Custom exception classes in PHP - Mini Project: Build & Apply

Custom Exception Classes in PHP

📖 Scenario: Imagine you are building a simple banking system. You want to handle errors like withdrawing too much money or depositing invalid amounts in a clear way.

🎯 Goal: You will create custom exception classes to handle specific banking errors and use them in your code to show meaningful error messages.

📋 What You'll Learn

Create a custom exception class called InsufficientFundsException

Create a custom exception class called InvalidDepositException

Write a function withdraw that throws InsufficientFundsException if withdrawal amount is more than balance

Write a function deposit that throws InvalidDepositException if deposit amount is less than or equal to zero

Use try and catch blocks to handle these exceptions and print error messages

💡 Why This Matters

🌍 Real World

Custom exceptions help you handle specific errors in your programs clearly, like banking errors or user input mistakes.

💼 Career

Understanding custom exceptions is important for writing robust, maintainable code in professional software development.

1

Create the initial balance variable

Create a variable called $balance and set it to 1000.

PHP

<?php

// Create a variable called $balance and set it to 1000
// Your code here

Need a hint?

Use $balance = 1000; to set the starting balance.

2

Create custom exception classes

Create two custom exception classes called InsufficientFundsException and InvalidDepositException that both extend the built-in Exception class.

PHP

<?php

$balance = 1000;

// Create class InsufficientFundsException that extends Exception
// Create class InvalidDepositException that extends Exception
// Your code here

Need a hint?

Use class ClassName extends Exception {} to create custom exceptions.

3

Write withdraw and deposit functions with exceptions

Write a function called withdraw that takes $amount and throws InsufficientFundsException if $amount is greater than $balance. Write a function called deposit that takes $amount and throws InvalidDepositException if $amount is less than or equal to zero. Both functions should update the global $balance variable accordingly.

PHP

 balance
// Write function deposit that throws InvalidDepositException if amount <= 0
// Your code here

Need a hint?

Use throw new ExceptionName("message") inside the functions to raise errors.

4

Use try-catch blocks to handle exceptions and print results

Use try and catch blocks to call withdraw(1500) and deposit(-100). Catch InsufficientFundsException and InvalidDepositException separately and print their messages. Then print the final $balance.

PHP

 $balance) {
        throw new InsufficientFundsException("Cannot withdraw $amount: insufficient funds.");
    }
    $balance -= $amount;
}

function deposit($amount) {
    global $balance;
    if ($amount <= 0) {
        throw new InvalidDepositException("Cannot deposit $amount: invalid amount.");
    }
    $balance += $amount;
}

// Use try-catch to call withdraw(1500) and deposit(-100)
// Catch exceptions and print messages
// Print final balance
// Your code here

Need a hint?

Use separate try blocks for each function call and catch the specific exceptions to print their messages.