refactor: refactor Alphabetical and AlphabeticalTest (#6355)

src/main/java/com/thealgorithms/strings/Alphabetical.java

@@ -1,36 +1,32 @@
 package com.thealgorithms.strings;
 
 /**
+ * Utility class for checking if a string's characters are in alphabetical order.
+ * <p>
  * 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
+ * alphabet.
+ * <p>
+ * Reference: <a href="https://en.wikipedia.org/wiki/Alphabetical_order">Wikipedia: Alphabetical Order</a>
  */
-final class Alphabetical {
+public final class Alphabetical {
     private 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
+     * Checks whether the characters in the given string are in alphabetical order.
+     * Non-letter characters will cause the check to fail.
      *
-     * @param s a string
-     * @return {@code true} if given string is alphabetical order, otherwise
-     * {@code false}
+     * @param s the input string
+     * @return {@code true} if all characters are in alphabetical order (case-insensitive), 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))) {
+            if (!Character.isLetter(s.charAt(i)) || s.charAt(i) > s.charAt(i + 1)) {
                 return false;
             }
         }
-        return true;
+        return !s.isEmpty() && Character.isLetter(s.charAt(s.length() - 1));
     }
 }