Exception Handling

1. 8/13/2012 Komar Associates 1 Exception Handling Joe Komar

2. 8/13/2012 Komar Associates 2 Overview When to use exception handling Java Exception Handling try blocks Throwing and catching exceptions Constructors, finalizers and exception handling finally block printStackTrace and getMessage

3. 8/13/2012 Komar Associates 3 Exception Handling Similar to the established C++ methodology Synchronous exceptions (divide by zero) versus asynchronous exceptions (interrupts) Improves a program�s �fault tolerance� Build in from the beginning

4. 8/13/2012 Komar Associates 4 Exceptions Exception -- �thrown� by program or runtime environment and can be �caught� and handled Error -- similar to an exception but represents an unrecoverable situation and should not be handled Java: Exception and Error classes derived from the Throwable class Specific exceptions and errors derived from their classes Pages 666-668 for diagram of how the inheritance hierarchy goes for exceptions and errors In real world, need to handle exceptions otherwise program bombs -- a lot of programmer time spent on this.Pages 666-668 for diagram of how the inheritance hierarchy goes for exceptions and errors In real world, need to handle exceptions otherwise program bombs -- a lot of programmer time spent on this.

5. 8/13/2012 Komar Associates 5 Exception Execution Flow Distinguish Exception flow from Normal flow Debugging is made easier (pinpoint errors) Java API classes often throw exceptions, letting the programmer decide what to do with them �Normal� flow is typically 20% of the total code Some programs should never abnormally abort Deal with exceptions by: choosing not to handle them (abnormal abort) handle the exception where it occurs handle the exception at another point (throws) Separate the �normal� flow from the �exception� flow makes for better designed and more readable programsSeparate the �normal� flow from the �exception� flow makes for better designed and more readable programs

6. 8/13/2012 Komar Associates 6 Use Exception Handling To.. process where method is unable to complete its task process where components aren�t geared to handle them process where components are widely used and cannot handle themselves on large projects to handle exceptions in a uniform way

7. 8/13/2012 Komar Associates 7 The try Statement The try statement identifies a block of statements that may throw an exception There can be a number of catch blocks following the try block that can process different types of errors