corner case : Java Glossary

by Roedy Green ©1996-2009 Canadian Mind Products
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corner case

Corner cases are the bane of computer programming. They are usually where you find bugs. Very often in processing a file, the first and last records have to be specially processed in some same. These would not be called corner cases, since the code is exercised every time you run the programs. Corner cases would include:

Does this code work for the empty String, null, 0 or a set of 0 elements?
Does this code work for Integer.MIN_VALUE and Integer.MAX_VALUE?
Does this code work if there are duplicate values?
Does this code work for bytes with the high bit on?
If the code demands points, what happens if three of the points are co-linear?

Normally you write your code for the ordinary case, then when you are done check if the corner cases work too. If they don’t, and your code requires all manner of special case fudging, chances are you can change the basic algorithm so most of the corner case code comes out in the wash without special handling. Sometimes you can deal with a freakish case entirely separately so it does not pollute the main logic, slowing down usual case processing.

Even the famous programmers can be thrown for a loop by corner cases. A corner case bug in binary search took two decades to be discovered.

average: how even simple code fails on corner cases
primitive

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