How to get a keySet of HashMap filter by boolean value in Java?

Question

Map map = new HashMap<Long, Boolean>();
map.keySet(); // filtering the true value

Answer 1

You can filter over the entrySet and then use map to only obtain the keys with streams.

Set<Long> resultKeys = map.entrySet().stream().filter(Map.Entry::getValue)
    .map(Map.Entry::getKey).collect(Collectors.toSet());

Demo

Answer 2

Try it like this. You're filtering the Map.Entry on the value and then mapping the entry to the key .

Map<Long, Boolean> map =
        Map.of(1L, true, 2L, false, 3L, true, 4L, false);
Set<Long> set = map.entrySet().stream()
        .filter(Entry::getValue).map(Entry::getKey)
        .collect(Collectors.toSet());
System.out.println(set);

Prints

[1, 3]

Answer 3

You can iterate over the map's entry set, and add the key to a set if the value is true :

public static void main(String[] args) {
    Map<Long, Boolean> map = new HashMap<Long, Boolean>(); 
    map.put(1l,true); map.put(2l,false); map.put(3l,true);
    Set<Long> validKeys = getValidKeys(map);
    System.out.println(validKeys);
}
private static Set<Long> getValidKeys(Map<Long, Boolean> map) {
    Set<Long> set = new HashSet<>();
    for(Map.Entry<Long, Boolean> entry : map.entrySet()) {
        if(entry.getValue()) set.add(entry.getKey());
    }
    return set;
}

Output:

[1, 3]