Error in lambda function in Java while handling list

Question

I have recently switched from C++ to Java and facing tough times to deal with the syntax and lambda functions. So there is one method which got updated. I am confused editing the code correspondingly.

So initially getCostChangeDtl() used to return data of type CostChangeDtl but now the same method returns a list of CostChangeDtl. So I made some changes accordingly still facing some issues.

Before

costChangeDetails.forEach(
            costChangeDetail -> changeDtls.addAll(costChangeDetail.getItems().stream().map(item -> {
                CostChangeDtl despCostChangeDtl = getCostChangeDtl(ccd, costChangeDetail, item,
                    metrics);
                        
                            if (despCostChangeDtl.getItemID() == null)
                            {
                                String consumerGtin = item.item.getConsumerDetails().getConsumerGtin();
                                missingSkuGtins.add(
                                        format("%s | %s ", consumerGtin, costChangeDetail.getLocation().getId()));
                            }
                        
                        return despCostChangeDtl;
                    }).filter(despCostChangeDtl -> despCostChangeDtl.getItemID() != null)
                .collect(Collectors.toList())));

After

costChangeDetails.forEach(
            costChangeDetail -> changeDtls.addAll(costChangeDetail.getItems().stream().map(item -> {
                List<CostChangeDtl> despCostChangeDtl = getCostChangeDtl(ccd, costChangeDetail, item,
                    metrics);
                        for (CostChangeDtl costChangeDtl : despCostChangeDtl) {
                            if (costChangeDtl.getItemID() == null)
                            {
                                String consumerGtin = item.item.getConsumerDetails().getConsumerGtin();
                                missingSkuGtins.add(
                                        format("%s | %s ", consumerGtin, costChangeDetail.getLocation().getId()));
                            }
                        }
                        return despCostChangeDtl;
                    }).filter(despCostChangeDtl -> despCostChangeDtl.getItemID() != null)
                .collect(Collectors.toList())));

Now I am getting an error in despCostChangeDtl.getItemID() as expected since it is despCostChangeDtl is now a list. How to fix this particular issue?

Hi, I did not run the code so did not any error msg as such. I was getting error from the IDE itself. in the .filter() despCostChangeDtl is a list. so despCostChangeDtl.getItems() is invalid we need to loop through. I am facing issue while fixing this part. — Deepjyoti De
– Deepjyoti De, Commented Nov 26, 2021 at 8:20
Have you tried changing despCostChangeDtl to literally anything else inside your call to filter(), and prepending a call to stream() before you call filter()? — JustAnotherDeveloper
– JustAnotherDeveloper, Commented Nov 26, 2021 at 8:28
I think you will have to split this into 2 steps. Collect all your List<CostChangeDtl> in step 1. Then apply filter over all the items in step 2. I will post an answer separately because it difficult to write it here. — Sree Kumar
– Sree Kumar, Commented Nov 26, 2021 at 8:33

rongfeiyue · Accepted Answer · 2021-11-26 08:44:43Z

1

despCostChangeDtl from an object to a list, so you should flatmap after map.

edited Nov 26, 2021 at 8:44

answered Nov 26, 2021 at 8:32

rongfeiyue

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2 Comments

rongfeiyue Over a year ago

After map opt, stream was Stream<List<CostChangeDtl>>. Use flatMap(List::Stream) change the stream to Stream<CostChangeDtl>.

Deepjyoti De Over a year ago

That seems to have resolved the error at least it is not giving red marks in the IDE

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