Custom exception classes in PHP - Step-by-Step Execution

Concept Flow - Custom exception classes

Start

↓

Define custom exception class

↓

Try block: code runs

↓

Exception thrown?

No→Continue normal flow

Yes↓

Catch block: catch custom exception

↓

Handle exception

↓

End

This flow shows how a custom exception class is defined, then used in a try block, caught, and handled.

Execution Sample

PHP

<?php
class MyException extends Exception {}

try {
  throw new MyException("Oops!");
} catch (MyException $e) {
  echo $e->getMessage();
}

This code defines a custom exception, throws it, catches it, and prints its message.

Execution Table

Step	Action	Evaluation	Result
1	Define class MyException extending Exception	Class created	MyException ready
2	Enter try block	No exception yet	Running code inside try
3	Throw new MyException with message 'Oops!'	Exception thrown	MyException object created
4	Catch block matches MyException	Catch block entered	Exception caught
5	Call getMessage() on exception	Returns 'Oops!'	Output: Oops!
6	End of script	No more code	Script ends

💡 Exception thrown and caught, script ends normally

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
$e	undefined	MyException object with message 'Oops!'	Same object in catch	Same object

Key Moments - 3 Insights

Why do we extend Exception to create a custom exception?

Extending Exception lets us create a new type of error that can be caught separately, as shown in step 1 and step 4 of the execution_table.

What happens if we throw an exception but don't catch it?

If not caught, the script stops with an error. Here, step 4 shows catching prevents that and allows handling.

How do we get the message from the exception?

We call getMessage() on the exception object, as shown in step 5 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output at step 5?

A Oops!

B MyException

C No output

D Error message

💡 Hint

Check the 'Result' column at step 5 in execution_table

At which step does the exception get caught?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look for 'Catch block entered' in the 'Evaluation' column

If we remove the catch block, what happens to the script?

A It runs normally without output

B It throws an uncaught exception error

C It prints 'Oops!' automatically

D It ignores the exception

💡 Hint

Refer to key_moments about what happens if exception is not caught

Concept Snapshot

Custom exception classes in PHP:
- Define by extending Exception class
- Use try block to run code
- Throw custom exception with throw
- Catch with catch (CustomException $e)
- Access message with getMessage()

Full Transcript

This example shows how to create a custom exception class in PHP by extending the built-in Exception class. The code runs inside a try block where it throws the custom exception. The catch block catches this specific exception type and handles it by printing the message. The execution table traces each step: defining the class, entering try, throwing exception, catching it, printing message, and ending the script. Variables track the exception object as it is created and caught. Key moments clarify why extending Exception is needed, what happens if exceptions are not caught, and how to get the message. The quiz tests understanding of output, catching step, and behavior without catch. The snapshot summarizes the syntax and flow for quick reference.