RFR [8014066] Mistake in documentation of ArrayList#removeRange

[David Holmes]

Hi Ivan,

I think we need to apply the brakes here and back up a bit :)

First of all these aren't typo fixes they are spec changes and they will 
need to go through CCC for approval.

Second point is that the condition "fromIndex >= size()" is already 
captured by the condition "if {@code fromIndex} or {@code toIndex} is 
out of range". By definition fromIndex is out-of-range if it is < 0 or 
 >= size(). So I don't see any error here even if there is some redundancy.

Third, a call a.removeRange(a.size(), a.size()) hits the normal dilemma 
of "what should be checked first?". The spec states that 
removeRange(n,n) is a no-op, so if we do that check first we just 
return, even for bad things like removeRange(-5, -5). Of course if we 
check all the preconditions first then we would in fact throw the IOOBE. 
I'm in the camp that says we check preconditions first because it 
detects silly mistakes sooner.

Fourth, your code change to add the additional pre-condition check:

       protected void removeRange(int fromIndex, int toIndex) {
           modCount++;
+         if (fromIndex > toIndex)
+             throw new IndexOutOfBoundsException(

needs to be done _before_ the change to modCount!

And finally, the AbstractList.removeRange change:

+      * @throws NoSuchElementException if {@code (toIndex > size())}

seems to reflect an implementation accident rather than a clear API 
design choice. If the toIndex is out of range then 
IndexOutOfBoundsException is what should be thrown. Otherwise you 
constrain any subtypes that override this to throw an exception type 
that only has meaning with the AbstractList implementation strategy - 
and by doing so you are making ArrayList.removeRange violate this new 
specification.

It is unfortunate that the existing specification(s) for removeRange are 
lacking this key detail on exception processing, and lack consistency 
between AbstractList and it's sublcass ArrayList. I think ArrayList has 
the better/cleaner specification and that should be pushed up 
AbstractList and AbstractList's implementation should be modified to 
explicitly check the pre-conditions.

David
-----

On 14/03/2014 5:42 AM, Ivan Gerasimov wrote:
> Sorry, I forgot to incorporate changes to AbstractList.removeRange()
> documentation, which you Martin had suggested.
>
> Here's the webrev with those included:
> http://cr.openjdk.java.net/~igerasim/8014066/2/webrev/
>
> Sincerely yours,
> Ivan
>
>
> On 13.03.2014 23:03, Ivan Gerasimov wrote:
>> Would you please take a look at the updated webrev:
>> http://cr.openjdk.java.net/~igerasim/8014066/1/webrev/
>>
>> In addition to the javadoc correction, it includes a regression test
>> and a check for (fromIndex > toIndex).
>> The last check turns out to be sufficient for removeRange() method to
>> agree with the javadoc.
>> Other checks are handled by the following System.arraycopy() call.
>>
>> Sincerely yours,
>> Ivan
>>
>>
>> On 13.03.2014 22:27, Ivan Gerasimov wrote:
>>>
>>> On 13.03.2014 22:16, Ivan Gerasimov wrote:
>>>>
>>>> On 13.03.2014 20:37, Martin Buchholz wrote:
>>>>> The corner case for removeRange(SIZE, SIZE) does seem rather
>>>>> tricky, and it's easy for an implementation to get it wrong.  All
>>>>> the more reason to add tests!
>>>>>
>>>> It was a good idea to add a test for removeRange().
>>>> I just discovered that IOOB isn't thrown when you call
>>>> removeRange(1, 0) or removeRange(4, 0).
>>>> However, the exception is thrown when you call removeRange(5, 0).
>>>>
>>>> The fix seems to become a bit more than just a doc typo fix :-)
>>>>
>>>
>>> And when you do list.removeRange(1, 0), the list becomes longer.
>>>
>>>
>>>> Sincerely yours,
>>>> Ivan
>>>>
>>>>>
>>>>> On Thu, Mar 13, 2014 at 9:15 AM, Ivan Gerasimov
>>>>> <ivan.gerasimov at oracle.com <mailto:ivan.gerasimov at oracle.com>> wrote:
>>>>>
>>>>>     Thank you Chris!
>>>>>
>>>>>     It is System.arraycopy() method, where checking is performed and
>>>>>     the exception is thrown.
>>>>>     Here's this code:
>>>>>       if ( (((unsigned int) length + (unsigned int) src_pos) >
>>>>>     (unsigned int) s->length())
>>>>>          || (((unsigned int) length + (unsigned int) dst_pos) >
>>>>>     (unsigned int) d->length()) ) {
>>>>> THROW(vmSymbols::java_lang_ArrayIndexOutOfBoundsException());
>>>>>       }
>>>>>
>>>>>     This confirms that size() is a valid value for fromIndex.
>>>>>
>>>>>     Another way to think of it is that fromIndex <= toIndex, and
>>>>>     toIndex can be equal to size().
>>>>>     Therefore, fromIndex can be equal to size() too.
>>>>>
>>>>>     The documentation also says that 'If toIndex==fromIndex, this
>>>>>     operation has no effect.', so removeRange(size(), size()) is a
>>>>>     valid expression and should not cause an exception be thrown (and
>>>>>     it actually does not).
>>>>>
>>>>>     Sincerely yours,
>>>>>     Ivan
>>>>>
>>>>>
>>>>>     On 13.03.2014 19:47, Chris Hegarty wrote:
>>>>>
>>>>>         Ivan,
>>>>>
>>>>>         This does look a little odd, but since fromIndex is inclusive
>>>>>         I would think that it should throw if passed a value of
>>>>> size() ??
>>>>>
>>>>>         -Chris.
>>>>>
>>>>>         On 13 Mar 2014, at 15:29, Ivan Gerasimov
>>>>>         <ivan.gerasimov at oracle.com <mailto:ivan.gerasimov at oracle.com>>
>>>>>         wrote:
>>>>>
>>>>>             Hello!
>>>>>
>>>>>             Would you please review a simple fix of the javadoc for
>>>>>             ArrayList#removeRange() method?
>>>>>
>>>>>             The doc says that IndexOutOfBoundsException is thrown if
>>>>>             fromIndex or toIndex is out of range (fromIndex < 0 ||
>>>>>             fromIndex >= size() || toIndex > size() || toIndex <
>>>>>             fromIndex).
>>>>>
>>>>>             The condition 'fromIndex >= size()' isn't true and should
>>>>>             be removed from the doc.
>>>>>
>>>>>             For example, the code list.removeRange(size(), size())
>>>>>             does not throw any exception.
>>>>>
>>>>>             BUGURL: https://bugs.openjdk.java.net/browse/JDK-8014066
>>>>>             WEBREV:
>>>>> http://cr.openjdk.java.net/~igerasim/8014066/0/webrev/
>>>>> <http://cr.openjdk.java.net/%7Eigerasim/8014066/0/webrev/>
>>>>>
>>>>>             Sincerely yours,
>>>>>             Ivan
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>