How to convert Map<String, String> into String[], alternating between keys and values?

Question

I tried to find a way to convert Map<String,String> into String[] using Java 8 way.

A Map

{"A":"a", "B","b", "C", "c"}`

should be converted to

["A", "a", "B", "b", "C", "c"] or ["B", "b", "C", "c", "A", "a"] ...

The order of the pairs does not matter but key/value pairs must be together.

The old way to do this is obvious:

Map<String, String> headers = .......
String[] array = new String[headers.size() * 2];
int i = 0;
for(Map.Entry<String, String> entry : headers.entrySet()) {
    array[i++] = entry.getKey();
    array[i++] = entry.getValue();
}

what have you tried? look into the direction of creating a stream of entrySet — Naman
– Naman, Commented Jun 18, 2021 at 22:16
You can also do headers.forEach((k, v) -> { array[i++] = k; array[i++] = v; }); — shmosel
– shmosel, Commented Jun 18, 2021 at 23:39
Or with StreamEx: EntryStream.of(headers).flatMapKeyValue(Stream::of).toArray(String[]::new) — shmosel
– shmosel, Commented Jun 18, 2021 at 23:48

enzo · Accepted Answer · 2021-06-18 22:16:05Z

7

import java.util.Map;
import java.util.Arrays;
import java.util.HashMap;
import java.util.stream.Stream;

class Main {
    private static String[] transform(Map<String, String> map) {
        return map.entrySet().stream()
            .flatMap(entry -> Stream.of(entry.getKey(), entry.getValue()))
            .toArray(String[]::new);
    } 
    
    public static void main(String[] args) {
        Map<String, String> map = new HashMap<>();
        map.put("A", "a");
        map.put("B", "b");
        map.put("C", "c");
        
        String[] result = transform(map);

        System.out.println(Arrays.toString(result));
        // Output: [A, a, B, b, C, c]
    }
}

answered Jun 18, 2021 at 22:16

enzo

11.6k3 gold badges18 silver badges46 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to convert Map<String, String> into String[], alternating between keys and values?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related