1  import java.util.*;
  2  
  3  public class TestTreeSet {
  4    public static void main(String[] args) {
  5      // Create a hash set
  6      Set<String> set = new HashSet<>();
  7  
  8      // Add strings to the set
  9      set.add("London");
 10      set.add("Paris");
 11      set.add("New York");
 12      set.add("San Francisco");
 13      set.add("Beijing");
 14      set.add("New York");
 15  
 16      TreeSet<String> treeSet = new TreeSet<>(set);
 17      System.out.println("Sorted tree set: " + treeSet);
 18  
 19      // Use the methods in SortedSet interface
 20      System.out.println("first(): " + treeSet.first());
 21      System.out.println("last(): " + treeSet.last());
 22      System.out.println("headSet(\"New York\"): " + 
 23        treeSet.headSet("New York"));
 24      System.out.println("tailSet(\"New York\"): " + 
 25        treeSet.tailSet("New York"));
 26  
 27      // Use the methods in NavigableSet interface
 28      System.out.println("lower(\"P\"): " + treeSet.lower("P"));
 29      System.out.println("higher(\"P\"): " + treeSet.higher("P"));
 30      System.out.println("floor(\"P\"): " + treeSet.floor("P"));
 31      System.out.println("ceiling(\"P\"): " + treeSet.ceiling("P"));
 32      System.out.println("pollFirst(): " + treeSet.pollFirst());
 33      System.out.println("pollLast(): " + treeSet.pollLast());
 34      System.out.println("New tree set: " + treeSet);
 35    }
 36  }