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From "Phil Steitz" <p...@steitz.com>
Subject RE: [Math] Frequency : Is int comparable to Integer through default comparator
Date Thu, 12 Aug 2004 02:29:14 GMT
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.  
 
Phil

	-----Original Message----- 
	From: Mark R. Diggory [mailto:mdiggory@latte.harvard.edu] 
	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
	http://www.hmdc.harvard.edu
	
	
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