Convert Java Map Enum keys to Map String keys

Question

I have the following map:

Map<DataFields, String> myMap;

But I need to convert it to the following:

Map<String, String> myMap;

My best feeble attempt which doesn't even compile is:

myMap.keySet().stream().map(k -> k.name()).collect(Collectors.toMap(k, v)

I think you might need to use entrySet() instead of keySet(). — clinomaniac
– clinomaniac, Commented Feb 27, 2018 at 18:43
not sure if FP reduces any efficiency. Another answer stackoverflow.com/questions/17208346/… — Adesh Kumar
– Adesh Kumar, Commented Feb 27, 2018 at 19:10
Also, not sure why you needed such a map. Wherever you have to use this map you could have effectively converted the key to string and then used. — Adesh Kumar
– Adesh Kumar, Commented Feb 27, 2018 at 19:11

Mureinik · Accepted Answer · 2018-02-27 18:44:45Z

9

You need to stream the entrySet() (so you have both the keys and the values), and collect them to a map:

Map<String, String> result =
    myMap.entrySet()
         .stream()
         .collect(Collectors.toMap(e -> e.getKey().name(), e -> e.getValue()));

answered Feb 27, 2018 at 18:44

Mureinik

316k54 gold badges399 silver badges405 bronze badges

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

5 Comments

Eugene Over a year ago

e -> e.getValue() replace with Entry::getValue

Adesh Kumar Over a year ago

Eugene it's just a syntactic sugar. Any performance advantage of using Entry::getValue

Eugene Over a year ago

@AdeshKumar first, unless you tag me with @, I can't tell you commented, second is that a question or an affirmation?

Louis Wasserman Over a year ago

Yes, it's advantageous for both performance and readability to use method references where possible.

Eugene Over a year ago

@AdeshKumar a lambda expression will create one more synthetic method, while method references will not, that's about the only difference (besides readability)

kasopey · Accepted Answer · 2018-02-27 18:56:02Z

2

Map<String, String> result = myMap
    .entrySet() // iterate over all entries (object with tow fields: key and value)
    .stream() // create a stream
    .collect(Collectors.toMap(e -> e.getKey().toString(), e -> e.getValue()));
        // collect to map: convert enum Key value toString() and copy entry value

edited Feb 27, 2018 at 18:56

answered Feb 27, 2018 at 18:50

kasopey

3754 silver badges18 bronze badges

1 Comment

NastyDiaper Over a year ago

I'd prefer to use name() over toString() which is the reason I'll accept the other answer.

Vinay Prajapati · Accepted Answer · 2018-02-27 19:04:37Z

2

Another way of doing same without Collectors helper. Using entryset will make it very easy to map.

  map.entrySet()
                .stream()
                .collect(
                        () -> new HashMap<String, String>(),
                        (Map newMap, Map.Entry<DataFields, String> entry) -> {
                            newMap.put(entry.getKey().name(), entry.getValue());
                        }
                        ,
                        (Map map1, Map map2) -> {
                            map.putAll(map2);
                        }
                );

answered Feb 27, 2018 at 19:04

Vinay Prajapati

7,59012 gold badges51 silver badges88 bronze badges

Comments

fps · Accepted Answer · 2018-02-27 20:36:55Z

2

A Java 8, succint way to do it (without streams):

Map<String, String> result = new HashMap<>();
myMap.forEach((k, v) -> result.put(k.name(), v));

answered Feb 27, 2018 at 20:36

fps

34.5k8 gold badges62 silver badges116 bronze badges

Collectives™ on Stack Overflow

Convert Java Map Enum keys to Map String keys

4 Answers 4

5 Comments

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

5 Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related