Bugs in Frequency API
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Key: MATH-259
URL: https://issues.apache.org/jira/browse/MATH-259
Project: Commons Math
Issue Type: Bug
Reporter: Sebb
I think the existing Frequency API has some bugs in it.
The addValue(Object v) method allows one to add a plain Object, but one cannot
add anything further to the instance, as the second add fails with
IllegalArgumentException.
In fact, the problem is with the first call to addValue(Object) which should
not allow a plain Object to be added - it should only allow Comparable objects.
This could be fixed by checking that the object is Comparable.
Similar considerations apply to the getCumFreq(Object) and getCumPct(Object)
methods - they will only work with objects that implement Comparable.
The getCount(Object) and getPct(Object) methods don't fail when given a
non-Comparable object (because the class cast exception is caught), however
they just return 0 as if the object was not present:
{code}
final Object OBJ = new Object();
f.addValue(OBJ); // This ought to fail, but doesn't, causing the
unexpected behaviour below
System.out.println(f.getCount(OBJ)); // 0
System.out.println(f.getPct(OBJ)); // 0.0
{code}
Rather than adding extra checks for Comparable, it seems to me that the API
would be much improved by using Comparable instead of Object.
Also, it should make it easier to implement generics.
However, this would cause compilation failures for some programs that pass
Object rather than Comparable to the class.
These would need recoding, but I think they would continue to run OK against
the new API.
It would also affect the run-time behaviour slightly, as the first attempt to
add a non-Comparable object would fail, rather than the second add of a
possibly valid object.
But is that a viable program? It can only add one object, and any attempt to
get statistics will either return 0 or an Exception, and applying the
instanceof fix would also cause it to fail.
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