Alphabetical.java

package com.thealgorithms.strings;

/**
 * Alphabetical order is a system whereby character strings are placed in order
 * based on the position of the characters in the conventional ordering of an
 * alphabet. Wikipedia: https://en.wikipedia.org/wiki/Alphabetical_order
 */
class Alphabetical {

    public static void main(String[] args) {
        assert !isAlphabetical("123abc");
        assert isAlphabetical("aBC");
        assert isAlphabetical("abc");
        assert !isAlphabetical("xyzabc");
        assert isAlphabetical("abcxyz");
    }

    /**
     * Check if a string is alphabetical order or not
     *
     * @param s a string
     * @return {@code true} if given string is alphabetical order, otherwise
     * {@code false}
     */
    public static boolean isAlphabetical(String s) {
        s = s.toLowerCase();
        for (int i = 0; i < s.length() - 1; ++i) {
            if (!Character.isLetter(s.charAt(i)) || !(s.charAt(i) <= s.charAt(i + 1))) {
                return false;
            }
        }
        return true;
    }
}