Hi Spark,

> When both are null, -1 will be returned. This mocked comparator is used
> as a boundary test condition, and under this condition,
> if there is null entry contained in tree map, is will not be included in
> the SortedMap returned by headMap(null) method.

IMHO you need to be carefull here since if o1==null and o2==null then
both compare(o1,o2) and compare(o2,o1) will return -1. And the size of
SortedMap depends on actual execution order of the comparison
operators.

SortedMap headMap(K key) {
...
    K curKey = ...;
    if (comparator.compare(curKey, key) < 0) {
        // true if key == null && curKey == null
        result.put(curKey,...)
    }
...
   return result;
}

Regards,

2006/8/2, Spark Shen <smallsmallorgan@gmail.com>:
> Richard Liang 写道:
> >
> >
> > Spark Shen wrote:
> >> I constructed a MockComparator as below:
> >> public static class MockComparator<T> implements Comparator<T> {
> >> public int compare(T o1, T o2) {
> >> if(null == o1) return -1;
> >> if(o1.equals(o2)) {
> >> return 0;
> >> }
> >> return 1;
> >> }
> >> }
> >>
> >> This comparator regards null as the smallest object and TreeMap uses
> >> this Comparator as a null-tolerable comparator.
> >> And this comparator is used to test the behavior of TreeMap.headMap()
> >> when the input is null.
> >>
> >> Since null is recognized as smallest, the expected length of the
> >> returned SortedMap of TreeMap.headMap(null) will be zero.
> >>
> >> My point here is that, under this situation, the MockComparator does
> >> not care about the order of non-null objects, it just know
> >> null is always smaller. So, is it acceptable that - in this
> >> comparator, compare method does not judge the order of all the
> >> non-null objects?
> >> (does not comply with doc of comparator.compare)
> >>
> > What will happen when both o1 and o2 are null?
> When both are null, -1 will be returned. This mocked comparator is used
> as a boundary test condition, and under this condition,
> if there is null entry contained in tree map, is will not be included in
> the SortedMap returned by headMap(null) method.
>
> Best regards,
>
> >
> > My understanding about mocked objects is that: we could only implement
> > some necessary logic, but the logic must be compliant with the
> > specification. Correct me if I'm wrong. Thanks a lot.
> >
> > Best regards,
> > Richard
> >> Best regards
> >>
> >
>
>
> --
> Spark Shen
> China Software Development Lab, IBM
>
>
>
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>


-- 
Alexei Zakharov,
Intel Middleware Product Division

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