C# Exception Hierarchy Overview

The Exception Hierarchy

• Exceptions in C# are represented by classes.
• All exceptions are subclasses of the System.Exception class.
• There are two types of exceptions.
  • ApplicationException: generated by user programs.
  • SystemException: generated by the Common Language Runtime (CLR).

Common Exceptions

• System.Exception: the root of the exception hierarchy.
• System.ArithmeticException: thrown when an arithmetic or conversion operation encounters an error.
• System.OverflowException: thrown when a checked operation overflows.
• System.ArgumentException: thrown when a method receives an invalid argument.
• System.ArgumentNullException: thrown when a method receives a null argument.
• System.IndexOutOfRangeException: thrown when an array is indexed with an invalid index.
• System.OutOfMemoryException: thrown when the available memory is insufficient.
• System.StackOverflowException: thrown when the execution stack is exhausted due to too many pending method calls.
• System.FormatException: thrown when a string or argument fails to meet a specific format.

The try-catch Block

• The try-catch block is used for handling exceptions in C#.
• It involves four keywords:
  • try: encloses the code to be checked for exceptions.
  • catch: catches the exception thrown in the try block.
  • throw: used to manually throw an exception.
  • finally: executes a statement regardless of whether an exception is thrown or not.

Manually Throwing an Exception

• Exceptions can be thrown manually using the throw keyword.
• Syntax: throw new exception_object;
• exception_object is an instance of a class derived from Exception.
• new operator creates a new object of the exception class.

Custom Exceptions

• You can create your own custom exception classes in C#.
• Custom exception classes must inherit from System.Exception or one of its derived classes.
• Custom exceptions can be thrown and handled like standard exceptions.

Example: Custom Exception Class

• Example custom exception class InvalidUserInputException:

  public class InvalidUserInputException : Exception
  {
      public InvalidUserInputException(string age) : base(age)
      {
      }
  }
  

  • This custom exception can be used to indicate invalid user input, for example, age that is not valid.
  • The constructor takes a string argument (age) representing a message describing the invalid input.
  • The custom exception class can be used like any other exception:
    • Throw: throw new InvalidUserInputException("Not in legal age!");
    • Catch: catch(InvalidUserInputException ex) { ... }

This quiz covers the C# exception hierarchy, focusing on the classification and purpose of various exceptions. Learn about the root exception class, common exceptions like System.ArgumentException and System.OverflowException, and their specific uses in application development.