The Cafes » 2010 » April

Is req a request or a requisition?

Is res a response, a reservation, a resume, or a result?

Is def a default or a definition?

Is rng a range or a random number generator?

Is v1 version 1 or value 1?

Is e an event, an entity, or an exception?

Is f a file or a float?

Is lst a list or the least value?

Is temp a temporary variable or a temperature reading?

Is rep a representation, a representative, a repetition, or a reputation?

Is tm a time or a trademark? Or even another temporary variable? And if it is a time, is it a timestamp, a time of day, or a duration? (These are three very different things.)

Is admin an administrator, an administrative assistant, or a system administrator?

In context, you can usually figure these things out, but you have to think about them. That’s inefficient. Far better to just spell out what you mean from the get go.
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Every time the subject of checked versus runtime exceptions comes up, someone cites Bruce Eckel as an argument by authority. This is unfortunate, because, as much as I like and respect Bruce, he is out to sea on this one. Nor is it merely a matter of opinion. In this case, Bruce is factually incorrect. He believes things about checked exceptions that just aren’t true; and I think it’s time to lay his misconceptions to rest once and for all.

Let’s see exactly what Bruce’s mistake is. The following is an extended selection from Thinking in Java, 4th edition, pp. 490-491:

An exception-handling system is a trapdoor that allows your program to abandon execution of the normal sequence of statements. The trapdoors used when an “exceptional condition” occurs, such that normal execution is no longer possible or desirable. Exceptions represent conditions that the current method is unable to handle. The reason exception-handling systems were developed is because the approach of dealing with each possible error condition produced by each function call was too onerous, and programmers simply weren’t doing it. As a result, they were ignoring the errors. It’s worth observing that the issue of programmer convenience in handling errors was a prime motivation for exceptions in the first place.

One of the important guidelines in exception handling is “Don’t catch an exception unless you know what to do with it.” In fact, one of the important goals of exception handling is to move the error-handling code away from the point where the errors occur. This allows you to focus on what you want to accomplish in one section of your code, and how you’re going to deal with problems in a distinct separate section of your code. As a result, your mainline code is not cluttered with error-handling logic, and it’s much easier to understand and maintain. Exception handling also tends to reduce the amount of error-handling code, by allowing one handler to deal with many error sites.

Checked exceptions complicate the scenario a bit, because they force you to add catch clauses in places where you may not be ready to handle an error. This results in the “harmful if swallowed” problem:

try {
// ... to do something useful
} catch (ObligatoryException e) {} // Gulp!

Do you see the mistake? It’s a common one. (more…)