Re: problem with Sets

Robert Klemme <>
Thu, 21 Sep 2006 12:12:34 +0200
On 21.09.2006 11:56, bassel wrote:

greeting everyone,

I have a problem with sets, according to the API documentation

Class TreeSet<E>
public boolean add(E e)

    Adds the specified element to this set if it is not already
present. More formally, adds the specified element e to this set if the
set contains no element e2 such that (e==null ? e2==null :
e.equals(e2)). If this set already contains the element, the call
leaves the set unchanged and returns false.

new I have this code:
Set identities = new java.util.TreeSet<Identity>();

output is:

where's the problem???

You probably did not implement class Identity properly. You need to
implement compareTo() for a TreeSet. For a HashSet you need equals()
and hash(). You probably should do all of these methods for
completeness reasons.

Kind regards


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