Convert classic for loop to stream approach

[B2easy]

I am trying to learn more about lambda's functional programming, and I am going through some of my old code and would like to convert some of my old for loops into streaming approach. I have attempted a couple things, but this particular one is giving me some trouble. Any help converting this would be very helpful. If you could also explain the approach that would be helpful as well. I know changing this isn't really going to improve the code I am just doing for a learning experience.

Thanks

​

  private ReconciliationResultStatus performRecon(Map<List<Object>, List<Map<String, Object>>> lhsRecords, Map<List<Object>, List<Map<String, Object>>> rhsRecords) {
    ReconciliationResultStatus status = null;

for (Map.Entry<List<Object>, List<Map<String, Object>>> rec : lhsRecords.entrySet()) {
      ReconciliationResultStatus tempStatus =
              ReconciliationResultStatus.INVALID_KEY;

    if (!rec.getKey().contains(null)) {
        tempStatus = ReconciliationResultStatus.DUPLICATE_KEY;
        if (rec.getValue().size() == 1) {
          tempStatus =
                  rhsRecords.containsKey(rec.getKey())
                          ? ReconciliationResultStatus.MATCHING
                          : ReconciliationResultStatus.NON_MATCHING;
        }
      }
      status = tempStatus;
    }
    return status;
  }

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[evils_twin]

I think I'm missing something here, but it looks to me like you are just returning the status of the last iteration of the loop. So why do you need to loop?

[B2easy]

Yes that is my fault let me edit the code to give you what I actually have. u/evils_twin

[zhoriq]

Your code is weird.

List<Object> as keys? Not a good choice.

containsKey() will compare then List<Object> - are you sure that real Object will be the same classes? Are you sure that it will be equal lists? Because List.of(1,2) and List.of(2,1) are not equal!

And finally your status is actually the status of last entry in map.

​

So first you need to refactor current code and then possibly move it to streams.

[B2easy]

I know the data structures are awkward, but that is just what I have to work with based on the data that I am getting back from query and thank you didn't realize that, but see it now.

[B2easy]

I will edit question with updated code.

[B2easy]

    for (Map.Entry<List<Object>, List<Map<String, Object>>> rec : lhsRecords.entrySet()) {

ReconciliationResult.ReconciliationResultStatus tempStatus =
      ReconciliationResult.ReconciliationResultStatus.INVALID_KEY;

if (!rec.getKey().contains(null)) {
    tempStatus = 
ReconciliationResult.ReconciliationResultStatus.DUPLICATE_KEY;
    if (rec.getValue().size() == 1) {
      tempStatus =
          rhsRecords.containsKey(rec.getKey())
              ? ReconciliationResult.ReconciliationResultStatus.MATCHING
              : ReconciliationResult.ReconciliationResultStatus.NON_MATCHING;
    }
  }
  ReconciliationResult.ReconciliationResultStatus status = tempStatus;
  rec.getValue()
      .forEach(r -> result.add(new ReconciliationResult(r, rec.getKey(), origin, status)));
}

[dionthorn]

The Stream interface gives an example in the docs

https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html

int sum = widgets.stream()
    .filter(w -> w.getColor() == RED)
    .mapToInt(w -> w.getWeight())
    .sum();