Map遍历的四种方法

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");    //第一种：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));  }    //第二种  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());  }    //第三种：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());  }  //第四种  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);  } }