Using Java 8 Streams how to convert an Array of Enum Objects to an other Enum Array

Question

Using Java 8 Streams how to convert an Array of Enum Objects to an other Enum Object Array

Class Structure

 enum QUESTIONS {
        CONTACT_QUESTION,
        ADDRESS_QUESTION,
        WORK_QUESTION
    };

 enum CODES {
       CQ,
       AQ,
       WQ
    };

INPUT

CODES[] firstSet_Short = {CODES.CQ, CODES.AQ}

OUTPUT

QUESTIONS[] firstSet_Long = {QUESTIONS.CONTACT_QUESTION, QUESTIONS.ADDRESS_QUESTION}

What's the background/context for that mapping ? Seems there's a better solution in surrounding design than solving by streaming. — hc_dev
– hc_dev, Commented Feb 14, 2019 at 21:59
context is api-of-backend returns a enum of codes(shorter ones) while the frontend need an enum of questions(longer version) — surreal_sai
– surreal_sai, Commented Feb 14, 2019 at 22:09
Possibly related/dupe stackoverflow.com/questions/32709686/two-related-enums-mapping — Naman
– Naman, Commented Feb 15, 2019 at 2:48

Kartik · Accepted Answer · 2019-02-14 23:39:48Z

1

Here I am matching the initials of the codes like C***_Q***:

CODES[] firstSet_Short = {CODES.CQ, CODES.AQ};

List<QUESTIONS> result = Arrays.stream(firstSet_Short)
        .map(c -> Arrays.stream(QUESTIONS.values())
                .filter(q -> q.toString().matches(c.toString().charAt(0) + ".+_" + c.toString().charAt(1) + ".+"))
                .findFirst().orElse(null))
        .collect(Collectors.toList()); //or .toArray(QUESTIONS[]::new); if you want array

System.out.println(result);

Output

[CONTACT_QUESTION, ADDRESS_QUESTION]

A better way would be to store a mapping in CODES like this:

enum CODES {
    CQ(QUESTIONS.CONTACT_QUESTION),
    AQ(QUESTIONS.ADDRESS_QUESTION),
    WQ(QUESTIONS.WORK_QUESTION);

    private QUESTIONS question;

    CODES(QUESTIONS question) {
        this.question = question;
    }

    public QUESTIONS getQuestion() {
        return question;
    }
}

And then your code will become:

QUESTIONS[] result = Arrays.stream(firstSet_Short)
        .map(CODES::getQuestion)
        .toArray(QUESTIONS[]::new);

edited Feb 14, 2019 at 23:39

answered Feb 14, 2019 at 23:29

Kartik

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1 Comment

Naman Over a year ago

The solution suggested latter, should be the way one could say, since the server as mentioned by OP could then be sending AMAZNING_QUESTION and clients can still represent it as AQ. But maybe they might be looking for a reversed mapping in my opinion.

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