Re: problem with Sets

From:
"Chris Brat" <chrisBrat@gmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
21 Sep 2006 03:29:36 -0700
Message-ID:
<1158834575.860536.296670@k70g2000cwa.googlegroups.com>
Hi,

Heres and example I did - the results are :
true
true
false
[A$Identity@1cdeff]

To be of any actual use you have to correct the compare and equals
methods.

Regards,
Chris

public class A {

    private static class IdentityComparator implements Comparator{
        public int compare(Object a, Object b){
            // implement this correctly
            return 0; // as a test this always indicates equality
        }
    }

    private static class Identity {

        public boolean equals(Object obj){

            // implement this correctly
            return true; // as a test this always indicates equality
        }
    }

    public static void main(String[] args){
        Set identities = new java.util.TreeSet<Identity>(new
IdentityComparator());

        Identity id1 = new Identity();
        Identity id2 = new Identity();

        System.out.println(id1.equals(id2));
        System.out.println(identities.add(id1));
        System.out.println(identities.add(id2));

        System.out.println(identities);
    }
}

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>();
System.out.println(id1.equals(id2));
System.out.println(identities.add(id1));
System.out.println(identities.add(id2));

output is:
------------
true
true
true

where's the problem???

regards,
Bassel

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