Java HashMap: How to get a key and value by index?

Question

I am trying to use a HashMap to map a unique string to a string ArrayList like this:

HashMap>

Basical

Answer 1

HashMaps are not ordered, unless you use a LinkedHashMap or SortedMap. In this case, you may want a LinkedHashMap. This will iterate in order of insertion (or in order of last access if you prefer). In this case, it would be

int index = 0;
for ( Map.Entry> e : myHashMap.iterator().entrySet() ) {
    String key = e.getKey();
    ArrayList val = e.getValue();
    index++;
}

There is no direct get(index) in a map because it is an unordered list of key/value pairs. LinkedHashMap is a special case that keeps the order.