Get Set view of Keys from TreeMap in Java

/*from   ww w  .  j av a  2s.c o m*/
import java.util.Iterator;
import java.util.TreeMap;
import java.util.Set;
public class Main {
  public static void main(String[] args) {
    TreeMap<String, String> treeMap = new TreeMap<String, String>();
    treeMap.put("1", "One");
    treeMap.put("3", "Three");
    treeMap.put("2", "Two");

    Set st = treeMap.keySet();
    Iterator itr = st.iterator();
    while (itr.hasNext()){
      System.out.println(itr.next());
    }
    st.remove("1");

    System.out.println(treeMap.containsKey("1"));
  }
}