Java NavigableMap get floor key

import java.util.NavigableMap;
import java.util.TreeMap;

public class Main {
  public static void main(String args[]) {

    NavigableMap<String, Integer> nav = new TreeMap<String, Integer>();
    nav.put("1", 1);
    nav.put("2", 2);
    nav.put("3", 3);
    nav.put("4", 4);
    nav.put("5", 5);
    /*from w  ww  .ja  v  a 2 s.  c o m*/
    System.out.println(nav);
    
    System.out.println(nav.floorKey("3"));
    
    System.out.println(nav.floorKey("Not Exist"));
  }
}