phpapprentice/code/exceptions.php

<?php

// Sometimes things go wrong when someone uses your code. How do we handle this situation?
// PHP has Exceptions to define errors and the ability to "throw" them to stop code
// execution and tell the user of your code that something is wrong.
class Processor
{
    public function charge($creditCard)
    {
        if (strlen($creditCard->getNumber()) !== 16) {
            throw new Exception('Credit card is not right');
        }
    }
}

// In this case, if someone tried to use the Processor class
// to charge a credit card number that is not 16 characters long, an
// exception will be thrown which stops the rest of the code from running.
$processor = new Processor();
$processor->charge('1234');

// A developer who wants to prevent an exception from stopping code execution
// can catch the exception and use it for logging or display the error to a user.

// Just wrap the code that might throw an exception with the keyword "try" and brackets
// followed by "catch", the exception type in parentheses and more brackets.
try {
    $processor->charge('1234');
} catch (Exception $e) {
    echo $e->getMessage() . "\n";
}

// You can make your own custom exceptions as well. They are just classes
// that extend Exception.
class MyCustomException extends Exception {}

// Then, you can try to catch your exception instead of the base exception.
try {
    throw new MyCustomException('I am a custom exception');
} catch (MyCustomException $e) {
    echo "Cauth MyCustomException\n";
}

// Since all exceptions inherit from Exception, catching
// Exception will catch any and all exceptions that might be thrown.
try {
    throw new MyCustomException('I inherit from Exception');
} catch (Exception $e) {
    echo "Still caught MyCustomException\n";
}

// You can also create multiple catch blocks to handle different types of exceptions in
// one try-catch.
try {
    throw new MyCustomException('I am being thrown again');
} catch (MyCustomException $e) {
    echo "MyCustomException was caught\n";
} catch (Exception $e) {
    echo "Just in case a different exception is thrown\n";
}