How can I use two arrays to create a HashMap in Java 8? [duplicate]

Question

I have two arrays of Strings. How can I loop through both arrays at once to create a HashMap<String, String> where the key is coming from first array and the value is coming from the second array?

eg.

Array1 = {"A", "B", "C", "D"}
Array2 = {"apple", "boy", "cat", "dog"}

Resulting HashMap:

[{A:apple}, {B:boy}, {C:cat}, {D:dog}]

Here is my code, but it's not working.

AtomicInteger index = new AtomicInteger();
Stream<String> stream = Stream.of(array2);
stream.forEach(x -> mappedData.put(array1[index.getAndIncrement()],x));

btw you could accept an answer here... meta.stackexchange.com/questions/5234/… — Eugene
– Eugene, Commented May 17, 2018 at 8:58

Eugene · Accepted Answer · 2018-05-02 08:31:51Z

3

Assuming they have the same size, there are no duplicates or nulls:

IntStream.range(0, first.length)
         .mapToObj(x -> new SimpleEntry<>(first[x], second[x]))
         .collect(Collectors.toMap(Entry::getKey, Entry::getValue))

you can replace SimpleEntry with Arrays.asList or in java-9 List.of also

Or:

IntStream.range(0, first.length)
         .boxed()
         .collect(Collectors.toMap(x -> first[x], y -> second[y]))

edited May 2, 2018 at 8:31

answered May 2, 2018 at 8:18

Eugene

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3 Comments

Holger Over a year ago

Or Java 9’s Map.entry(…, …).

Lino Over a year ago

instead of assuming they are equal length you could also use IntStream.range(0, Math.min(first.length, second.length))

Eugene Over a year ago

@Lino I thought about that... but was not sure what the OP would think about it as his example has them to be same length. Still, thx for he addition

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