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Error Handling
- So far, in the examples we have discussed,
there has been little room for user error. That is, for the most
part, if there is an error in the program it is our own fault rather
than some unforeseen user blunder such as entering letters into a
price field or a URL which does not exist. These types of errors
can never be exactly programmed around because it is impossible to
handle every weird thing that a user might do. We can handle
programmatic errors by simply writing error-free code, but we
cannot assure that run-time errors will not break our program.
- Thus, run time errors are just as
important to deal with as errors in your programming code. In fact,
they are often more important since your users will not be able to find
the bug and recompile the program like you will be able to do. At
run time, it is too late to debug.
- In order to handle the exceptional cases in
which the user enters data which would cause your program to crash,
Java provides a hearty exception handling methodology to
catch erroneous input, try several methods to deal with
it, and in the worst case, gracefully exit the program.
- So how does Java deal with exceptions in the
program?
- Well specifically, when an error occurs,
Java will encapsulate all the information about the error in a
special error object.
- Thus, rather than choke on the error, the
routine which generates the error will look for an event
handler object which can deal with the unexpected problem.
- The event handler object will look at the
error event object and decide what to do from there.
- Your job is to facilitate this methodology by
creating the logic for the exchange of error information between error
prone routines and error handlers and the logic that the error handlers
will use to sort through the problem.
Additional Resources:
Building a JAR File
Table of Contents
Throwing Errors
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