EXCEPTION HANDLING Byju Veedu http download oracle comjavasetutorialess

EXCEPTION HANDLING Byju Veedu http: //download. oracle. com/javase/tutorial/ess ential/exceptions/index. html

What is an exception? • An event that occurs during the execution of a program that interrupts the normal flow of execution. • Errors are serious conditions from which we better avoids recovery of the program. • Exceptions are mid-error conditions that rather than terminating the program , we can handle such exceptions and continue program execution

Exception hierarchy Java. lang. Object Java. lang. Throwable Java. lang. Error Java. lang. Exception Java. lang. IOException Java. lang. Runtime. Exception

Runtime exceptions • Exceptions that can be thrown during the normal operation of JVM • Compiler doesn’t force you to catch or specify runtime exceptions although you can. • Eg: Null. Pointer. Exception Class. Cast. Exception Arithmetic. Exception

Checked Exceptions • Checked exceptions are not runtime exceptions and are checked by the compiler. Compiler checks that these exceptions are caught or specified. • Eg: IOException SQLException Class. Not. Found. Exception

Example public class Exception. Demo { public static void main(String[] args) { int x, y; try { x = 0; y = 10; int div = y / x; } catch (Arithmetic. Exception e) { System. out. println("Exception : "+e. get. Message()); }catch (Exception e) { e. print. Stack. Trace(); } } }

Exception handling • Try Use the try statement with the code that might throw exception • Catch Specify the exception to catch and the code to execute if the specified exception is thrown. • Finally Used to define a block of code that we always want to execute, regardless of whether an exception is thrown or not. • Throw Used for throwing exceptions. (Usually a user defined exception). • Throws Lists the type of exceptions a method can throw , so that the callers of the method can guard themselves against those exceptions.

Advantages • Separating Error-Handling Code from "Regular" Code • Propagating Errors Up the Call Stack • Grouping and Differentiating Error Types

Best practices • Catch runtime exceptions only if necessary. Otherwise throw it out and catch at the end of execution and log it. • Create your own exception class to catch more details of an exception and use it. • Choose a proper exception propagation model that suites your program execution. • Don’t leave an empty catch block. This suppresses the exception and user won’t know any exception occurred or not. Use a proper logging mechanism to log the exception.

Hands-on • Use of try-catch blocks • Handling checked exceptions • Use of throw and throws • Creating user defined exception classes • Example of error

References • http: //download. oracle. com/javase/tutorial/essential/excep tions/index. html • http: //www. artima. com/designtechniques/exceptions. html