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1
An Exception is…
An unusual, often unpredictable event, detectable by software or hardware, that requires special processing
An exception handler is a section of program code
that is executed when a particular exception occurs.
2
Why have exception handlers?
With no exception handler for an exception, your program ends at the point of the exception (with no user understandable data from the O/S)
With an exception handler, you can handle the unusual condition in an understandable way
3
Try/Catch/Throw
Try: The block of code monitored for exceptions
Catch: The block of code following the try block handles an exception type
Throw: When an exception is detected, you throw an exception type
4
The try-catch Statement
try Block (exception can be thrown within this block or any called functions)catch (FormalParameter1) Blockcatch (FormalParameter2)
TryCatchStatement
How one part of the program catches and processes the exception that another part of the program throws.
FormalParameterDataType VariableName
…
5
Execution of try-catch
No statements throw
an exception
Statement following entire try-catch
statement
A statement throws
an exception
Exception Handler
Statements to deal with exception are executed
Control moves directly to exception handler
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O/S (Unix) or you can throw exceptions
O/S thrown examples No storage available for new request, divide by zero
User thrown exceptions Using the throw statement