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")); } }