CODEWITHSUNDEEP
javacollectionslambdajava-8
OTUser
OTUser

Reputation: 3848

Java 8 : Map Lambda expression

I have a Map<String, List<Object>> multiFieldMap and I need to itereate over its value set and add the value to multiFieldsList as below

public List<Object> fetchMultiFieldsList() {
    List<Object> multiFieldsList = new ArrayList<Object>();
    for (Entry<String, List<Object>> entry : multiFieldMap.entrySet()) {
        String entityName = entry.getKey();
        List<Object> ids = entry.getValue();
        for (Object id : ids) {
            Object entity = queryService.query(entityName, queryService.property("id").eq(id));
            multiFieldsList.add(entity);
        }
    }
    return multiFieldsList;
}

Am wondering can this method be simplified further?

Upvotes: 8

Views: 27159

Answers (3)

Holger
Holger

Reputation: 298143

You can simplify it like this:

public List<Object> fetchMultiFieldsList() {
    List<Object> multiFieldsList = new ArrayList<>();
    multiFieldMap.forEach( (entityName, ids ) ->
        ids.forEach( id -> multiFieldsList.add(
            queryService.query(entityName, queryService.property("id").eq(id)))
        )
    );
    return multiFieldsList;
}

Unless you want to use the Stream API, the method Map.forEach might be the biggest win regarding code simplification as you don’t need to deal with Map.Entry and its generic signature anymore…

Upvotes: 2

Eran
Eran

Reputation: 393801

You can use the Streams API :

List<Object> multiFieldsList = 
    multiFieldMap.entrySet()
                 .stream()
                 .flatMap(e -> e.getValue()
                                .stream()
                                .map(o -> queryService.query(e.getKey(), queryService.property("id").eq(o))))
                 .collect(Collectors.toList());

Upvotes: 6

fge
fge

Reputation: 121710

You can indeed use a stream to simplify you inner loop.

You can replace:

List<Object> ids = entry.getValue();
for (Object id : ids) {
    Object entity = queryService.query(entityName, queryService.property("id").eq(id));
    multiFieldsList.add(entity);
}

with:

entry.getValue().map(
    id -> queryService.query(entityName, queryService.property("id").eq(id))
).forEach(multiFieldsList::add);

But you don't really gain much from that. Your choice...

See @Eran's answer for a "full stream" solution.

Upvotes: 2

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