Use Streams to return Boolean if all the List values in a Map are empty/not-empty

Question

Given a Map mapping a String to a List, is there a way to use Java Streams to return a Boolean where TRUE means one or more list had elements? If all lists in the map were e

Answer 1

int size = Map.entrySet().stream()
                           .map(entry -> entry.getValue())
                           .flatMap(list -> list.stream())
                           .size();
if(size==0)
  return Boolean.False;
else
  return Boolean.True;

This code is a simple one this may help for your work .

Answer 2

Stream::allMatch

In Java 8 you can check that not all lists are empty.

 boolean anyNonEmpty = !map.values().stream().allMatch(List::isEmpty);

Notice that Stream::allMatch is a short-circuiting terminal operation. So the stream is efficient, not running any longer than need be.

Answer 3

Use the anyMatch method that finds if any element of the stream matches a Predicate. Here, your predicate is that the entry's value (the list) is not empty.

boolean anyNonEmpty = map.entrySet()
    .stream()
    .anyMatch(entry -> !entry.getValue().isEmpty());