How to convert string array to Big-integer array using Java 8 streams [duplicate]

Question

I have a String array and I want to convert it into BigInteger array using Java 8 streams.

String[] output = bigSorting(new String[]{"31415926535897932384626433832795", "1", "4900146572543628830293235422623540449026979", "10", "57500297590012603652986133599394871645776460", "5", 
                    "497010206818067722087306230802257700034825862515267073569769100385728461314", "57500297590012603652986133599394871645776460497010206818067722087306230802257700034825862515267073569769100385728461314497010206818067722087306230802257700034825862515267073569769100385728461314497010206818067722087306230802257700034825862515267073569769100385728461314497010206818067722087306230802257700034825862515267073569769100385728461314497010206818067722087306230802257700034825862515267073569769100385728461314"});
        Object[] unsortedBigIntegerArr = convertFromStringArrayToBigIntegerArray(output);

This is what I have tried but I am not able to get BigInteger array, I am able to get the Object array though.

private static Object[] convertFromStringArrayToBigIntegerArray(String[] unsorted) {
        return Arrays.stream(unsorted).map(BigSorting2::convertFromStringToBigInteger).toArray();
    }

    private static BigInteger convertFromStringToBigInteger(String unsorted) {
        return new BigInteger(unsorted);
    }

Is there any way I can do it completely using Java 8 streams.

Eugene · Accepted Answer · 2018-04-24 13:58:29Z

5

As simple as:

return Arrays.stream(unsorted)
             .map(BigSorting2::convertFromStringToBigInteger)
             .toArray(BigInteger[]::new);

answered Apr 24, 2018 at 13:58

Eugene

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10 Comments

pjj Over a year ago

Holy cow, this is wicked cool, thank you. Can you please suggest me best learning paths for Java8 streams.

Eugene Over a year ago

@pjj I'd start with Oracle tutorials really and the official documentation...

Jack Flamp Over a year ago

you could even do .map(BigInteger::new)

Anonymous Over a year ago

@pjj I learned quite a lot from Stack Overflow questions and answers. Search for the [java-stream] tag, for example.

Ousmane D. Over a year ago

@pjj to be honest most people unfamiliar with the Java type system would expect your attempt of Arrays.stream(unsorted).map(BigSorting2::convertFromStringToBigInteger).toArray(); to yield a Stream<BigInteger> but obviously this is not possible. due to a limitation of java one would have to explicitly specify an array constructor reference to retrieve an array of the expected type hence the .toArray(BigInteger[]::new); in the answer.

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OldCurmudgeon · Accepted Answer · 2018-04-24 14:18:48Z

0

Something really simple like:

public void test(String[] args) {
    String[] output = new String[]{"31415926535897932384626433832795", "1", "4900146572543628830293235422623540449026979", "10", "57500297590012603652986133599394871645776460", "5",
            "497010206818067722087306230802257700034825862515267073569769100385728461314", "57500297590012603652986133599394871645776460497010206818067722087306230802257700034825862515267073569769100385728461314497010206818067722087306230802257700034825862515267073569769100385728461314497010206818067722087306230802257700034825862515267073569769100385728461314497010206818067722087306230802257700034825862515267073569769100385728461314497010206818067722087306230802257700034825862515267073569769100385728461314"};
    Object[] bigIntegers = Arrays.stream(output)
            .map(BigInteger::new)
            .toArray();
    System.out.println(Arrays.toString(bigIntegers));
}

edited Apr 24, 2018 at 14:18

answered Apr 24, 2018 at 13:59

OldCurmudgeon

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2 Comments

pjj Over a year ago

I think you mis-understood my question, please see my question or @Eugene answer, thanks for your answer though.

Anonymous Over a year ago

As I understood the question it was whether it was possible to get a BigInteger[] rather than an Object[] from the String[].

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