3.C#
Download as PPTX, PDF0 likes249 views
The document discusses exception handling in .NET. It explains that exceptions derive from System.Exception and that a try block is used to wrap code that may throw exceptions. If an exception occurs, control jumps to the first matching catch block. If no catch block matches, the program terminates with an error. Catch blocks define code to handle specific exception types. A finally block always executes to clean up resources regardless of exceptions. Well-defined exception classes make errors easier to handle.
3.C#
- 2. Exception Handling in .net Exceptions are types that all ultimately derive from System.Exception. Use a try block around the statements that might throw exceptions. Once an exception occurs in the try block, the flow of control jumps to the first associated exception handler that is present anywhere in the call stack. In C#, the catch keyword is used to define an exception handler. If no exception handler for a given exception is present, the program stops executing with an error message.
- 3. Syntax try { // code that requires common cleanup or // exception-recovery operations } catch (InvalidOperationException) { //code that recovers from an InvalidOperationException // (or any exception type derived from it) } catch (SomeOtherException) { // code that recovers from an SomeOtherException // (or any exception type derived from it) } catch { // code that recovers from any kind of exception // when you catch any exception, you usually re-throw throw; } finally { // code that cleans up any operations started // within the try block. This code ALWAYS executes. }
- 4. try block A try block contains code that requires common cleanup or exception-recovery operations. The cleanup code should be put in a single finally block. The exception recovery code should be put in one or more catch blocks. Create one catch block for each kind of type you want to handle. A try block must have at least one catch or finally block.
- 5. catch block A catch block contains code to execute in response to an exception. If the code in a try block doesn’t cause an exception to be thrown, the CLR will never execute the code in any of its catch blocks. You may or may not specify a catch type in parantheses after catch : The catch type must be of type System.Exception or a type that derived from System.Exception If there is no catch type specified, that catch block handles any exception. This is equivalent to having a catch block that specifies System.Exception as a catch type. CLR searches for a matching catch type from top to bottom. If CLR cannot find any catch type that matches the exception, CLR continues searching up the callstack to find a catch type.
- 6. Once the catch block that matches the exception is found, you have 3 choices: Re-throw the same exception Throw a different exception, giving richer exception information to code. Let the code continue from the bottom of the catch block In choices 1-2, an exception is thrown and code starts looking for a catch block whose type matches the exception thrown In choice 3, the finally block is executed You can also specify a variable name like catch(Exception e) to access information specific to the exception.
- 7. finally block GC does automatic memory clean-up, it only cleans up if there are no references kept on the object. Thus, memory leaks can occur if programmers carelessly keep references to unwanted objects. C# provides the finally block, which is guaranteed to execute regardless of whether an exception occurs. If the try block executes without throwing, the finally block executes. If the try block throws an exception, the finally block still executes regardless of whether the exception is caught. This makes the finally block ideal to release resources from the corresponding try block.
- 8. Exception Classes in C# C# exceptions are represented by classes. The exception classes in C# are mainly directly or indirectly derived from the System.Exception class. Some of the exception classes derived from the System.Exception class are the System.ApplicationException and System.SystemE xception classes. The System.ApplicationException class supports exceptions generated by application programs. So the exceptions defined by the programmers should derive from this class. The System.SystemException class is the base class for all predefined system exception.
- 9. System.Exception Properties Class Exception’s properties are used to formulate error messages indicating a caught exception. Property Message stores the error message associated with an Exception object. Property StackTrace contains a string that represents the method-call stack. When an exception occurs, a programmer might use a different error message or indicate a new exception type. The original exception object is stored in the InnerException property. Other properties: HelpLink specifies the location of a help file that describes the problem. Source specifies the name of the application or object that caused the exception. TargetSite specifies the method where the exception originated.
- 10. Defined Exception Exception Class Description System.IO.IOException Handles I/O errors. System.IndexOutOfRangeException Handles errors generated when a method refers to an array index out of range. System.ArrayTypeMismatchException Handles errors generated when type is mismatched with the array type. System.NullReferenceException Handles errors generated from deferencing a null object. System.DivideByZeroException Handles errors generated from dividing a dividend with zero. System.InvalidCastException Handles errors generated during typecasting. System.OutOfMemoryException Handles errors generated from insufficient free memory. System.StackOverflowException Handles errors generated from stack overflow.
- 11. Questions ??