How to iterate complicated List of Maps containing Maps

Question

I'm having problems working out how to iterate this structure.

ArrayList<HashMap<String, HashMap<String, String>>> list

Can you help me work out how to walk the complete structure?

Here's what I've got to so far but where do I go next? I need to get all the way down to the deepest data.

for (HashMap<String, String> map : data)
     for (Entry<String, String> entry : map.entrySet())

Does it have to be an `ArrayList`? `LinkedList` is more efficient for iterating. — Dragondraikk, Jul 21 '15 at 13:01
access for what, it depends what/how the data will be used/accessed, also what have you tried so far — depperm, Jul 21 '15 at 13:02
@Dragondraikk i just want to read all the data.it could be linkedlist also. — Spartan, Jul 21 '15 at 13:03
possible duplicate of [Performance: Iterating through a List in Java](http://stackoverflow.com/questions/2642004/performance-iterating-through-a-list-in-java) — Shekhar Khairnar, Jul 21 '15 at 13:04
Well with the updated description this question just displays a lack of research. `List.iterator()` and loops are not particularly difficult to google for. — Dragondraikk, Jul 21 '15 at 13:05
use list iterator or a for loop or a while loop...all these are normal and efficient ways !! — Renjith, Jul 21 '15 at 13:06

OldCurmudgeon · Accepted Answer · 2015-07-21T13:24:01.333

How about this?

    ArrayList<HashMap<String, HashMap<String, String>>> list = new ArrayList<>();

    for (HashMap<String, HashMap<String, String>> m : list) {
        for (Map.Entry<String, HashMap<String, String>> e : m.entrySet()) {
            String key1 = e.getKey();
            for (Map.Entry<String, String> me : e.getValue().entrySet()) {
                String key2 = me.getKey();
                String value = me.getValue();
            }
        }
    }

Note that you really should be using the interface form of the objects:

    List<Map<String, Map<String, String>>> list = new ArrayList<>();

    for (Map<String, Map<String, String>> m : list) {
        // All Maps.
        for (Map.Entry<String, Map<String, String>> e : m.entrySet()) {
            // Outer key.
            String key1 = e.getKey();
            for (Map.Entry<String, String> me : e.getValue().entrySet()) {
                // Inner key.
                String key2 = me.getKey();
                // The String value.
                String value = me.getValue();
            }
        }
    }

How to iterate complicated List of Maps containing Maps

1 Answers1