Throwing exceptions in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to throw an exception with the message "Error occurred".

PHP

<?php
throw new [1]("Error occurred");
?>

Drag options to blanks, or click blank then click option'

AException

BError

CThrowable

DRuntimeException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class that does not exist or is not throwable.

Forgetting to use the 'new' keyword before the exception class.

The Exception class is the base class for all exceptions in PHP. Using throw new Exception("Error occurred") correctly throws an exception with the given message.

2fill in blank

medium

Complete the code to throw a RuntimeException with the message "Runtime error".

PHP

<?php
throw new [1]("Runtime error");
?>

Drag options to blanks, or click blank then click option'

AException

BErrorException

CRuntimeException

DLogicException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic Exception instead of a specific RuntimeException.

Using an unrelated exception class.

RuntimeException is a built-in exception class used to represent runtime errors. Throwing it with throw new RuntimeException("Runtime error") is correct.

3fill in blank

hard

Fix the error in the code to correctly throw an exception with the message "Invalid input".

PHP

<?php
throw [1]("Invalid input");
?>

Drag options to blanks, or click blank then click option'

Anew Exception

BException

CError

Dnew Error

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the 'new' keyword before the exception class.

Using the exception class name without parentheses.

When throwing an exception, you must use the new keyword before the exception class name. So throw new Exception("Invalid input") is correct.

4fill in blank

hard

Fill both blanks to throw an exception with the message "File not found" using the ErrorException class.

PHP

<?php
throw new [1]("File not found", [2]);
?>

Drag options to blanks, or click blank then click option'

AErrorException

B404

C0

DException

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong exception class.

Using an invalid error code.

The ErrorException constructor accepts a message and an error code. Using 0 as the code is common when no specific code is needed.

5fill in blank

hard

Fill all three blanks to throw a LogicException with the message "Invalid operation", code 100, and previous exception stored in $prev.

PHP

<?php
throw new [1]("Invalid operation", [2], [3]);
?>

Drag options to blanks, or click blank then click option'

AException

B100

C$prev

DLogicException

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong exception class.

Mixing up the order of arguments.

Not passing the previous exception variable.

The LogicException constructor accepts a message, a code, and a previous exception. Passing "Invalid operation", 100, and $prev correctly creates the exception.

Practice

1. What does the throw statement do in PHP?

easy

A. It catches an exception to handle an error.

B. It creates and signals an exception to indicate an error.

C. It defines a new function for error handling.

D. It stops the script without any error message.

Solution

1. Step 1: Understand the purpose of throw

   The throw statement is used to create and signal an exception when an error occurs.

2. Step 2: Differentiate from other error handling keywords

   catch handles exceptions, but throw actually creates and signals them.

3. Final Answer:

   It creates and signals an exception to indicate an error. -> Option B

4. Quick Check:

   throw = signal error [OK]

Hint: Remember: throw = create error, catch = handle error [OK]

Common Mistakes:

• Confusing throw with catch
• Thinking throw stops script silently
• Assuming throw defines functions

2. Which of the following is the correct syntax to throw an exception with the message "Error occurred" in PHP?

easy

A. throw new Exception("Error occurred");

B. throw Exception("Error occurred");

C. throw Exception new("Error occurred");

D. throw new Exception(Error occurred);

Solution

1. Step 1: Recall the syntax for throwing exceptions

   In PHP, you must use throw new Exception("message") to throw an exception with a message.

2. Step 2: Check each option for syntax correctness

   Only throw new Exception("Error occurred"); matches the correct syntax exactly. The other options either omit the new keyword, have the wrong order of keywords, or lack quotes around the message.

3. Final Answer:

   throw new Exception("Error occurred"); -> Option A

4. Quick Check:

   Correct syntax = throw new Exception(message) [OK]

Hint: Use 'throw new Exception("message")' exactly [OK]

Common Mistakes:

• Omitting the 'new' keyword
• Not quoting the message string
• Wrong order of keywords

3. What will be the output of the following PHP code?

try {
    throw new Exception("Oops!");
    echo "No error";
} catch (Exception $e) {
    echo $e->getMessage();
}

medium

A. No error

B. Fatal error

C. Exception thrown but no output

D. Oops!

Solution

1. Step 1: Analyze the try block

   The code throws an exception with message "Oops!" before the echo statement, so "No error" is never printed.

2. Step 2: Understand the catch block behavior

   The catch block catches the exception and echoes the message from the exception, which is "Oops!".

3. Final Answer:

   Oops! -> Option D

4. Quick Check:

   Exception message printed = Oops! [OK]

Hint: Exception stops try block; catch prints message [OK]

Common Mistakes:

• Expecting code after throw to run
• Thinking no output appears
• Confusing exception message with error

4. Identify the error in this PHP code snippet:

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

medium

A. Exception class is not imported.

B. Missing semicolon after throw statement.

C. Method message() does not exist; should use getMessage().

D. Catch block syntax is incorrect.

Solution

1. Step 1: Check the catch block method call

   The Exception class has a method getMessage() to get the error message, not message().

2. Step 2: Verify other syntax elements

   The semicolon after throw is present, Exception class is built-in, and catch syntax is correct.

3. Final Answer:

   Method message() does not exist; should use getMessage(). -> Option C

4. Quick Check:

   Use getMessage() to get exception text [OK]

Hint: Use getMessage() method to read exception message [OK]

Common Mistakes:

• Calling non-existent message() method
• Missing semicolons (not in this case)
• Incorrect catch syntax

5. You want to throw an exception only if a variable $age is less than 18. Which code correctly does this and catches the exception to print its message "Too young"?

hard

A. try {
if ($age < 18) {
throw new Exception("Too young");
}
} catch (Exception $e) {
echo $e->getMessage();
}

B. try {
if ($age < 18) {
throw new Exception("Too young");
}
} catch (Exception $e) {
echo "Too young";
}

C. try {
if ($age < 18) {
throw Exception("Too young");
}
} catch (Exception $e) {
echo $e->getMessage();
}

D. if ($age < 18) {
throw new Exception("Too young");
} catch (Exception $e) {
echo $e->getMessage();
}

Solution

1. Step 1: Identify correct try-catch structure

   The exception must be thrown inside a try block to be caught properly. try { if ($age < 18) { throw new Exception("Too young"); } } catch (Exception $e) { echo $e->getMessage(); } correctly wraps the throw inside try.

2. Step 2: Check exception throwing syntax and catch output

   try { if ($age < 18) { throw new Exception("Too young"); } } catch (Exception $e) { echo $e->getMessage(); } uses correct syntax throw new Exception("Too young") and prints the exception message with echo $e->getMessage();.

3. Final Answer:

   try { if ($age < 18) { throw new Exception("Too young"); } } catch (Exception $e) { echo $e->getMessage(); } -> Option A

4. Quick Check:

   Throw inside try, catch prints message [OK]

Hint: Always throw exceptions inside try blocks to catch them [OK]

Common Mistakes:

• Throwing outside try block
• Missing 'new' keyword when throwing
• Printing hardcoded message instead of exception message