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));
     }
 }

src/test/java/com/thealgorithms/strings/AlphabeticalTest.java

@@ -1,30 +1,15 @@
 package com.thealgorithms.strings;
 
-import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 public class AlphabeticalTest {
 
-    @Test
-    public void isAlphabetical() {
-        // expected to be true
-        String input1 = "abcdefghijklmno";
-        String input2 = "abcdxxxyzzzz";
-        String input3 = "fpw";
-
-        // expected to be false
-        String input4 = "123a";
-        String input5 = "abcABC";
-        String input6 = "abcdefghikjlmno";
-
-        assertTrue(Alphabetical.isAlphabetical(input1));
-        assertTrue(Alphabetical.isAlphabetical(input2));
-        assertTrue(Alphabetical.isAlphabetical(input3));
-
-        assertFalse(Alphabetical.isAlphabetical(input4));
-        assertFalse(Alphabetical.isAlphabetical(input5));
-        assertFalse(Alphabetical.isAlphabetical(input6));
+    @ParameterizedTest(name = "\"{0}\" → Expected: {1}")
+    @CsvSource({"'abcdefghijklmno', true", "'abcdxxxyzzzz', true", "'123a', false", "'abcABC', false", "'abcdefghikjlmno', false", "'aBC', true", "'abc', true", "'xyzabc', false", "'abcxyz', true", "'', false", "'1', false"})
+    void testIsAlphabetical(String input, boolean expected) {
+        assertEquals(expected, Alphabetical.isAlphabetical(input));
     }
 }