Refactor AtbashCipher, add ParameterizedTest

src/main/java/com/thealgorithms/ciphers/AtbashCipher.java

@@ -1,68 +1,98 @@
 package com.thealgorithms.ciphers;
 
 /**
- * The Atbash cipher is a simple substitution cipher that replaces each letter
- * in the alphabet with its reverse.
- * For example, 'A' becomes 'Z', 'B' becomes 'Y', and so on. It works
- * identically for both uppercase and lowercase letters.
- * It's a symmetric cipher, meaning applying it twice returns the original text.
- * Hence, the encrypting and the decrypting functions are identical
- * @author https://github.com/Krounosity
- * Learn more: https://en.wikipedia.org/wiki/Atbash
+ * The Atbash cipher is a classic substitution cipher that substitutes each letter
+ * with its opposite letter in the alphabet.
+ *
+ * For example:
+ * - 'A' becomes 'Z', 'B' becomes 'Y', 'C' becomes 'X', and so on.
+ * - Similarly, 'a' becomes 'z', 'b' becomes 'y', and so on.
+ *
+ * The cipher works identically for both uppercase and lowercase letters.
+ * Non-alphabetical characters remain unchanged in the output.
+ *
+ * This cipher is symmetric, meaning that applying the cipher twice will return
+ * the original text. Therefore, the same function is used for both encryption and decryption.
+ *
+ * <p>Usage Example:</p>
+ * <pre>
+ * AtbashCipher cipher = new AtbashCipher("Hello World!");
+ * String encrypted = cipher.convert(); // Output: "Svool Dliow!"
+ * </pre>
+ *
+ * @author <a href="https://github.com/Krounosity">Krounosity</a>
+ * @see <a href="https://en.wikipedia.org/wiki/Atbash">Atbash Cipher (Wikipedia)</a>
  */
-
 public class AtbashCipher {
 
     private String toConvert;
 
-    // Default constructor.
-    AtbashCipher() {
+    public AtbashCipher() {
     }
 
-    // String setting constructor.
-    AtbashCipher(String str) {
-        toConvert = str;
+    /**
+     * Constructor with a string parameter.
+     *
+     * @param str The string to be converted using the Atbash cipher
+     */
+    public AtbashCipher(String str) {
+        this.toConvert = str;
     }
 
-    // String getter method.
+    /**
+     * Returns the current string set for conversion.
+     *
+     * @return The string to be converted
+     */
     public String getString() {
         return toConvert;
     }
 
-    // String setter method.
+    /**
+     * Sets the string to be converted using the Atbash cipher.
+     *
+     * @param str The new string to convert
+     */
     public void setString(String str) {
-        toConvert = str;
+        this.toConvert = str;
     }
 
-    // Checking whether the current character is capital.
+    /**
+     * Checks if a character is uppercase.
+     *
+     * @param ch The character to check
+     * @return {@code true} if the character is uppercase, {@code false} otherwise
+     */
     private boolean isCapital(char ch) {
         return ch >= 'A' && ch <= 'Z';
     }
 
-    // Checking whether the current character is smallcased.
+    /**
+     * Checks if a character is lowercase.
+     *
+     * @param ch The character to check
+     * @return {@code true} if the character is lowercase, {@code false} otherwise
+     */
     private boolean isSmall(char ch) {
         return ch >= 'a' && ch <= 'z';
     }
 
-    // Converting text to atbash cipher code or vice versa.
+    /**
+     * Converts the input string using the Atbash cipher.
+     * Alphabetic characters are substituted with their opposite in the alphabet,
+     * while non-alphabetic characters remain unchanged.
+     *
+     * @return The converted string after applying the Atbash cipher
+     */
     public String convert() {
-
-        // Using StringBuilder to store new string.
         StringBuilder convertedString = new StringBuilder();
 
-        // Iterating for each character.
         for (char ch : toConvert.toCharArray()) {
-
-            // If the character is smallcased.
             if (isSmall(ch)) {
                 convertedString.append((char) ('z' - (ch - 'a')));
-            }
-            // If the character is capital cased.
-            else if (isCapital(ch)) {
+            } else if (isCapital(ch)) {
                 convertedString.append((char) ('Z' - (ch - 'A')));
-            }
-            // Non-alphabetical character.
-            else {
+            } else {
                 convertedString.append(ch);
             }
         }

src/test/java/com/thealgorithms/ciphers/AtbashTest.java

@@ -2,27 +2,42 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-import org.junit.jupiter.api.Test;
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 
 public class AtbashTest {
 
-    @Test
-    public void atbashEncrypt() {
-        AtbashCipher normalToEncrypt = new AtbashCipher("Hello World! 123, @cipher abcDEF ZYX 987 madam zzZ Palindrome!");
-        String expectedText = "Svool Dliow! 123, @xrksvi zyxWVU ABC 987 nzwzn aaA Kzormwilnv!";
+    @ParameterizedTest
+    @MethodSource("cipherTestProvider")
+    public void testAtbashCipher(String input, String expected) {
+        AtbashCipher cipher = new AtbashCipher(input);
+        assertEquals(expected, cipher.convert());
+    }
 
-        normalToEncrypt.setString(normalToEncrypt.convert());
+    private static Stream<Arguments> cipherTestProvider() {
+        return Stream.of(
+            // Basic tests with lowercase and uppercase
+            Arguments.of("Hello", "Svool"), Arguments.of("WORLD", "DLIOW"),
 
-        assertEquals(expectedText, normalToEncrypt.getString());
-    }
+            // Mixed case with spaces and punctuation
+            Arguments.of("Hello World!", "Svool Dliow!"), Arguments.of("123 ABC xyz", "123 ZYX cba"),
+
+            // Palindromes and mixed cases
+            Arguments.of("madam", "nzwzn"), Arguments.of("Palindrome", "Kzormwilnv"),
+
+            // Non-alphabetic characters should remain unchanged
+            Arguments.of("@cipher 123!", "@xrksvi 123!"), Arguments.of("no-change", "ml-xszmtv"),
 
-    @Test
-    public void atbashDecrypt() {
-        AtbashCipher encryptToNormal = new AtbashCipher("Svool Dliow! 123, @xrksvi zyxWVU ABC 987 nzwzn aaA Kzormwilnv!");
-        String expectedText = "Hello World! 123, @cipher abcDEF ZYX 987 madam zzZ Palindrome!";
+            // Empty string and single characters
+            Arguments.of("", ""), Arguments.of("A", "Z"), Arguments.of("z", "a"),
 
-        encryptToNormal.setString(encryptToNormal.convert());
+            // Numbers and symbols
+            Arguments.of("!@#123", "!@#123"),
 
-        assertEquals(expectedText, encryptToNormal.getString());
+            // Full sentence with uppercase, lowercase, symbols, and numbers
+            Arguments.of("Hello World! 123, @cipher abcDEF ZYX 987 madam zzZ Palindrome!", "Svool Dliow! 123, @xrksvi zyxWVU ABC 987 nzwzn aaA Kzormwilnv!"),
+            Arguments.of("Svool Dliow! 123, @xrksvi zyxWVU ABC 987 nzwzn aaA Kzormwilnv!", "Hello World! 123, @cipher abcDEF ZYX 987 madam zzZ Palindrome!"));
     }
 }