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Why 2 interfaces Comparable and Comparator?

Karthik Guru
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Joined: Mar 06, 2001
Posts: 1209
java.lang.Comparable and
java.lang.Comparator
can anyone explain the difference between the 2 interfaces.
Comparable has a method
compareTo(Object o)
So any class which supports sorting of it's objects w'd probably implement this as well.
Now comparator has a compare(Object o1, Object o2)
Since this is taking 2 objects i don't expect it to be a part of the class which wants to support sorting (itself).
thanks,
karthik.
John Dale
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Joined: Feb 22, 2001
Posts: 399
Your question seems to answer itself. But if it would help to have an example, consider that String impements Comparable, and has a compareTo(Object) method that is case-sensitive, as is its equals() method. However, sometime you need to do case-insensitive comparison of strings. So String provides String.CASE_INSENSITIVE_ORDER, an implementation of Comparitor that provides a case-insensitive compare(Object, Object) method. (Since the case-insensitive comparitor is not consistent String's equals method, you have to be careful about where you use it.)
Dave Van Even
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Joined: Jul 19, 2001
Posts: 101
hi,
I was just (5 minutes ago) studying this
It goes like this: If you are designing your OWN classes and there is a need for comparing, you might prefer to use the natural comparison method by implementing Comparable
here is code I just had to copy from my editor

Getal = dutch for Number (I couldn't use Number as classname could I )
But what if you get a class that you don't have the source code of and you need to sort the items ? Or what if the class has allready implemented Comparable, but you want to sort the class on another value ?
then you might choose for the Comparator method! You just create a new Class and implement the compare() method; Usually the equals method inherited from Object or whatever is just fine
here is an example

The AlphabeticComparator class does actually the same as the public static final Comparator CASE_INSENSITIVE_ORDER from String
Thanks for pointing that out John!! I didn't knew it had that field
anyway, karthik hope I could help you
Dave

[This message has been edited by Dave Van Even (edited October 14, 2001).]
[This message has been edited by Dave Van Even (edited October 14, 2001).]
Dave Van Even
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Joined: Jul 19, 2001
Posts: 101
damn.. half my code gets transformed into garbage be because the UBB code tag doesn't translate to HTML codes
hope you get the idea
 
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