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 <[EMAIL PROTECTED]>:
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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