Chapter 13 Exception Handling: A Deeper Look

1. Chapter 13Exception Handling: A Deeper Look

2. Things Happen

3. Terminology

4. Exception Keywords

5. Running example using System; usingSystem.Collections.Generic; usingSystem.Linq; usingSystem.Text; namespaceUsingExceptions { classProgram { staticvoid Main(string[] args) { int x = 10; int y = 5; int result; try { result = x / y; Console.WriteLine("The result is: {0}", result); } catch { Console.WriteLine("An error occurred! Better check the code!"); } finally { Console.WriteLine("Just proving that this code always runs."); } Console.ReadLine(); }}}

6. Catching Specific Exceptions

7. Hierarchy try { result = x / y; Console.WriteLine("The result is: {0}", result); } catch (System.DivideByZeroException e) { Console.WriteLine("Whoops! You tried to divide by zero!"); Console.WriteLine(e.Message); } catch (System.ArithmeticException e) { Console.WriteLine("Whoops! You tried to divide by zero!"); Console.WriteLine(e.Message); }

8. More Specific First try { result = x / y; Console.WriteLine("The result is: {0}", result); } catch (System.ArithmeticException e) { Console.WriteLine("Whoops! You tried to divide by zero!"); Console.WriteLine(e.Message); } catch (System.DivideByZeroException e) { Console.WriteLine("Whoops! You tried to divide by zero!"); Console.WriteLine(e.Message); } finally { Console.WriteLine("Just proving that this code always runs."); } Console.ReadLine();

9. Exceptions are Objects • System.Exception • Constructors • Properties • Hierarchy • http://msdn.microsoft.com/en-us/library/system.systemexception.aspx • System.Exception • System.ApplicationException(non fatal exceptions) • http://msdn.microsoft.com/en-us/library/system.applicationexception.aspx

10. Custom Exceptions

11. using System; usingSystem.Collections.Generic; usingSystem.Linq; usingSystem.Text; namespaceCustomExceptions { publicclassMyOwnException : Exception { publicMyOwnException() : base("Sergey is not welcomed here!") //Exception(string) { //this.HelpLink= "http://msdn.microsoft.com/en-us/library/system.exception.aspx"; } } classProgram { staticstringGetName() { string s = Console.ReadLine(); if (s.Equals("Sergey")) thrownewMyOwnException(); return s; }

12. staticvoid Main(string[] args) { stringtheName; try { theName = GetName(); Console.WriteLine("Hello {0}", theName); } catch (MyOwnExceptionnje) { Console.WriteLine(nje.Message); Console.WriteLine("For help, visit: {0}", nje.HelpLink); } finally { Console.WriteLine("Have a nice day!"); } Console.ReadLine(); } } }

13. 13.2 Example: Divide by Zero without Exception Handling

14. Re-throwing Exceptions classProgram { staticvoidDoSomeMath() { int x = 10, y = 0; int result; try { result = x / y; Console.WriteLine("Result is {0}", result); } catch { Console.WriteLine("Error in DoSomeMath()"); thrownewArithmeticException(); } } staticvoid Main(string[] args) { try { DoSomeMath(); } catch (ArithmeticException e) { Console.WriteLine("Hmm, there was an error in there, be careful!"); } Console.ReadLine(); } }

16. 13.3 Example: Handling DivideByZeroExceptions and FormatExceptions

21. 13.4 .NET Exception Hierarchy

22. 13.5 finally Block

32. 13.7 Exception Properties

38. 13.8 User-Defined Exception Classes