refactor: HammingDistance (#5404)

* refactor: HammingDistance

* checkstyle: fix formatting

---------

Co-authored-by: alxkm <alx@alx.com>

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

@@ -1,34 +1,45 @@
 package com.thealgorithms.strings;
 
-/* In information theory, the Hamming distance between two strings of equal length
-is the number of positions at which the corresponding symbols are different.
-https://en.wikipedia.org/wiki/Hamming_distance
+/**
+ * Class for calculating the Hamming distance between two strings of equal length.
+ * <p>
+ * The Hamming distance is the number of positions at which the corresponding symbols are different.
+ * It is used in information theory, coding theory, and computer science.
+ * </p>
+ * @see <a href="https://en.wikipedia.org/wiki/Hamming_distance">Hamming distance - Wikipedia</a>
  */
 public final class HammingDistance {
     private HammingDistance() {
     }
 
     /**
-     * calculate the hamming distance between two strings of equal length
+     * Calculates the Hamming distance between two strings of equal length.
+     * <p>
+     * The Hamming distance is defined only for strings of equal length. If the strings are not
+     * of equal length, this method throws an {@code IllegalArgumentException}.
+     * </p>
      *
      * @param s1 the first string
      * @param s2 the second string
-     * @return {@code int} hamming distance
-     * @throws Exception
+     * @return the Hamming distance between the two strings
+     * @throws IllegalArgumentException if the lengths of {@code s1} and {@code s2} are not equal
      */
-    public static int calculateHammingDistance(String s1, String s2) throws Exception {
+    public static int calculateHammingDistance(String s1, String s2) {
+        if (s1 == null || s2 == null) {
+            throw new IllegalArgumentException("Strings must not be null");
+        }
+
         if (s1.length() != s2.length()) {
-            throw new Exception("String lengths must be equal");
+            throw new IllegalArgumentException("String lengths must be equal");
         }
 
-        int stringLength = s1.length();
-        int counter = 0;
+        int distance = 0;
 
-        for (int i = 0; i < stringLength; i++) {
+        for (int i = 0; i < s1.length(); i++) {
             if (s1.charAt(i) != s2.charAt(i)) {
-                counter++;
+                distance++;
             }
         }
-        return counter;
+        return distance;
     }
 }

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

@@ -3,22 +3,34 @@ package com.thealgorithms.strings;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
+import java.util.stream.Stream;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.CsvSource;
+import org.junit.jupiter.params.provider.MethodSource;
 
-public class HammingDistanceTest {
+class HammingDistanceTest {
 
-    @Test
-    void testHammingDistance() throws Exception {
-        assertEquals(HammingDistance.calculateHammingDistance("", ""), 0);
-        assertEquals(HammingDistance.calculateHammingDistance("java", "java"), 0);
-        assertEquals(HammingDistance.calculateHammingDistance("karolin", "kathrin"), 3);
-        assertEquals(HammingDistance.calculateHammingDistance("kathrin", "kerstin"), 4);
-        assertEquals(HammingDistance.calculateHammingDistance("00000", "11111"), 5);
+    @ParameterizedTest
+    @CsvSource({"'', '', 0", "'java', 'java', 0", "'karolin', 'kathrin', 3", "'kathrin', 'kerstin', 4", "'00000', '11111', 5", "'10101', '10100', 1"})
+    void testHammingDistance(String s1, String s2, int expected) {
+        assertEquals(expected, HammingDistance.calculateHammingDistance(s1, s2));
+    }
+
+    @ParameterizedTest
+    @MethodSource("provideNullInputs")
+    void testHammingDistanceWithNullInputs(String input1, String input2) {
+        assertThrows(IllegalArgumentException.class, () -> HammingDistance.calculateHammingDistance(input1, input2));
+    }
+
+    private static Stream<Arguments> provideNullInputs() {
+        return Stream.of(Arguments.of(null, "abc"), Arguments.of("abc", null), Arguments.of(null, null));
     }
 
     @Test
     void testNotEqualStringLengths() {
-        Exception exception = assertThrows(Exception.class, () -> HammingDistance.calculateHammingDistance("ab", "abc"));
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> HammingDistance.calculateHammingDistance("ab", "abc"));
         assertEquals("String lengths must be equal", exception.getMessage());
     }
 }