How to do multiple map operations with the same value using Java stream?

January 11, 2022

I have a "root" list which contains objects with different lists inside. I have it now divided in 3 operations but i think it could be done using only one so i wouldn’t repeat code. Is it possible?

List<Prices[]> pricesList = new ArrayList<Prices>();
List<Instructions[]> instructionsList = new ArrayList<Instructions>();
List<Sizes[]> sizesList = new ArrayList<Sizes>();

/* storesList contains a list of Stores which each of them has 
   inside a list of prices, instructions and sizes. 
   I want join all of that individual lists into a single one.*/
 storesList.stream()
                .map(Devices::getDevicesSubtype)
                .filter(Objects::nonNull)
                .map(subtype -> (MobileSubtype) subtype)
                .map(MobileSubtype::getPrices)
                .forEachOrdered(list -> pricesList.add(list));

storesList.stream()
                .map(Devices::getDevicesSubtype)
                .filter(Objects::nonNull)
                .map(subtype -> (MobileSubtype) subtype)
                .map(MobileSubtype::getInstructions)
                .forEachOrdered(list -> instructionsList.add(list));

storesList.stream()
                .map(Devices::getDevicesSubtype)
                .filter(Objects::nonNull)
                .map(subtype -> (MobileSubtype) subtype)
                .map(MobileSubtype::getSizes)
                .forEachOrdered(list -> sizesList.add(list));

/*How could i not repeat this part of the code and do the 3 for each ordered?*/
storesList.stream()
                .map(Devices::getDevicesSubtype)
                .filter(Objects::nonNull)
                .map(subtype -> (MobileSubtype) subtype)

>Solution :

Regarding your actual code, I’d suggest one forEach before mapping to a specific category, then add in each list

storesList.stream()
        .map(Devices::getDevicesSubtype)
        .filter(Objects::nonNull)
        .map(subtype -> (MobileSubtype) subtype)
        .forEachOrdered(subtype -> {
            pricesList.add(subtype.getPrices());
            instructionsList.add(subtype.getInstructions());
            sizesList.add(subtype.getSizes());
        });

Note : classes should be name at singular if there represent only one element, is Prices is one price, it should be name Price to avoid confusion, same for Instructions and Sizes