public static void main(String[] args) {
           Map
    
      map = new HashMap
     
      ();         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
      
       
        > it = map.entrySet().iterator();         while (it.hasNext()) {
           Map.Entry
        
          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
         
           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); } }