Collections.

[Dave Johnson]

Hi all.
Here is the code:

 
import java.util.*;
public class FindDups {
public static void main(String args[]) {
Set s = new TreeSet();
for (int i=0; i<args.length; i++)
if (!s.add(args[i]))// I don't quite follow this!!!
System.out.println("Duplicate detected: "+args[i]);

System.out.println(s.size()+" distinct words detected: "+s);
}
}

Found this code on this link java.sun. What I would like explaining is the logic in the if statement I have commented. I am not that familier with all the different collection interfaces & classes.
Thanks, Dave.

[Mika Leino]

The TreeSet's add method returns true if the addition was succesful. As the TreeSet, like all Sets, doesn't allow duplicates it will return false when trying to add a String that already exists in the Set.
Don't know if this helps, but another way to present this would be like this:

import java.util.*;
public class FindDups {
    public static void main(String args[]) {
        Set s = new TreeSet();
        for (int i=0; i<args.length; i++) {
            boolean b = s.add(args[i]); // Try to add the String to the Set
            if (!b) {                   // Test whether the addition was succesful or not
                System.out.println("Duplicate detected: "+args[i]);
            }
        }
        System.out.println(s.size()+" distinct words detected: "+s);
    }
}

[Dave Johnson]

Thanks Mika, I can see the logic clearly now, your'a'good'un!

[Steve Lovelace]

TreeSet implements Set which defines add(), addAll(), remove(), removeAll() and retainAll(), all of which return boolean. Each of these adds or removes objects to/from the set. But adding/removing may turn out to be a no-op (because the specified object is/is-not in the set). So each of these methods returns a boolean which says "I changed the set".