Exception hierarchy in .NET in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Exception hierarchy in .NET

Start: Exception occurs

↓

Is it a System.Exception?

↓

Is it SystemException?

↓

Specific Exception Type

↓

Catch or Propagate

↓

End

When an error happens, .NET checks if it is an Exception, then narrows down to SystemException or ApplicationException, then to specific types, deciding how to handle it.

Execution Sample

C Sharp (C#)

try {
  throw new ArgumentNullException("param");
} catch (Exception e) {
  Console.WriteLine(e.GetType().Name);
}

Throws an ArgumentNullException and catches it as Exception, printing its type name.

Execution Table

Step	Action	Exception Type	Result	Output
1	Throw new ArgumentNullException	ArgumentNullException	Exception thrown
2	Catch block checks Exception	ArgumentNullException	Caught by Exception catch
3	Print exception type name	ArgumentNullException	Printed	ArgumentNullException
4	End of try-catch	-	-	Program continues

💡 Exception caught and handled, program continues normally

Variable Tracker

Variable	Start	After Throw	After Catch	Final
e	null	ArgumentNullException instance	ArgumentNullException instance	ArgumentNullException instance

Key Moments - 2 Insights

Why does the catch block catch ArgumentNullException when it says catch(Exception e)?

Because ArgumentNullException inherits from Exception, so catch(Exception e) catches all exceptions derived from Exception as shown in execution_table step 2.

What is the difference between SystemException and ApplicationException?

SystemException is for system errors (like ArgumentNullException), ApplicationException is for user-defined exceptions. The hierarchy narrows exceptions into these categories as in concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output printed at step 3?

A Exception

B ArgumentNullException

C NullReferenceException

D No output

💡 Hint

Check the Output column at step 3 in execution_table

At which step does the exception get caught?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the Result column in execution_table where it says 'Caught by Exception catch'

If we throw a custom exception inheriting from ApplicationException, which catch block would catch it?

A Only catch(ApplicationException e)

B Only catch(SystemException e)

C catch(Exception e)

D No catch block

💡 Hint

Refer to concept_flow and key_moments about inheritance and catch blocks

Concept Snapshot

Exception hierarchy in .NET:
- Base: System.Exception
- Two main branches: SystemException (system errors), ApplicationException (user-defined)
- Specific exceptions inherit from these
- catch(Exception e) catches all exceptions
- Use specific catches for finer control

Full Transcript

In .NET, exceptions form a hierarchy starting from System.Exception. When an error occurs, the runtime checks if it is an Exception, then narrows down to SystemException or ApplicationException, and then to specific exception types like ArgumentNullException. In the example, throwing ArgumentNullException is caught by a catch block for Exception because ArgumentNullException inherits from Exception. This shows how catch blocks can catch exceptions of derived types. SystemException is for system errors, ApplicationException for user-defined errors. Understanding this hierarchy helps write better error handling code.