Exception handling
- 1. CIS 2403- Object Oriented Programming 1 Exception Handling CIS 2403 Object Oriented Programming
- 2. CIS 2403- Object Oriented Programming 2 Understanding Exceptions • An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions. • Exceptions are caused by errors in program logic or insufficient system resources.
- 3. CIS 2403- Object Oriented Programming 3 Example
- 4. CIS 2403- Object Oriented Programming 4 Understanding Exceptions • The programs you write can generate many types of potential exceptions, including when: Your program asks for user input, but the user enters invalid data. The program attempts to divide an integer by zero. You attempt to access an array with a subscript that is too large or too small. You calculate a value that is too large for the answer’s variable type.
- 5. CIS 2403- Object Oriented Programming 5 Understanding Exceptions • These errors are called exceptions because presumably they are not usual occurrences; they are “exceptional.” • The object-oriented techniques used to manage such errors make up the group of methods known as exception handling. If you do not handle an exception, the running program terminates abruptly.
- 6. CIS 2403- Object Oriented Programming 6 Traditional Error Handling • Programmers had to deal with error conditions long before object-oriented methods were conceived • This code successfully prevents division by zero, but it does not really “handle an exception” because no Exception class object is created.
- 7. CIS 2403- Object Oriented Programming 7 Traditional Error Handling • If a user enters 0 for gallonsOfGas in only one case out of 1,000, then the if statement is executed unnecessarily 999 times! • In that case, it is more efficient to eliminate the if test and instantiate an Exception object when needed.
- 8. CIS 2403- Object Oriented Programming 8 Handling Exceptions • A program can catch exceptions by using a combination of the try, catch, and finally blocks. The try block identifies a block of code in which an exception can occur. The catch block identifies a block of code, known as an exception handler, that can handle a particular type of exception. The finally block identifies a block of code that is guaranteed to execute.
- 9. CIS 2403- Object Oriented Programming 9 The Try Block • The first step is to enclose the code that might throw an exception within a try block. • To associate an exception handler with a try block, you must put a catch block after it
- 10. CIS 2403- Object Oriented Programming 10 The catch Blocks • You associate exception handlers with a try block by providing one or more catch blocks directly after the try block. • The catch block contains code that is executed if and when the exception handler is invoked.
- 11. CIS 2403- Object Oriented Programming 11 The finally Block • The finally block always executes when the try block exits.
- 12. CIS 2403- Object Oriented Programming 12 Let’s Apply
- 13. CIS 2403- Object Oriented Programming 13 Resources • Farrell.. Microsoft® Visual C# 2012: An Introduction to Object-Oriented Programming, International Edition, 5th Edition. Cengage Learning UK, 2013. • Oracle, Java Documentation: https://docs.oracle.com/javase/tutorial/ess ential/exceptions/index.html