Maps differ from lists and sets in that they are ordered collections of key-value pairs. : Map « Utility Classes « SCJP

1. SCJP
2. Utility Classes
3. Map

The TreeMap class implements a sorted binary tree.

import java.util.Collection;
import java.util.Iterator;
import java.util.TreeMap;

public class MainClass {
  public static void main(String args[]) {
    TreeMap map = new TreeMap();
    map.put("one", "1");
    map.put("two", "2");
    map.put("three", "3");
    map.put("four", "4");
    map.put("five", "5");
    map.put("six", "6");
    displayMap(map);
  }

  static void displayMap(TreeMap map) {
    System.out.println("The size of the map is: " + map.size());
    Collection c = map.entrySet();
    Iterator i = c.iterator();
    while (i.hasNext()) {
      Object o = i.next();
      if (o == null)
        System.out.println("null");
      else
        System.out.println(o.toString());
    }
  }
}

The size of the map is: 6
five=5
four=4
one=1
six=6
three=3
two=2