Convert double to int array

Question

I have a double

double pi = 3.1415;

I want to convert this to a int array

int[] piArray = {3,1,4,1,5};

I came up with this

double pi = 3.1415;
String piString = Double.toString(pi).replace(".", "");
int[] piArray = new int[piString.length()];
for (int i = 0; i <= piString.length()-1; i++)
   piArray[i] = piString.charAt(i) - '0'; 

It's working but I don't like this solution because I think a lot of conversions between datatypes can lead to errors. Is my code even complete or do I need to check for something else?

And how would you approach this problem?

Answer 1

I don't know straight way but I think it is simpler:

int[] piArray = String.valueOf(pi)
                      .replaceAll("\\D", "")
                      .chars()
                      .map(Character::getNumericValue)
                      .toArray();

Answer 2

Since you want to avoid casts, here's the arithmetic way, supposing you only have to deal with positive numbers :

List<Integer> piList = new ArrayList<>();
double current = pi;
while (current > 0) {
    int mostSignificantDigit = (int) current;
    piList.add(mostSignificantDigit);
    current = (current - mostSignificantDigit) * 10;
}

Handling negative numbers could be easily done by checking the sign at first then using the same code with current = Math.abs(pi).

Note that due to floating point arithmetics it will give you results you might not expect for values that can't be perfectly represented in binary.

Here's an ideone which illustrates the problem and where you can try my code.

Answer 3

int[] result = Stream.of(pi)
            .map(String::valueOf)
            .flatMap(x -> Arrays.stream(x.split("\\.|")))
            .filter(x -> !x.isEmpty())
            .mapToInt(Integer::valueOf)
            .toArray();

Or a safer approach with java-9:

 int[] result = new Scanner(String.valueOf(pi))
            .findAll(Pattern.compile("\\d"))
            .map(MatchResult::group)
            .mapToInt(Integer::valueOf)
            .toArray();