      1  import java.util.Set;

      2  import java.util.TreeSet;

      3

      4  /**

      5     This program tests a tree set with a class that implements the Comparable interface.

      6  */

      7  public class TreeSetDemo

      8  {

      9     public static void main(String[] args)

     10     {

     11        Country country1 = new Country("Uruguay", 176220);

     12        Country country2 = new Country("Thailand", 514000);

     13        Country country3 = new Country("Belgium", 30510);

     14

     15        Set<Country> countries = new TreeSet<Country>();

     16

     17        countries.add(country1);

     18        countries.add(country2);

     19        countries.add(country3);

     20        countries.add(country1); // Has no effect

     21        countries.remove(country3);

     22        countries.remove(country3); // Has no effect

     23        countries.add(country3);

     24

     25        System.out.println(countries);

     26     }

     27  }