How to filter “Null” values from HashMap? [duplicate]

Answer 1

that will work

Map<String, String> result = map.entrySet()
    .stream()
    .filter(e -> e.getValue() != null)
    .collect(Collectors.toMap(p -> p.getKey(), p -> p.getValue()));

Answer 2

You can use the Java 8 method Collection.removeIf for this purpose:

map.values().removeIf(Objects::isNull);

This removed all values that are null.

Online demo

This works by the fact that calling .values() for a HashMap returns a collection that delegated modifications back to the HashMap itself, meaning that our call for removeIf() actually changes the HashMap (this doesn't work on all java Map's)

Answer 3

If you are using pre-Java 8, you can use:

Collection<String> values = map.values();
while (values.remove(null)) {}

This works because HashMap.values() returns a view of the values, and:

The collection [returned by HashMap.values()] supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations

An alternative way that might be faster, because you don't have to keep re-iterating the collection to find the first null element:

for (Iterator<?> it = map.values().iterator();
    it.hasNext();) {
  if (it.next() == null) {
    it.remove();
  }
}

Or you can do it without the explicit iteration:

values.removeAll(Collections.singleton(null));