Custom exception classes in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of custom exception message

What is the output of this PHP code when the exception is thrown and caught?

PHP

<?php
class MyException extends Exception {}

try {
    throw new MyException("Error happened");
} catch (MyException $e) {
    echo $e->getMessage();
}
?>

A No output

B Fatal error

C Error happened

D Exception

💡 Hint

Look at how the exception message is accessed inside the catch block.

The custom exception inherits from Exception and the message passed is 'Error happened'. The catch block prints the message using getMessage(), so the output is exactly that string.

❓ Predict Output

intermediate

Custom exception with additional property

What will be the output of this PHP code?

PHP

<?php
class MyException extends Exception {
    private $codeNumber;
    public function __construct($message, $codeNumber) {
        parent::__construct($message);
        $this->codeNumber = $codeNumber;
    }
    public function getCodeNumber() {
        return $this->codeNumber;
    }
}

try {
    throw new MyException("Error", 404);
} catch (MyException $e) {
    echo $e->getMessage() . ' ' . $e->getCodeNumber();
}
?>

A Error 404

B Error 0

C Error

D Fatal error: Uncaught Error

💡 Hint

Check how the custom property is set and accessed.

The constructor sets the message and the custom codeNumber property. The catch block prints both the message and the codeNumber, so output is 'Error 404'.

❓ Predict Output

advanced

Exception inheritance and catch order

What will be the output of this PHP code?

PHP

<?php
class BaseException extends Exception {}
class ChildException extends BaseException {}

try {
    throw new ChildException("Child error");
} catch (BaseException $e) {
    echo "Caught BaseException: " . $e->getMessage();
} catch (ChildException $e) {
    echo "Caught ChildException: " . $e->getMessage();
}
?>

A No output

B Caught ChildException: Child error

C Fatal error: Uncaught ChildException

D Caught BaseException: Child error

💡 Hint

Remember catch blocks are checked in order and ChildException is a subclass of BaseException.

The first catch block matches because ChildException is a subclass of BaseException. So it catches the exception and prints the message with 'Caught BaseException:'. The second catch block is never reached.

❓ Predict Output

advanced

Custom exception with overridden __toString method

What is the output of this PHP code?

PHP

<?php
class MyException extends Exception {
    public function __toString() {
        return "MyException: " . $this->getMessage();
    }
}

try {
    throw new MyException("Something went wrong");
} catch (MyException $e) {
    echo $e;
}
?>

A MyException: Something went wrong

B Something went wrong

C Fatal error: Object of class MyException could not be converted to string

D Exception: Something went wrong

💡 Hint

Check how the __toString method affects printing the exception object.

The __toString method is overridden to return 'MyException: ' plus the message. When echoing the exception object, this method is called, so the output is 'MyException: Something went wrong'.

🧠 Conceptual

expert

Behavior of uncaught custom exceptions

What happens if a custom exception thrown in PHP is not caught anywhere in the code?

A The exception is ignored and the script continues running normally.

B The script stops and a fatal error message with the exception details is displayed.

C The exception is automatically caught by a default handler and logged silently without stopping the script.

D The exception causes a warning but the script continues execution.

💡 Hint

Think about what happens when an exception is not handled in PHP.

In PHP, if an exception is thrown and not caught, the script stops execution and a fatal error message is shown with the exception details. This helps to avoid silent failures.

Practice

1.

What is the main purpose of creating a custom exception class in PHP?

easy

A. To define specific error types for clearer error handling

B. To replace the built-in Exception class completely

C. To speed up the execution of the program

D. To automatically fix errors in the code

Solution

1. Step 1: Understand the role of custom exceptions

   Custom exceptions allow programmers to create specific error types that represent particular problems in the code.

2. Step 2: Compare with other options

   Custom exceptions do not replace the built-in Exception class, nor do they speed up execution or fix errors automatically.

3. Final Answer:

   To define specific error types for clearer error handling -> Option A

4. Quick Check:

   Custom exceptions = Specific error types [OK]

Hint: Custom exceptions clarify errors by type, not fix or speed [OK]

Common Mistakes:

• Thinking custom exceptions replace built-in Exception
• Believing custom exceptions fix errors automatically
• Assuming custom exceptions improve performance

2.

Which of the following is the correct way to declare a custom exception class named MyError in PHP?

?

easy

A. class MyError extends Error {}

B. class MyError implements Exception {}

C. class MyError extends Exception {}

D. class MyError inherits Exception {}

Solution

1. Step 1: Recall PHP syntax for custom exceptions

   Custom exceptions extend the built-in Exception class using the keyword extends.

2. Step 2: Check each option

   class MyError extends Exception {} correctly uses extends Exception. class MyError implements Exception {} wrongly uses implements, which is for interfaces. class MyError extends Error {} extends Error, which is a different base class. class MyError inherits Exception {} uses invalid syntax inherits.

3. Final Answer:

   class MyError extends Exception {} -> Option C

4. Quick Check:

   Custom exception syntax = extends Exception [OK]

Hint: Use 'extends Exception' to create custom exceptions [OK]

Common Mistakes:

• Using 'implements' instead of 'extends'
• Using 'inherits' keyword which is invalid
• Extending Error instead of Exception

3.

What will be the output of the following PHP code?

class MyException extends Exception {}

try {
    throw new MyException("Custom error happened");
} catch (MyException $e) {
    echo $e->getMessage();
} catch (Exception $e) {
    echo "General error";
}

medium

A. Custom error happened

B. General error

C. Fatal error: Uncaught exception

D. No output

Solution

1. Step 1: Understand the thrown exception type

   The code throws an exception of type MyException.

2. Step 2: Check catch blocks order and matching

   The first catch block matches MyException, so it catches the exception and echoes the message.

3. Final Answer:

   Custom error happened -> Option A

4. Quick Check:

   Matching catch block runs = Custom message [OK]

Hint: Catch specific exceptions before general ones [OK]

Common Mistakes:

• Expecting general catch to run first
• Thinking exception is uncaught
• Ignoring exception message

4.

Identify the error in this PHP code that defines and uses a custom exception:

class MyException extends Exception {}

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

medium

A. No error; code runs fine

B. The catch blocks are in wrong order; specific should come before general

C. The throw statement syntax is incorrect

D. The class should implement Exception interface

Solution

1. Step 1: Analyze catch block order

   The first catch block catches all Exception types, including MyException, so the second catch block is unreachable.

2. Step 2: Correct catch order

   Specific exceptions like MyException must be caught before the general Exception to avoid unreachable code.

3. Final Answer:

   The catch blocks are in wrong order; specific should come before general -> Option B

4. Quick Check:

   Specific catch before general catch [OK]

Hint: Catch specific exceptions before general ones to avoid unreachable code [OK]

Common Mistakes:

• Placing general catch before specific catch
• Thinking implements is needed for exceptions
• Misunderstanding throw syntax

5.

Given this custom exception class and code, what will be the output?

class ValidationException extends Exception {
    public function getCustomMessage() {
        return "Validation failed: " . $this->getMessage();
    }
}

try {
    throw new ValidationException("Invalid input");
} catch (ValidationException $e) {
    echo $e->getCustomMessage();
} catch (Exception $e) {
    echo "General error";
}

hard

A. Fatal error: Call to undefined method

B. Invalid input

C. General error

D. Validation failed: Invalid input

Solution

1. Step 1: Understand the custom method in exception

   The class ValidationException adds a method getCustomMessage() that returns a formatted message.

2. Step 2: Check which catch block runs and output

   The thrown exception is ValidationException, so the first catch block runs and echoes the custom message.

3. Final Answer:

   Validation failed: Invalid input -> Option D

4. Quick Check:

   Custom method called on caught exception [OK]

Hint: Call custom methods on caught custom exceptions [OK]

Common Mistakes:

• Expecting default getMessage() output only
• Thinking general catch block runs first
• Assuming method does not exist