Parser.java

package baseball.utils;

public class Parser {

        public int[] parseUserInput(String input, int size) throws IllegalArgumentException {
            checkSize(input, size);
            return getParseInt(input, size);
        }

        private void checkSize(String input, int size) throws IllegalArgumentException {
            if (input.length() != size) {
                throw new IllegalArgumentException();
            }
        }

        private int[] getParseInt(String input, int size) throws IllegalArgumentException {
            int[] parseInt = new int[size];

            for (int i = 0; i < input.length(); i++) {
                if (!checkDigit(input, i)) {
                    throw new IllegalArgumentException();
                }
                parseInt[i] = convertCharToInt(input, i);
            }
            return parseInt;
        }

        private int convertCharToInt(String input, int i) {
            return input.charAt(i) - '0';
        }

        private Boolean checkDigit(String input, int i) {
            return '0' <= input.charAt(i) && input.charAt(i) <= '9';
        }
    }