> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
>
> Again Bloch advocates documenting all exceptions in javadoc including
> unchecked exceptions using the @throws tag.
>
The @throws clause is put in, and the exceptions thrown are IllegalArgument
exceptions that have *both* the name of the argument and the reason why it
is not legal (i.e. it is null).
That satisfies the documentation aspects.
However, regarding NullPointerException vs. IllegalArgumentException, let
me delve into a bit more reasoning.
I have developed many applications where somewhere deep inside the
internal logic of the app, a NullPointerException was thrown. Nine times
out of ten, the NPE was because of some unchecked argument in some method.
For example:
class ExampleNPEFactory
{
private String m_message;
public void setMessage( String message )
{
m_message = message;
}
public String getMessage()
{
return m_message;
}
public String doSomethingWithMessage()
{
return getMessage().toUpper();
}
}
Client code would perform an operation on the doSomethingWithMessage()
method, assuming the message was set by some other class. Either that,
or they assumed that Java behaves like C++, and would provide a default
empty string (I know I have made that mistake when I first started using
Java).
Bottom line is that until setMessage() is called, that class will be a
breeding ground for NPEs. We would be able to protect ourselves from
NPEs in this case by *both* providing a default (m_message="") *and*
testing the argument of the setMessage() method. Only doing one of
those would not fix the problem.
When I see the NPEs, I look for code constructs that resemble the above
ExampleNPEFactory--which is a waste of time if it is thrown from a method
that checks its arguments. What's worse is that I have seen way too
many examples of poor use of the NullPointerException. That is why I
place it in the realm of JVM thrown exceptions and not "my code" thrown
exceptions.
When I see an IllegalArgumentException, I know the fault lies with *my*
code, not the code I am calling. Typically, the programmers who take the
time to throw an IllegalArgumentException also take the time to put a
reasonable explanation as to why it is illegal (at least in my little
universe, your mileage may vary). If a method/constructor cannot have
any null arguments, it is _illegal_ to pass one in. Therefore, I have
the proper justification for the IllegalArgumentException.
BTW, There are a few other developers who have been out there for a while
who share my viewpoint. It seems that they are on the Jakarta Commons
list, and not here ;P
That is why I favor IAE over NPE any day of the week--even if Sun does
it. I mean, would you base your next project on Visual Basic just because
"everyone else is doing it" or "it is the standard"?
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