Map 的遍历方法

  Map<String, String> map = new HashMap<String, String>();  
  map.put("key1", "value1");  
  map.put("key2", "value2");  
  map.put("key3", "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</span>  
  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);  
  }