In the loop there is if clause. It checks whether or not Object was added to
unique set. if it is already there the Object is being added to dups set.
Therefore all objects that have several copies are gathered to dups set.
Than those are removed from unique set. Finally we have two separate sets
one of which contains Objects that are presented only once in name[] array
and another which contains Objects that were defined more than once in
name[] array.
On Sat, Dec 18, 2010 at 8:38 PM, Michèle Garoche <migat...@gmail.com> wrote:
>
>
> On Dec 18, 1:44 pm, DHARMENDRAN GOVIND <dharmendr...@gmail.com> wrote:
> > Hello,
> >
> > The below program has declared 2 variables of type Hashset and one of the
> > statements is trying to load duplicate names into variable dup.
> >
> > Question: Doesn't add method of Set interface follow "no duplicate rule"?
> > Then what is the point of having statement uniques.removeAll(dup); Please
> > advice.
> Actually this code does much more than you have observed.
> >
> > package sethashsetfinddup2;
> >
> > import java.util.HashSet;
> > import java.util.Set;
> >
> > public class Main {
> >
> > public static void main(String[] args) {
> >
> > // Set up test data
> > String name[] = {
> > new String("Sang"),
> > new String("Shin"),
> > new String("Boston"),
> > new String("Shin")
> > };
> >
> > Set uniques = new HashSet();
> > Set dups = new HashSet();
> >
> > for (int i=0; i<name.length; i++)
> > if (!uniques.add(name[i]))
> See the add method of HashSet:
> http://download.oracle.com/javase/6/docs/api/java/util/HashSet.html#add(E)
> It returns a boolean that indicates if the element is already
> contained in the HashSet or not.
> Hence this method does two things:
> first it adds the name to uniques, following the non duplicate rules,
> that is it adds only once the "Shin" string.
> Then combined with the following one:
> > dups.add(name[i]);
> it adds to dups the second string "Shin" (not necessary in this order)
> to dups.
> Hence you end up with uniques containing:
> Sang, Shin, Boston
> and dups containing:
> Shin
> >
> > // Remove items that duplicates
> > uniques.removeAll(dups);
> And here, the code remove from uniques all the strings containing in
> dups, that is it removes from uniques the Shin string; and you end up
> with uniques containing:
> Sang, Boston
> >
> That is, exactly what the Unique words says:
>
> > System.out.println("Unique words: " + uniques);
> And what the Duplicate words says:
> > System.out.println("Duplicate words: " + dups);
> > }
> >
> > }
> >
> > Regards
> > Dharmendran
>
> Just put a System.out.println just after the for loop to print uniques
> and dups or run the code step by step with the debugger, it helps
> understand what happens.
>
>
> Michèle Garoche
>
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