Separate String Number Letters

Question

I need to separate the characters of a string into numbers and letters.

Ex.:

Entree:

"A1B2C3D2Z9"

Exit:

List<Character> numeros = { '1','2', '3' }
List<Character> letras = { 'A', 'B', 'C' }

Use a for to traverse the string, only that I don’t know how to identify in the condition that checks whether the position of the string is a number or a letter.

Does anyone know how I can take this conditional test?

Answer 1

Check if the character is a number, using Character.isDigit().

It is good to note that other symbols can be used. So it would be good to use also the method Character.isLetter() to validate if the character is really a letter. (Thanks to @diegofm for noticing this).

Below the validating code, letters, numbers and other character types.

String input = "A1B2C3D2Z9®*#"; //adicionei uns símbolos pro exemplo fazer sentido

List<Character> letras = new ArrayList<>();
List<Character> numeros = new ArrayList<>();
List<Character> outros = new ArrayList<>();

for (char c : input.toCharArray()) {
    if (Character.isDigit(c)) {
        numeros.add(c);
    } else if (Character.isLetter(c)) {
        letras.add(c);
    } else {
        outros.add(c);
    } 
}

^{I put the code on Github for future reference.}

Answer 2

In the library of Character has a method isDigit that checks if the character is a number of 0-9

char c = string.charAt(0);
if (Character.isDigit(c)) {
    //É numero
} else {
    //É letra
}

In this question of the O Gringo has several ideas: https://stackoverflow.com/questions/1223052/how-do-i-find-out-if-first-character-of-a-string-is-a-number

Answer 3

Simple alternative using replaceAll and regex

String input = "A1B2C3D2Z9";
String letters = input.replaceAll("[^a-zA-Z]+", "");
String numbers = input.replaceAll("[^0-9]+", "");

//Para transformar em array
letters.toCharArray();
numbers.toCharArray();

Answer 4

It’s just the solution of the same problem with another flavor.

String chars = "A1B2C3D44F555";
List <Character> letters = chars.chars().
                              boxed().
                              map(ch -> (char) ch.intValue()).
                              filter(Character::isLetter).
                              collect(Collectors.toList());
List <Character> digits = chars.chars().
                             boxed().
                             map(ch -> (char) ch.intValue()).
                             filter(Character::isDigit).
                             collect(Collectors.toList());

This solution is slower by doing Autoboxing twice on the list.