Iteration of HashMap<> included in List<> to get addition of array variables included in map as values in java

Question

I have BankDetails as pojo object with following variables and its getters and setters.

private String bankName;
private  Map<String,Long[]>  monthMap= newHashMap<String,Long[]>();
private String month;

now I have created List with each bean of BankDetails stored in list with multiple keys and values in its map eg

for one bean I have

map1 = 05, [8,0,0] ;map2 = 06, [6,0,4] ;map3 = 07, [45,3,0] ;map4 = 08, [0,56,9] ;

for second bean I have

map1 = 05, [0,0,0] ;map2 = 06, [8,0,4] ;map3 = 07, [5,0,1] ;map4 = 08, [2,6,8] ;

...

Where 05,06,07 and 08 are months.

now I want to have sum of all map1s map2s map3s and map4s from all beans vertically.

now, what I want is to have grandTotal monthly of array elements, of all List objects and return List which will have only 4 objects having total of all four as shown below.

map1- 05, [8, 0 ,0] ; map2- 06, [12,0,8] ; map3- 07,[50,3,1] : map4- 08, [2,62,17]

please suggest how can I do it. Being newBee in java really weak in iterations and logic.

Answer 1

You can do something like this:

    // Declare a ArrayList of Map Objects
    ArrayList<Map<String,Long[]>> mapsList = new ArrayList<>();

    // add all the beans
    mapsList.add(monthMap);
    mapsList.add(monthMap2);
    .
    .


    // declare a map for storing the sum
    Map<String,Long[]> sumMap = new HashMap<>();

    // for every key in map (assuming maps have the same amount 
    // of key-value pairs)
    for(String str : mapsList.get(0).keySet()){
        // initialising sum for long arrays
        Long[] sum = {0L,0L,0L};
        // for every map bean
        for (int i = 0; i < mapsList.size(); i++){
            // for every column in long array of map
            for (int j = 0; j < mapsList.get(i).get(str).length; j++) {
                sum[j] += mapsList.get(i).get(str)[j];
            }
        }
        sumMap.put(str,sum);
    }

I hope that helped.