package Map;  import java.util.*;  public class HashMaps {   public static void main(String[] args) {     Map map = new HashMap();     map.put("a", "aaa");     map.put("b", "bbb");     map.put("c", "ccc");     map.put("d", "ddd");      Iterator iterator = map.keySet().iterator();     while (iterator.hasNext()) {       Object key = iterator.next();       System.out.println("map.get(key) is :" + map.get(key));     }      Hashtable tab = new Hashtable();     tab.put("a", "aaa");     tab.put("b", "bbb");     tab.put("c", "ccc");     tab.put("d", "ddd");     Iterator iterator_1 = tab.keySet().iterator();     while (iterator_1.hasNext()) {       Object key = iterator_1.next();       System.out.println("tab.get(key) is :" + tab.get(key));     }      TreeMap tmp = new TreeMap();     tmp.put("a", "aaa");     tmp.put("b", "bbb");     tmp.put("c", "ccc");     tmp.put("d", "ddd");     tmp.put("a", "aba");     Iterator iterator_2 = tmp.keySet().iterator();     while (iterator_2.hasNext()) {       Object key = iterator_2.next();       System.out.println("tmp.get(key) is :" + tmp.get(key));     }               LinkedHashMap<String ,Integer> linkedHashMap = new LinkedHashMap<String,Integer>();     linkedHashMap.put("dasdsa", 1);     linkedHashMap.put("gdsf",2);     linkedHashMap.put("texvdfd", 3);     linkedHashMap.put("bdada", 4);          linkedHashMap.put("gdsf",3);     for(String temp : linkedHashMap.keySet()){       System.out.println(temp);     }        }  }