how to extract all integers from an array of random characters and transfer them to the array

Question

, i do not know how to correctly write this code.

My code:

    String str = "23g32./'ef3";
    int[] arr = new int[str.length()];
    for (int digitsCount = 0; digitsCount < str.length(); digitsCount++)
        for (int digitsArrayIndex = 0; digitsArrayIndex < str.length(); digitsArrayIndex++) {
            if (Character.isDigit(str.charAt(digitsArrayIndex))) {
                arr[digitsArrayIndex] = Integer.parseInt(String.valueOf(str.charAt(digitsArrayIndex)));
            }

        }
    System.out.println("Array: " + Arrays.toString(arr));
}

My output:

Array: [2, 3, 0, 3, 2, 0, 0, 0, 0, 0, 3]

I want:

Array: [2, 3, 3, 2, 3]

Answer 1

A simpler way would be just to use one loop, and another index. When you have filled in the array, copy it using the value of the index

String str = "230g32./'ef3";
int index = 0;
int[] arr = new int[str.length()];
for (int digitsArrayIndex = 0; digitsArrayIndex < str.length(); digitsArrayIndex++) {
    if (Character.isDigit(str.charAt(digitsArrayIndex))) {
        arr[index++] = Integer.parseInt(String.valueOf(str.charAt(digitsArrayIndex)));
    }
}

System.out.println("Array: " + Arrays.toString(Arrays.copyOf(arr, index)));

Answer 2

You can go more declarative and use Stream API for it:

  final List<Character> filteredCharacters = str.chars()
      .mapToObj(i -> (char) i)
      .filter(Character::isDigit)
      .collect(Collectors.toList());

Answer 3

One easy approach here would be to just do a regex replacement on the input string to strip away any non digits. Then, just use the character array from the resulting string.

String str = "23g32./'ef3";
char[] output = str.replaceAll("\\D+", "").toCharArray();
System.out.println(Arrays.toString(output));  // [2, 3, 3, 2, 3]

Answer 4

You can use Character.isDigit() :

String str = "23g32./'ef3";
List<Integer> digits = new ArrayList<>();

for (char c : str.toCharArray()) {
    if(Character.isDigit(c)){
        digits.add(c - '0');
    }
}

System.out.println(digits);

Output:

[2, 3, 3, 2, 3]

Answer 5

tl;dr

Never use obsolete char , use only code point integers.

 "23g32./'ef3".codePoints().filter( Character::isDigit ).map( Character::getNumericValue ).toArray()

See that code run live at IdeOne.com .

[2, 3, 3, 2, 3]

Code points

The char type in Java is obsolete, unable to represent even half of the characters defined in Unicode. Instead, learn to use code point integer numbers.

The String#codePoints method returns an IntStream , that is, a stream of the code point integers, one for each character in your input string.

For each code point, ask if that character represents a digit as designated by the Unicode standard. If so, collect it. If not, ignore it.

Convert each of those digit characters into a number. Collect the numbers into your final array.

int[] digits =
        "23g32./'ef3"
                .codePoints()
                .filter(
                        Character::isDigit
                )
                .map(
                        Character::getNumericValue
                )
                .toArray();

digits = [2, 3, 3, 2, 3]

Often a List is more convenient than a mere array.

List < Integer > digits =
        "23g32./'ef3"
                .codePoints()
                .filter(
                        codePoint -> Character.isDigit( codePoint )   // Or: Character::isDigit
                )
                .map(
                        codePoint -> Character.getNumericValue( codePoint )   // Or: Character::getNumericValue
                )
                .boxed()
                .collect( Collectors.toList() )   // Or, in Java 16+, simply `.toList()`
;

See this code run live at IdeOne.com .

digits = [2, 3, 3, 2, 3]