How to calculate mask using java stream

Question

I have this code. Here the map is Map<Data, Boolean>

int mask = 0;
for (Map.Entry<Data, Boolean> entry : map.entrySet()) {
  if (entry.getKey().getValue() > 0 && entry.getValue()) {
    mask = mask | (1 << (entry.getKey().getValue() - 1));
  }
}

I want to calculate mask using Java stream. Here I tried to but only get then filter list. Don't know how calculate the mask here.

Integer mask = map.entrySet().filter( entry -> entry.getKey().getValue() > 0 && entry.getValue()).?

Answer 1

You can map your entry to the calculated value and then apply the or within a reduce operator:

map.entrySet().stream()
       .filter(entry -> entry.getValue() && entry.getKey().getValue() > 0)
       .mapToInt(entry -> (1 << (entry.getKey().getValue() - 1)))
       .reduce(0, (r, i) -> r | i)

Edit: Added 0 as identity element to the reduce operation to have a default value of 0 if the map is empty.

Edit2: As suggested in the comments I reversed the filter order to avoid unnecessary method calls

Edit3: As suggested in the comments mapToInt is now used

Answer 2

You can try this , but as Aniket said above here mask is mutating not a good idea to use Strem.

map.entrySet().filter( entry -> entry.getKey().getValue() > 0 && entry.getValue()).forEach(k->{mask=mask | (1 << (k.getKey().getValue() - 1))});