Java 8: how to create a map out from two String lists

Question

I have two lists:

List<String> ids
List<String> names

The task is to create one Map<String,String> out of these two lists, preferably using Java 8. Unfortunatly, I did not find how to make it when we have lists with String type.

The question is not clear. Which should be the key - I guess ids? Are the ids unique. Are the lists the same size? How should they be grouped? — HectorLector
– HectorLector, Commented Nov 6, 2018 at 17:38

Pankaj Singhal · Accepted Answer · 2018-11-06 17:44:04Z

1

Assuming both the lists have the same size & ids are unique & ids are the keys of the map and names are corresponding values, you can use the following code to create a map:

Map<String,String> idsNames = IntStream.range(0,ids.size())
        .mapToObj(i -> new AbstractMap.SimpleEntry<>(ids.get(i),names.get(i)))
        .collect(Collectors.toMap(AbstractMap.SimpleEntry::getKey,
                AbstractMap.SimpleEntry::getValue));

answered Nov 6, 2018 at 17:44

Pankaj Singhal

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2 Comments

Igor Vlasuyk Over a year ago

Yes, it works. Sorry if my question was not very clear.

fps Over a year ago

There's no need to create an intermediate Map.Entry for each i. Just using IntStream.range(0,ids.size()).boxed().collect(Collectors.toMap(ids::get, names::get)) should suffice. It's also worth mentioning that this approach works well if both lists are random access, i.e. ArrayList.

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