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From "Mark R. Diggory" <>
Subject Re: [Math] Frequency : Is int comparable to Integer through default comparator
Date Thu, 12 Aug 2004 03:17:15 GMT
I do agree Phil, the modified example I provided of a NaturalComparator 
met these same criteria.


Phil Steitz wrote:

>I will fix the bug, as mentioned in my earlier post so that the implementation matches
the javadoc (i.e., Integers, ints, Longs, longs are all treated the same, stored as Long instances
in the TreeMap).  Otherwise, incomparable values will cause runtime exceptions as documented.
 I am -1 to changing the interface or to trying to in general make incomparable objects comparable
(other than the special case above).  Users who are adding incomparable objects to a frequency
distribution are abusing the API, so a runtime exception is appropriate.  A checked exception
is neither appropriate nor desirable in this case, IMHO.  
>The standard use cases for this class will use Strings, Chars or integral types uniformly.
 The requirement that the values be comparable is essential to the API -- without it cumulative
counts / percentages make no sense.  
>	-----Original Message----- 
>	From: Mark R. Diggory [] 
>	Sent: Wed 8/11/2004 4:48 PM 
>	To: Jakarta Commons Users List 
>	Cc: 
>	Subject: Re: [Math] Frequency : Is int comparable to Integer through default comparator
>	Shing Hing Man wrote:
>	>Mark,
>	>  Thank you for explaining the cause of the
>	>IllegalArgumentException !
>	>
>	>I think there is no need to implement  a 'default
>	>comparator'
>	>to make objects of type like Integer and Long
>	>comparable.
>	> 
>	>
>	I t would be a useful addition for users who want that functionality
>	with java.lang.Numbers and Strings etc, I agree it probably doesn't need
>	to be a default. It would make a nice utility for the utils section.
>	>The current version of the class Frequency would meet
>	>the needs
>	>of most user. 
>	>
>	> 
>	>
>	Well, the issue goes deeper than comparision of Integer and Long, the
>	thrown exception is "obtuse", its unclear from the
>	IllegalArgumentException itself why the ClassCastException occurs until
>	you look at both the implementation of Frequency and its underlying
>	TreeMap. As such I think it is not user friendly. We can do better than
>	this.  I agree we can keep the existing expected behavior, but I think
>	the Exception handling should be improved or at least made more
>	descriptive. The issue has to do with the fact that the methods never
>	define the IllegalArgumentException as being "thrown" so user will not
>	get a compilation error if they do not handle it appropriately. In the
>	end the result would be unexpected behavior (no matter how much is
>	documented in the javadoc). The users should be forced to handle the use
>	case by catching the Exception in thier code. This could be either by
>	throwing the IllegalArgumentException (probably a bad choice) or by
>	creating an Exception specifically for this issue and throwing it from
>	our methods.
>	>In most situations, your data could  be casted to a
>	>common type.
>	> 
>	>
>	The risk with Frequency is that the interface "promotes" heterogeneous 
>	and incomparable object usage in the methods that are implemented. For
>	instance:
>	    public void addValue(int v) {
>	        addValue(new Long(v));
>	    }
>	    public void addValue(long v) {
>	        addValue(new Long(v));
>	    }
>	    public void addValue(char v) {
>	        addValue(new Character(v));
>	    }
>	The fact that the user can call addValue(long) or addValue(int) and then
>	call addValue(char) creates a situation where the
>	interface/implementation itself actually promotes the creation of
>	incomparable objects in the tree. If this is going to be maintained then
>	I would argue there should at least be a comparator that handles these
>	cases.
>	>If a user wants to  add data of different types, or
>	>even their
>	>own custom type, he/she could implement their own
>	>comparator to
>	>avoid the ClassCastException, hence the
>	>IllegalArgumentException,
>	>when retrieving elements from TreeMap.
>	> 
>	>
>	I think we can easily improve upon the implementation to manage the contents of the Tree
better. A good Comparator can provide us better functionality, better Exception handling is
important as well.
>	-Mark
>	--
>	Mark R. Diggory
>	Software Developer
>	Harvard MIT Data Center
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Mark R. Diggory
Software Developer
Harvard MIT Data Center

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