In java, and there is one catch here. The objects are already compiled and the hash() and equals() methods therefore cannot be over written. Throwing it into a set, then back into a list will not work because the criteria for uniqueness isn't currently defined in equals() and this cannot be overridden.
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What is your criteria for 'uniqueness' which is not defined in the equals() method?Atreys– Atreys2011-09-21 15:33:18 +00:00Commented Sep 21, 2011 at 15:33
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3 Answers
You should still be able to create subclasses and create equals and hashcode methods that work, unless the classes/methods are final.
If that is the case, you could use composition, basically create a wrapper for the things you are putting in the collection, and have the wrapper's equals and hashcode implement the contract correctly, for the thing being wrapped.
You are in a tough position, because what I am reading is that the original classes are not following the contract for equals and hashcode which is a real problem in Java. It's a pretty serious bug.
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Dilum Ranatunga
The point being that if comparison is cheaper, the TreeSet approach may be better. the original question did not say anything about having a good hashcode.
Dilum Ranatunga
If you have a good hashcode as well, you can also use containment; i.e. use a wrapper rather than a subclass.
Write a custom Comparator for your objects and use Collections.sort() to sort your list. And then remove duplicates by going though a list in a loop.
answered Sep 21, 2011 at 15:02
Andrey Adamovich
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Dilum Ranatunga
... or use the
Comparator with a TreeSeta compareTo method would return -1, 0, 1; if 0, remove from list.
