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An implementation of a SortedSet is the TreeSet class, which uses a tree as its implementation:

Object
    AbstractCollection (implements Collection)
        AbstractSet (implements Set)
            TreeSet (implements SortedSet)

package examples;

import java.util.Iterator;
import java.util.TreeSet;

public class TreeSetExample
{
  public static void main(String[] args)
  {
    TreeSet set = new TreeSet();
    set.add("Mary");
    set.add("Frank");
    set.add("Joe");
    set.add("Sylvia");
    set.add("Vanessa");
    set.add("Frank");   // Duplicate

    for (Iterator iter = set.iterator(); iter.hasNext(); )
    {
      String name = (String) iter.next(); // Note required cast
      System.out.println(name);
    }
  }
}

Note the minimal changes to the program from the earlier HashSet example.   This is a consequence of the consistent use of interfaces, and having different implementations that use the same interface.

Here's the output of the example:

Frank
Joe
Mary
Sylvia
Vanessa

which shows that we still have no duplicates, but that the elements are now returned in the proper order (in this case, alphabetically).

This page was last modified on 02 October, 2007