Java Collection How to - Merge duplicates and sort with TreeSet

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Question

We would like to know how to merge duplicates and sort with TreeSet.

Answer

import java.util.ArrayList;
import java.util.Collections;
import java.util.TreeSet;
import java.util.List;
import java.util.Set;
/*ww w .j  a  v  a 2s.  c  om*/
public class Main {

    public static TreeSet copySet(List ls) {
        TreeSet s = new TreeSet();
        s.addAll(ls);
        return s;
    }

    public static void main(String[] args) {
        List ls = new ArrayList();
        ls.add(1);
        ls.add(1);
        ls.add(2);
        ls.add(5);
        ls.add(4);
        ls.add(4);

        TreeSet s1 = copySet(ls);
        System.out.println(ls);
        System.out.println(s1);

    }

}

The code above generates the following result.

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