Syntax error when using conditional operator inside Stream.map

Question

I am working on a Java project where I have to use a Java stream to collect IDs of all the objects inside a list of objects.

Now I only want to collect IDs of those objects whose type matches a certain value.

What I am using:

List<String> skuGroupIds = skuGroupPagedResponseMap.getData().stream().map(this::getGroupId).collect(Collectors.toList());

Now I want to use the condition and I did this but this is giving syntax error:

List<String> skuGroupIds = skuGroupPagedResponseMap.getData().stream().map(group->group.getCreatedType().equals(SkuGroupCreationType.SKU_GROUP_LOT)?this::getGroupId:return null;).collect(Collectors.toList());

getGroupID function used inside map

private String getGroupId(SkuGroupResponseDTO skuGroupResponseDTO){
    return skuGroupResponseDTO.getSkuId() + Constants.HYPHEN + skuGroupResponseDTO.getId();
}

How can I fix this so it doesn't cause a syntax error?

Answer 1

Your lambda inside map(), should look like this:

.map(group -> group.getCreatedType().equals(SkuGroupCreationType.SKU_GROUP_LOT) ? this::getGroupId : null)

Or like this:

.map(group -> {
    return group.getCreatedType().equals(SkuGroupCreationType.SKU_GROUP_LOT) ? this::getGroupId : null;
})

But it would be much better to use a filter(), as mentioned in comments:

List<String> skuGroupIds = skuGroupPagedResponseMap.getData()
     .stream()
     .filter(group -> group.getCreatedType().equals(SkuGroupCreationType.SKU_GROUP_LOT))
     .map(this::getGroupId)
     .collect(Collectors.toList());