CS608 Lecture Notes Visual Basic.NET Programming Object-Oriented Programming Classes & Objects – Advanced Topics Part III (Error Handling) (Part III of III) (Lecture Notes 2C) Prof. Abel Angel Rodriguez2 CHAPTER 7 CLASSES & OBJECTS -ADVANCED CONCEPTS (CONT)......................................... 3 7.1 Error Handling in VB.NET............................................................................................................................................................... 3 7.1.1 General Discussion on Errors........................................................................................................................................................ 3 Syntax Errors ..................................................................................................................................................................................... 3 Logical Errors .................................................................................................................................................................................... 3 Run-Time Errors ................................................................................................................................................................................ 3 7.2 Exception in VB.NET ........................................................................................................................................................................ 6 7.2.1 Exceptions Basics in VB.NET ...................................................................................................................................................... 6 The Exit Try Statement ...................................................................................................................................................................... 8 7.2.2 The VB.NET Exception Class .................................................................................................................................................... 10 Introduction to the VB.NET Exception Class .................................................................................................................................. 10 Trapping all Errors using the VB.NET Exception Class.................................................................................................................. 11 7.2.3 Trapping for Specific Error Using other Exception Classes Provided by VB.NET .................................................................... 15 Trapping for Specific Error using the Exception Classes ................................................................................................................ 16 7.2.4 Trapping for Many Error using Multiple Catch Blocks .............................................................................................................. 22 7.2.5 The Throw Statement .................................................................................................................................................................. 24 Error Handling Summarized ............................................................................................................................................................ 24 Raising our own errors ..................................................................................................................................................................... 24 Using the Throw Statement.............................................................................................................................................................. 25 7.3 Shared Methods ............................................................................................................................................................................... 30 7.3.1 Overview & Discussion .............................................................................................................................................................. 30 7.3.2 Shared Methods .......................................................................................................................................................................... 31 7.4 Shared Variables .............................................................................................................................................................................. 32 7.4.1 Overview ..................................................................................................................................................................................... 323 Chapter 7 Classes & Objects -Advanced Concepts (Cont) 7.1 Error Handling in VB.NET 7.1.1 General Discussion on Errors  In our review of VB.NET we discussed the various types of errors that can occur in a program.  There are three varieties of programming errors: 1. Syntax 2. Logical 3. Run-Time Syntax Errors  Syntax Errors – Errors generated due to the code not following the rules of the language  These errors usually involve improper punctuation, spelling or format  These problems are easier to solve since the compiler identifies the erroneous statement by displaying a BLUE Wiggly Line under the incorrect VB.NET Statement.  To resolve this problem, you just have to review the rules of the language for that statement and make sure you are writing the statement properly Logical Errors  Logical Error – The program is not doing what is supposed to do. .  The algorithm fails to solve the problem the program was written to resolve  These problems are very difficult to solve since you need to re-think and go back to the planning phase and review the Algorithm. Run-Time Errors  Run Time Errors – These are programs that occur when the program is executing. The program passed the syntax or compiler test but fails during execution. .  These errors can be caused by the user entering a wrong data type via keyboard or performing some illegal operation, program logic not doing what is supposed to do, or system errors.  These problems are usually caused by improper arithmetic execution, attempting to access recourses that are not available etc  These problems are difficult to solve since they only show up when the program runs.  When a run-time error is generated, the built-in default Error handling mechanism of VB.NET will trap the error and terminate the