convert java for loop into stream with filter

Question

I have transformed a regular for loop code into java 8 streams. I tried a few, but i am still learning this and running out of ideas, please suggest ideas. can this be further simplified ? Other than using forEach, I am not able to change much. Also, why do I have to typecast the eid to String in getERecordFromId((String)eid)

Stream <String>eIdsStream = getEidStream();

final HashSet<String> declinedRecords = new HashSet<>();

eIdsStream.forEach (eid ->  {
        ERecord eRecord = getERecordFromId((String)eid);
        if(eRecord.getEHash() != null &&  Status.DECLINED == eRecord.getStatus()) {
            declineRecords.add(eRecord.getEHash());
        }
    }

Replacing your for-each loops with Stream.forEach might not be a great idea. — Jiri Tousek
– Jiri Tousek, Commented May 24, 2019 at 6:32
Now that you changed your variable to a Stream<String>, you don't need the casting to String, so at least that part of your question is no longer relevant (perhaps you should edit it out). — Eran
– Eran, Commented May 24, 2019 at 7:03

Eran · Accepted Answer · 2019-05-24 06:29:28Z

6

The casting is required since you use a raw Stream variable. Assuming getEidStream() returns a Stream<String>, you should have assigned it to a Stream<String> variable, or not assigned it to a variable at all.

Using forEach defeats the purpose of using Streams in the first place.

You should use filter and map to transform the Stream to hold the required elements, and then collect to a Set.

Set<String> declinedRecords =
    getEidStream().map(eid -> getERecordFromId(eid))
                  .filter(eRecord -> eRecord.getEHash() != null &&  Status.DECLINED == eRecord.getStatus())
                  .map(ERecord::getEHash)
                  .collect(Collectors.toSet());

edited May 24, 2019 at 6:29

answered May 24, 2019 at 6:25

Eran

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9 Comments

priyanksriv Over a year ago

And to answer your question about casting eid, it's because you have defined a Stream without specifying the generic parameter Stream<String>.

Roma Over a year ago

ok.. this makes sense. but I get compile error for eRecord.getEHash() and eRecord.getStatus() --- cannot resolve method and also ERecord::getEHash -- cannot access non static method as static

Eran Over a year ago

@Roma what kind of method is getEHash? Is it an instance method of ERecord or a static method of that class? The eRecord.getEHash() call in your question suggests it's an instance method. You can always replace it with a lambda expression if the method reference doesn't work (eRecord -> eRecord.getEHash())

Roma Over a year ago

it is an instance method of ERecord.

Eran Over a year ago

@Roma Does the code in your question pass compilation?

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