TreeSet

import java.util.*;

// Declare the variable using the interface of the object for flexibility.
// Non-primative data types only.
Set<String> movies = new TreeSet<String>();

movies.add(E);
// TreeSet will be sorted by element.
// Work with any comparable object.

movies.add("The Shining");
movies.add("Dawn of the Dead");
movies.add("Zombieland");

// extrait de la classe TreeSet
public class TreeSet extends AbstractSet
        implements SortedSet, Cloneable, java.io.Serializable {
  //...
  public TreeSet() {
    this(new TreeMap());
  }
  //...
}

// par défaut
TreeSet ensemble = new TreeSet();
// comparateur
Comparator comparateur = new Comparateur();
TreeSet ensemble = new TreeSet(comparateur);

// classe Comparateur implémentant l'interface Comparator
public class Comparateur implements Comparator {
  public int compare(Object obj1, Object obj2){
    return ((Comparable)obj2).compareTo(obj1);
  }
  public boolean equals(Object obj){
    return this.equals(obj);
  }
}

TreeSet: Can contain only unique values and it is sorted in ascending order
TreeMap: Can contain only unique keys and keys are sorted in ascending order.