Le 08/08/2011 23:43, Gilles Sadowski a écrit :
[...]
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.
Well, I agree with your views and I am proposing that as a
compromise, we simply replace the createXxx methods in
MathRuntimeExceptions with exceptions like MathArithmeticException,
MathIllegalStateException, etc.
This is done already!!!
I am proposing in this case to add
MathArrayIndexOutOfBoundsException (extending AIOB so you can
I do not understand why, in other circumstances, you are against propagating
low-level error conditions ("number too small" being your favorite example)
but here you find no problem exposing an implementation detail ("array")...
advertise the real thing) and I will even volunteer to fill in the
remaining ones from createXxx so we don't have to argue about this
any more.
OK, I see that you just *like* antiques.
So let's say that you will create as many exceptions as you deem nice
(although one of the first conditions *I* had been set was to avoid a
bloated exception package...). I give up arguing all over again.
To definitely close the exception debate, can we now set to resolve the
issue of deprecating the (old) "MathRuntimeException" and "MathException"
classes and purge all checked exceptions? These are the things which really
matter and which I insist on keeping from the string of previous
compromises.
Yes (but consider it non-binding).
Luc
Gilles
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