Creating a TreeSet : TreeSet « Collections « Java Tutorial

1. Java Tutorial
2. Collections
3. TreeSet

The first two constructors create empty tree sets:

public TreeSet()
public TreeSet(Comparator comp)

Pass along a custom Comparator to the constructor that will be used to keep elements ordered.

Once the TreeSet is created, you cannot change the comparator.

import java.util.Collections;
import java.util.Set;
import java.util.TreeSet;

public class MainClass {
  public static void main(String args[]) throws Exception {
    String elements[] = { "A", "C", "D", "G", "F" };
    Set set = new TreeSet(Collections.reverseOrder());
    for (int i = 0, n = elements.length; i < n; i++) {
      set.add(elements[i]);
    }
    System.out.println(set);
    System.out.println(((TreeSet) set).comparator());
  }
}

[G, F, D, C, A]
java.util.Collections$ReverseComparator@192d342