Map an instance containing a list to a flatMap (using stream)

user8166384 :

i have the following class 'Store':

public class Store {
    private String storeId;
    private String storeName;
    private List<DayOfWeek> openiningDays;
}

(e.g.:)
{
    storeId: 1
    storeName: blabla
    openingDays: [MONDAY,TUESDAY,...]
}

and a list of 'x' Stores

List<Store> stores = ......

Using the stream class of java, or anther kind method, i want to get a flat list of weekdays, including the storeName and storeId.

e.g: (desired result)

[
    {
    storeId: 1
    storeName: blabla
    openingDay: MONDAY
    },
    {
    storeId: 2
    storeName: blabla
    openingDay: SATURDAY
    },
    {
    storeId: 3
    storeName: blabla
    openingDay: FRIDAY
    }
]

I´ve already found a possible solution, but i´m not satisfied with it:

List<OtherType> transformed = new List<>();
for (Store store : stores) {
    for (DayOfWeek currentDay : openingDays) {
        transformed.add(new OtherType(.....));
    }
}

Is there any possibility to do this with something like 'flatMap(..)' (to be able to use the stream class of java) or another predefined method?

Thank you in advance :)

Deadpool :

By using flatMap you can achieve this, First stream the stores list and then in flatMap stream List<DayOfWeek> by mapping each DayOfWeek to OtherType.

//Assuming you have constructor in OtherType with three arguments like OtherType(String storeId, String storeName, DayOfWeek day)

List<OtherType> transformed = stores.stream()
                                    .flatMap(store->store.getOpeningDays().stream()
                                                                      .map(day->new OtherType(store.getStoreId(),store.getStoreName(),day)))
                                    .collect(Collectors.toList());