Question

I have a HashMap, which contains another HashMap. I want to iterate over the first HashMap and use the Key values from that. Then, as I iterate over the first HashMap I want to start an inner loop iterating over the second HashMap, getting all the values.

The problem I have so far is that I can’t figure out how to get the keys from the Iterator.

HashMap<String, HashMap<Integer, String>> subitems = myHashMap.get("mainitem1");

Collection c = subitems.values();
Iterator itr = c.iterator();

while(itr.hasNext())
{
    // Get key somehow? itr.getKey() ???

    // contains the sub items
    HashMap productitem = (HashMap)itr.next();
}

The data that i get from subitems is this:

{Item1{0=sub1, 1=sub2}, Item2{0=sub3, 1=sub4}}

Then, in the while loop productitem contains the ‘sub items’. But i can’t find out where i can get the key value ‘Item1’ and ‘Item2’ from.

How can i get those?

Answer 1

You can’t get the key from values().iterator().

You need to use entrySet().iterator(). That will return Map.Entry<K,V> objects on which you can call getKey() and getValue().

for (Map.Entry<Integer,Key> entry : subitems.keySet()) {
  Integer key = entry.getKey();
  String value = entry.getValue();

  // do stuff
}

I’d also like to add that having deeply nested maps of lists of maps is usually a sign that you really want to write custom classes to hold your data. Especially when the maps have pre-defined keys to be used and interpretation of the values in the lists depends on the position within the list! I call this code smell “object denial”.