Basil Bourque February 2016

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

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 empty, return FALSE.

Map< String , List<String> > map = …

Can use of Streams replace this conventional code?

// See if any diffs were found. Loop through the Map, look at each List of diffs to see if non-empty.
boolean anyElementsInAnyList = false;
for (List<String> list : map.values () ) {
    if (!list.isEmpty()) {
        anyElementsInAnyList = true;
        break;
    }
}

Note that we can break out of the examination after the first finding. No need to examine all the Map values (all the Lists). Would be nice if, for efficiency, the Stream could do the same stop-work-on-first-finding (a “short-circuiting” operation).

Answers


rgettman February 2016

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());


Peter Lawrey February 2016

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

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


Akhil February 2016

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 .

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Asked in February 2016
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