map遍历的4种方式

public static void main(String[] args) {  Map<String, String> map = new HashMap<String, String>();  map.put("1", "value1");  map.put("2", "value2");  map.put("3", "value3");      //第1种：普遍使用，二次取值      System.out.println("通过Map.keySet遍历key和value：");      for (String key : map.keySet()) {       System.out.println("key= "+ key + " and value= " + map.get(key));      }      //第2种：通过迭代器      System.out.println("通过Map.entrySet使用iterator遍历key和value：");      Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();      while (it.hasNext()) {       Map.Entry<String, String> entry = it.next();       System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());      }      //第3种：推荐，尤其是容量大时      System.out.println("通过Map.entrySet遍历key和value");      for (Map.Entry<String, String> entry : map.entrySet()) {       System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());      }      //第4种：只能取出值      System.out.println("通过Map.values()遍历所有的value，但不能遍历key");      for (String v : map.values()) {       System.out.println("value= " + v);      } }