Le 08/08/2011 21:25, Phil Steitz a écrit :
On 8/8/11 12:03 PM, Gilles Sadowski wrote:
Hi.
[...]
Cases such as this would fall in the "illegal argument" category.
Thus:
throw new OutOfRangeException(index, 0, parameters.length);
or, to get a more detailed message,
OutOfRangeException e = new OutOfRangeException(index, 0, parameters.length);
e.addMessage(INDEX, index);
throw e;
Of course, "OutOfRangeException" cannot inherit from both
"IllegalArgumentException" and "IndexOutOfBoundsException"...
I thought about that, but would prefer to throw
ArrayIndexOutOfBoundsException because that is really what is going
on and I would prefer to throw the standard exception. Ideally, I
would like to throw that with a message reporting the value and the
length of the array. So, there are three choices:
0) throw AIOB with no message
1) subclass and throw with localized message - my suggestion above
2) OutOfRangeException
I like 1) the best and since we have decided to deprecate the
MathRuntimeException, note that it applies to all of the other
standard exceptions generated by MathRuntimeException's createXxx
methods that have not yet been subclassed. I think we should follow
the generally accepted practice to favor standard exceptions, so
that means we are going to have to create wrappers for all that we
use. I am willing to help with this. In this case, I will go ahead
and add the MathArrayIndexOutOfBoundsException that will be an
ArrayIndexOutOfBoundsException if others are OK with this. Note
that doing this will allow us to handle situations where IAE is not
appropriate (essentially why AIOB does not itself extend IAE).
As I understand it, AIOB is a low-level exception that is thrown by the JVM
checking an array access:
---CUT---
i = 3;
double a = arr[i]; //<--- can throw AIOB
---CUT---
However, I don't see how a user code can be similar to this: When you check
the index in your above code, you didn't try to access the array yet. You've
detected that it won't work because the index value is "out of range", thus,
"illegal".
When we are about to access an array, we can perform the check. We
can either just allow the JVM to throw the RTE (essentially my
option 0) above) or provide some more context info to the user (my
option 1) or throw an entirely different exception (option 2). It
is good to throw some kind of AIOB when that is in fact what is
going on, as it provides more context info than just "something is
out of range" (OutOfRangeException).
As shown above, you can add as many items of context information as you want
with the exception context. The example I've suggested above will create a
message that will print something like:
OutOfRangeException: 3 out of [0, 2] range: index (3)
I find this quite clear; but we can even add another "LocalizedFormats" like
"ARRAY_INDEX" if you really need the above to read:
OutOfRangeException: 3 out of [0, 2] range: array index (3)
However, the crux of my point is that the "array" part is an implementation
detail. A user should not care that a sequence of data is stored in an array
of primitives or in a "List" or a CM's "RealVector". The real info is that
the index used to access the data must fall within a range; if not, it is
"out of range".
Then, what I was saying in the previous post is that we should not throw
AIOB because we are not the JVM. In Java, that exception is a *result* of
"calling" the [] operator. Your test happens before calling it; and an
"OutOfRangeException" is as accurate as necessary but not more (so as not to
leak about the internals of a class).
I can see that we are not going to agree on this. I prefer standard
exceptions and it is generally accepted best practice to favor
them. To say that only the JDK should throw JDK RTEs is silly,
IMO. We are going to have the same problem with ConcurrentMod, IO,
EOF and the others currently created by MathRuntimeException. Are
we going to try to shoehorn every use of any of these into some kind
of "some number too small" or other special [math] exceptions? What
do others think about this?
Well, I basically gave up on exceptions :-(
Here are my views, but I would not enforce them anymore on anybody.
I consider JDK exceptions could be used, and that we needed the
localization (I know the view of everyone on this, so don't argue
again). this was the reason for the createXxx exception, which had
signatures corresponding to standard exceptions, and did subclass them
with anonymous classes that override the JDK standard getMessage and
getLocalizedMessage methods. This way, we combined both needs.
Once again, this are only my own views. Do what you want with them.
Luc
Phil
Gilles
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