How do I break a string into groups of letters with a loop in Java?

Question

I have to write a method which breaks a string into groups. The user should give the amount of letters per group and the function should return a string that consists of the input string broken into groups. For instance, function(“HELLOYOU”, 2) would return “HE LL OY OU”.

Answer 1

You can use String.split() to break the string into an array of individual letters, and then combine pairs of letters, or larger groups, etc.

Here is some example code:

String[] splitInParts(String input, int size) {
    String[] letters = input.split("");
    String[] output = new String[letters / size];

    for (int i = 0; i < output.length; i++) {
        output[i] = "";
        for (int j = 0; j < size; j++) {
            output[i] = output[i] + letters[size * i + j];
        }
    }

    return output;
}

There is a lot of boilerplate code missing, for example, checking that loop parameters are in range, checking strings are not null, etc. However this is a rough idea of how you could go about doing it.

Answer 2

You can move the characters of input String to a new String and put whitespaces on every step that equals to "size":

String function(String input, int parts) {
    StringBuilder result = new StringBuilder();
    int partCounter = 0;
    for (int i = 0; i < input.length(); i++) {
        partCounter++;
        result.append(input.charAt(i));
        if (partCounter == parts){
            result.append(" ");
            partCounter = 0;
        }
    }

    return result.toString();
}

Answer 3

You could use the below code that takes in a String instance and aN int defining the number of characters to split based on. And then use the String instances split method .

public static String[] split(String input, int len){
    // To prevent any NullPointerException being thrown
    if (StringUtils.isEmpty()) {
        return null;
    }
    // Split the input string based on a regex pattern
    return input.split(String.format("(?<=\\G.{%1$d})", len));
}

The Regular Expression that is being used here is (?<=\\\\G.{%1$d}) which based on len being 2 would become (?<=\\\\G.{2}) . So this means it would split every 2 characters. So the output for a string of HELLOWORLD would be HE , LL , OW , OR , LD .

If you wanted to join those into one String separated by a space you could using the StringUtils#join method .

String joinedString = StringUtils.join(split, StringUtils.SPACE);

Which would produce "HE LL OW OR LD" .

So an all in one method would be:

public static String separateNthCharacter(String input, int len) {
    // To prevent any NullPointerException being thrown
    if (StringUtils.isEmpty()) {
        return StringUtils.EMPTY;
    }

    String[] split = input.split(String.format("(?<=\\G.{%1$d})", len));
    return StringUtils.join(split, StringUtils.SPACE);
}