Exceptions: When Things Go Wrong
It is not a matter of IF but WHEN things will go wrong in a computer program. Sometimes there are bugs, errors of one form or another. There are also unforeseen use cases. You can never assume a computer program is perfect. Exception-Handling helps us to catch erroneous events and devise means of correcting them. We discuss this topic here since exception-handling can take more code than should be put into the main line of execution. In such cases, a method in an exception-handling class should be called. Exception handling mechanisms allow a program to continue executing, instead of terminating it abruptly, even if an error occurs in the program.
10.2 Handling Exceptional Conditions
Traditional Error Handling
Obviously, the method in Figure 10.1 should not simply ignore the possibility that N might be 0. Figure 10.2 shows a revised version of the method, which includes code that takes action if the method’s precondition fails.
Because there is no way to compute an average of 0 elements, the revised
method decides to abort the program. Aborting the program appears to
be a better alternative than returning 0 or some other default value (like
1) as the method’s result and thereby allowing an erroneous value to
spread throughout the program. That would just compound the error.
The revised avgFirstN() method takes the traditional approach to error handling: Error-handling code is built right into the algorithm. If N
happens to be 0 when avgFirstN() is called, the following output will
be generated:
