Question

I want to get all the objects from the list and put them into a Map grouped by creation date, which means the map is like this: Map<String, List<MyObject>>. The MyObject object has a field that stores its creation date.

I’ve thought of doing a nested while loop that looks like this:

public Map<String, List<Expense>> getExpensesSorted(SortType type){
    Map<String, List<Expense>> map = new HashMap<String, List<Expense>>();

    List<Expense> expenses = getAllExpenses(budgetId).getExpenses()
            .getList();

    if (type.equals(SortType.DAY)) {
        Iterator<Expense> expIter = expenses.iterator();

        while (expIter.hasNext()) {
            List<Expense> list = new ArrayList<Expense>();
            Expense exp = (Expense) expIter.next();
            list.add(exp);

            String day = exp.getDate().format("YYYY-MM-DD");
            expIter.remove();

            while (expIter.hasNext()) {
                Expense exp2 = (Expense) expIter.next();
                if (exp2.getDate().format("YYYY-MM-DD").equals(day)) {
                    list.add(exp2);
                    expIter.remove();
                }
            }
            map.put(day, expenses);
        }

    } else if (type.equals(SortType.WEEK)) {
        ...
    } else if (type.equals(SortType.TYPE)) {
        ...
    } else if (type.equals(SortType.CATEGORY)) {
        ...
    }
    return map;
}

But this is wrong, it only gets all the ones that have the same day as the first element, so my map ends up having only one element.

I seriously don’t know how to solve this…

Thanks in advance for any help.

Answer 1

Something like this should do the job. I didn’t compile it though.

while (iter.hasNext()) {
    MyObject obj = (MyObject) iter.next();
    String day = obj.getDate().format("YYYY-MM-DD");

    if(!map.containsKey(day)) {
       map.put(day, new ArrayList<MyObject>());
    }
    List<MyObject> list = map.get(day);
    list.add(obj);
    map.put(day, list);
}