List<String> userNames = StreamEx.of(users).map(User::getName).toList();
Map<Role, List<User>> role2users = StreamEx.of(users).groupingBy(User::getRole);
StreamEx.of(1,2,3).joining("; "); // "1; 2; 3"

public List<Element> elementsOf(NodeList nodeList) {
    return IntStreamEx.range(nodeList.getLength())
      .mapToObj(nodeList::item).select(Element.class).toList();
}

public List<String> getDropDownOptions() {
    return StreamEx.of(users).map(User::getName).prepend("(none)").toList();
}

public int[] addValue(int[] arr, int value) {
    return IntStreamEx.of(arr).append(value).toArray();
}

public void copyNonEmptyLines(Reader reader, Writer writer) throws IOException {
    for(String line : StreamEx.ofLines(reader).remove(String::isEmpty)) {
        writer.write(line);
        writer.write(System.lineSeparator());
    }
}

Map<String, Role> nameToRole;

public Set<String> getEnabledRoleNames() {
    return StreamEx.ofKeys(nameToRole, Role::isEnabled).toSet();
}

public Map<String, List<String>> invert(Map<String, List<String>> map) {
    return EntryStream.of(map).flatMapValues(List::stream).invert().grouping();
}

public Map<String, String> stringMap(Map<Object, Object> map) {
    return EntryStream.of(map).mapKeys(String::valueOf)
        .mapValues(String::valueOf).toMap();
}

Map<String, Group> nameToGroup;

public Map<String, List<User>> getGroupMembers(Collection<String> groupNames) {
    return StreamEx.of(groupNames).mapToEntry(nameToGroup::get)
        .nonNullValues().mapValues(Group::getMembers).toMap();
}

DoubleStreamEx.of(input).pairMap((a, b) -> b-a).toArray();

short[] multiply(short[] src, short multiplier) {
    return IntStreamEx.of(src).map(x -> x*multiplier).toShortArray(); 
}

static <T> StreamEx<T> scanLeft(StreamEx<T> input, BinaryOperator<T> operator) {
        return input.headTail((head, tail) -> scanLeft(tail.mapFirst(cur -> operator.apply(head, cur)), operator)
                .prepend(head));
}