Hashmap遍历的几种方式

//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);
 }
}