JAVA how to iterate over values in a map of a map

Question

i have map of map i created with

Map<String, Map<String, String>> doubleMap = new HashMap<>();

and i try iterating over values of keys in second map.

so it can be like:

Key1 -> KeyA -> value1

|--------> KeyB -> value2

|--------> KeyC ->value3

Key2 -> KeyA -> value2

|--------> KeyB -> value4

|--------> KeyC -> value1

continuing on for long as i want.

i want to check if there is value in map that matches an other string.

so i have mainValue = "value2" and i try loop over all values in doubleMap with value variable called thisValue and increment counter if thisValue.equals(mainValue)

i dont know how i get thisValue . i try like this

thisValue = doubleMap.get(currentNumKey).keySet().toArray()[counter]

but that give me letterKeys.

if i do thisValue = doubleMap.get(currentNumKey).get(currentLetterKey) it give me the right value i want, but i not can iterate over all values

thanks you

Answer 1

Map<String, Map<String, String>> nestedMap = new HashMap<>();
nestedMap.put ... 

Renamed (doubleMap is very misleading), and indicated that creating an empty alone map wont do.

Now you can iterate your maps like:

for (Entry<Map<Map<String, String>>> outer : nestedMap.entrySet) {
  outer.getKey() ... would be "Key1"
  outer.getValue() ... represents that inner map

And for the inner loop, it is very much the same; meaning that you can use for-each and entrySet() on the value returned by outer.getValue().

Answer 2

You can obtain a Collection of all the values in a map using the values() method. For doubleMap , that will give you a collection of Map<String,String> . You can then iterate over that collection and for each Map , do the same trick to find your value:

for (Map<String,String> map : doubleMap.values()) {
    for (String val : map.values()) {
        if (mainValue.equals(val)) {
            // value was found
        }
    }
}

If you need the keys that lead to that value (which, of course, may occur more than once), then you'll need to iterate over the key set, obtained using Map.keySet() (or entry set, obtained using Map.entrySet() ) for doubleMap and also for each Map retrieved for each key. The loops should look similar.