:07 They are meant to be resolved, even if that resolution 4:10 is to rethrow the exception after doing some sort of error handling. 4:14 With errors, fatal or 4:18 otherwise, there's the possibility that something was completed halfway. 4:20 Exceptions help eliminate this possibility by halting processing long enough for 4:25 you to clean up before terminating the application. 4:30 For example, closing the connection to a database, or 4:34 cleaning up half written file. 4:37 And finally, exceptions are not meant to be silenced. 4:40 If you have an empty catch block, you are silencing the exception. 4:44 The application will not be halted and 4:48 there is no error handling in the catch block. 4:51 The exception simply disappears. 4:53 PHP throws exceptions because there's a problem, and frameworks do the same. 4:57 Handle those exceptions, don't just silence them. 5:02 Quietly handling exceptions is not the same as silencing them. 5:06 If an exception is thrown because a file does not exist, and 5:10 in your catch block you create that file, 5:14 the exception has now been handled and your code may continue processing. 5:17 Exceptions are thrown for a reason. 5:23 Catch them, handle them, don't ignore or silence them. 5:24