How to get the elements in correct order from iterator()

Question

Here is my code to store the data into HashMap and display the data using iterator

public static void main(String args[]) {
    HashMap<String, String> hm = new HashMap<String, String>();
    hm.put("aaa", "111");
    hm.put("bbb", "222");
    hm.put("ccc", "333");
    hm.put("ddd", "444");
    hm.put("eee", "555");
    hm.put("fff", "666");

    Iterator iterator = hm.keySet().iterator();

    while (iterator.hasNext()) {
        String key = (String) iterator.next();
        String val = hm.get(key);

        System.out.println(key + " " + val);
    }
}

But it is not displaying in the order in which I stored. Could someone please tell me where am I going wrong? How can I get the elements in the order?

Answer 1

A HashMap has no guaranteed order:

This class makes no guarantees as to the order of the map;

Use a LinkedHashMap.

Hash table and linked list implementation of the Map interface, with predictable iteration order.

Answer 2

You need to use a LinkedHashMap because it maintains ordering of its entries, unlike HashMap.

From the javadocs:

... implementation of the Map interface with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order).