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From Spark Shen <smallsmallor...@gmail.com>
Subject Re: [classlib][luni] Is fully comply with Comparator.compare(T, T) necessary (Re JIRA harmony 1026)
Date Wed, 02 Aug 2006 07:21:03 GMT
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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