Map.Entry Details help

[kalpana Kumar]

Hi all,
I would like to know the advantages of using Map.Entry it is used to get the Set view of the map. But I need much more details regarding the same.
I saw an example in which there is a HashMap and since Iterator cannot be used on HaspMap it is converted into Set using entrySet
h_map.entrySet().iterator();
While Iterating, (Map.Entry)iter.next() is used. I would like to know why is that necessary.
Why not a Map be used to get the KeyValue pair. I not getting in the Order in which the values were added into the HashMap too, if I consider that to be the advantage of using Map.entry.

Please help needed.

Thanks

[David Harkness]

First, HashMap allows you to iterate the keys, the values, or the key/value pairs. Map.entrySet().iterator() is for iterating key/value pairs stored in Map.Entry objects.

HashMap map = ...;
for ( Iterator i = map.entrySet().iterator() ; i.hasNext() ; )
{
    Map.Entry entry = (Map.Entry) i.next();
    System.out.println(entry.getKey() + " --> " + entry.getValue());
}

The reason to use this method is so you don't have to look up the value for each key when iterating keys.

If you need the keys and key/values in the same order as you added them, you'll need to use JDK 1.4's LinkedHashMap class or roll your own.