Summary - Error handling

PHP course · Intermediate · Lesson 104/115

Build an age-checking function with try/catch, throw and custom exceptions.

Summary - Error handling

In this group you learned the five pillars of exception handling: catching with try/catch, throwing with throw, the Exception methods, choosing levels with error_reporting and writing custom exception classes.

Combined, they form a robust age check: you define a custom exception, throw it when a condition fails, catch it with try/catch and show a meaningful message to the user.

The last step is a mini app that puts the whole flow together.

Combine the age check

An age check has three parts: define (a custom exception), throw (when the condition fails) and catch (with try/catch).

First write InvalidAgeException extends Exception. Then, inside the verifyAge(int $age) function, if age is under 18, call throw new InvalidAgeException(...).

Finally call try { verifyAge(15); } and print the message with catch (InvalidAgeException $e).

Exercise Summary - Age check mini app

Define the InvalidAgeException class with extends Exception. Write a verifyAge(int $age): void function: if age is under 18, throw new InvalidAgeException("Too young"). Call verifyAge(15) inside try/catch, catch the error and print its message.

Show example solution

void; if ($age < 18) throw new InvalidAgeException("Too young"). Then try { verifyAge(15); } catch (InvalidAgeException $e) { echo $e->getMessage() . "\n"; }.
Example solution:
<?php
// Define InvalidAgeException and verifyAge
class InvalidAgeException extends Exception {
}

function verifyAge(int $age): void {
    if ($age < 18) {
        throw new InvalidAgeException("Too young");
    }
    echo "Welcome\n";
}

try {
    verifyAge(15);
} catch (InvalidAgeException $e) {
    echo $e->getMessage() . "\n";
}

Test yourself

Match the five pillars

try/catch

Catches the exception
throw

Throws the exception
getMessage()

Reads the message
error_reporting

Selects the levels
extends Exception

Derives a custom class

Throw in the age check

<?php
function verifyAge(int $age): array {
    if ($age < 18) {
        ____ new InvalidAgeException("Too young");
    }
    return ['ok' => true];
}

Show answer

<?php
function verifyAge(int $age): array {
    if ($age < 18) {
        throw new InvalidAgeException("Too young");
    }
    return ['ok' => true];
}

Summary - Error handling