Exception hierarchy in .NET in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a custom exception class that inherits from the base exception class.

C Sharp (C#)

public class MyCustomException : [1] {
}

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

AException

BSystemException

CApplicationException

DBaseException

Attempts:

3 left

💡 Hint

Common Mistakes

Inheriting from SystemException instead of Exception

Using a non-existent base class like BaseException

The base class for all exceptions in .NET is Exception. Custom exceptions should inherit from it.

2fill in blank

medium

Complete the code to catch all exceptions derived from the base exception class.

C Sharp (C#)

try {
    // some code
} catch ([1] ex) {
    Console.WriteLine(ex.Message);
}

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

ASystemException

BBaseException

CApplicationException

DException

Attempts:

3 left

💡 Hint

Common Mistakes

Catching SystemException only catches system exceptions, not all exceptions.

Using a non-existent class like BaseException.

Catching Exception will catch all exceptions derived from it, which includes all standard exceptions.

3fill in blank

hard

Fix the error in the code by choosing the correct base class for a custom exception.

C Sharp (C#)

public class DataNotFoundException : [1] {
    public DataNotFoundException(string message) : base(message) {}
}

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

AApplicationException

BSystemException

CException

DErrorException

Attempts:

3 left

💡 Hint

Common Mistakes

Using SystemException which is meant for system exceptions.

Using a non-existent class like ErrorException.

Custom exceptions should inherit from ApplicationException or directly from Exception. Here, Exception is the best choice for custom exceptions as ApplicationException is generally not recommended for new code.

4fill in blank

hard

Fill both blanks to create a dictionary mapping exception types to their descriptions.

C Sharp (C#)

var exceptionDescriptions = new Dictionary<string, string> {
    {"[1]", "Base class for all exceptions"},
    {"[2]", "Base class for system exceptions"}
};

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

AException

BSystemException

CApplicationException

DBaseException

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing ApplicationException with SystemException.

Using a non-existent class like BaseException.

Exception is the base class for all exceptions, and SystemException is the base class for system exceptions.

5fill in blank

hard

Fill all three blanks to create a LINQ query that selects exception names and filters system exceptions.

C Sharp (C#)

var systemExceptions = from ex in exceptions
                       where ex is [1]
                       select new { Name = ex.GetType().[2] , Type = ex.[3] };

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

ASystemException

BName

CGetType

DMessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using GetType() instead of the Name property for the type name.

Using the wrong property for the message.

The query filters exceptions that are SystemException or derived. It selects the exception's type name using the Name property and the exception message.

Practice

1. Which class is the base class for all exceptions in .NET?

easy

A. System.Error

B. System.Exception

C. System.ApplicationException

D. System.SystemException

Solution

1. Step 1: Understand the exception hierarchy

   All exceptions in .NET inherit from a common base class to unify error handling.

2. Step 2: Identify the root base class

   The root base class for all exceptions is System.Exception, from which other exceptions derive.

3. Final Answer:

   System.Exception -> Option B

4. Quick Check:

   Base exception class = System.Exception [OK]

Hint: Remember: All exceptions come from System.Exception [OK]

Common Mistakes:

• Confusing System.SystemException as the base
• Thinking System.ApplicationException is the root
• Assuming System.Error exists in .NET

2. Which of the following is the correct syntax to catch a specific exception type ArgumentNullException in C#?

easy

A. catch (ArgumentNullException e) { }

B. catch ArgumentNullException (e) { }

C. catch (Exception e) { }

D. catch ArgumentNullException { }

Solution

1. Step 1: Recall catch block syntax

   In C#, to catch a specific exception, use catch (ExceptionType variable) syntax.

2. Step 2: Match the correct syntax for ArgumentNullException

   The correct syntax is catch (ArgumentNullException e) { }, which declares the exception type and variable.

3. Final Answer:

   catch (ArgumentNullException e) { } -> Option A

4. Quick Check:

   Correct catch syntax = catch (ExceptionType e) [OK]

Hint: Use parentheses around exception type and variable in catch [OK]

Common Mistakes:

• Omitting parentheses around exception type
• Using wrong order like catch ExceptionType (e)
• Not declaring a variable for the exception

3. What will be the output of the following C# code?

try {
    int[] arr = new int[2];
    Console.WriteLine(arr[5]);
} catch (IndexOutOfRangeException e) {
    Console.WriteLine("Index error caught");
} catch (Exception e) {
    Console.WriteLine("General error caught");
}

medium

A. General error caught

B. Compilation error

C. No output, program crashes

D. Index error caught

Solution

1. Step 1: Identify the exception thrown

   Accessing index 5 in an array of size 2 throws IndexOutOfRangeException.

2. Step 2: Check which catch block handles it

   The first catch block specifically catches IndexOutOfRangeException, so it runs and prints "Index error caught".

3. Final Answer:

   Index error caught -> Option D

4. Quick Check:

   Specific catch runs before general [OK]

Hint: Specific exceptions catch before general ones [OK]

Common Mistakes:

• Thinking general Exception catch runs first
• Assuming program crashes without catch
• Confusing IndexOutOfRangeException with ArgumentException

4. Identify the error in this code snippet:

try {
    int x = int.Parse("abc");
} catch (FormatException) {
    Console.WriteLine("Format error");
} catch {
    Console.WriteLine("General error");
}

medium

A. Catch-all block must be last

B. Catch blocks order is incorrect

C. No error, code is correct

D. Missing exception variable in catch blocks

Solution

1. Step 1: Review catch block syntax

   Catch blocks can omit the exception variable if not used, which is valid here.

2. Step 2: Check catch block order

   The specific FormatException catch is before the general catch-all block, which is correct.

3. Final Answer:

   No error, code is correct -> Option C

4. Quick Check:

   Catch-all last and variable optional [OK]

Hint: Catch-all must be last; variable optional in catch [OK]

Common Mistakes:

• Thinking catch-all must have variable
• Placing catch-all before specific catch
• Assuming variable is mandatory in catch

5. You want to catch all exceptions except NullReferenceException and handle them differently. Which approach correctly implements this in C#?

hard

A. Use a catch block for Exception and rethrow if NullReferenceException

B. Use a single catch block for Exception and check exception type inside

C. Use two catch blocks: one for NullReferenceException, one for Exception

D. Use a catch block for NullReferenceException only

Solution

1. Step 1: Understand the requirement

   We want to handle all exceptions except NullReferenceException differently, so we must detect and exclude it.

2. Step 2: Evaluate approaches

   Use a catch block for Exception and rethrow if NullReferenceException uses a general catch for Exception, then rethrows if the exception is NullReferenceException, effectively excluding it from handling.

3. Final Answer:

   Use a catch block for Exception and rethrow if NullReferenceException -> Option A

4. Quick Check:

   Rethrow to exclude specific exceptions [OK]

Hint: Rethrow specific exceptions inside general catch [OK]

Common Mistakes:

• Catching NullReferenceException first but not rethrowing
• Handling all exceptions in one catch without rethrow
• Using only NullReferenceException catch block