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javadictionarydata-structuresjava-streamdeque

Get a list of map keys from a deque in Java

I have a deque 

Deque<Map<int, String> cars = new LinkedList();

I want to use Java stream to collect all the keys from the deque map into a

List<int>.

Is there any way to do this?

I tried something like 

cars.stream().map(car -> car.keySet()).collect(Collectors.toList()

This question is different from the previous question. I want to collect all the keys, as opposed to removing a map from the deque.

Solution

  • Use flatMap():

    cars.stream()
    .map(Map::keySet)
    .flatMap(Set::stream)
    .collect(Collectors.toList())