diff --git a/src/main/java/com/ctci/arraysandstrings/IsUnique.java b/src/main/java/com/ctci/arraysandstrings/IsUnique.java
index 895d16b3..e509102f 100644
--- a/src/main/java/com/ctci/arraysandstrings/IsUnique.java
+++ b/src/main/java/com/ctci/arraysandstrings/IsUnique.java
@@ -1,21 +1,62 @@
 package com.ctci.arraysandstrings;
 
+import java.util.HashSet;
+import java.util.Set;
+
 /**
  * @author rampatra
  * @since 18/11/2018
  */
 public class IsUnique {
 
-    private static boolean hasAllUniqueCharacters(String str) {
-        if (str == null || str.length() > 128) return false;
+    /**
+     * Check whether the input string contains different individual characters in the ASCII table.
+     *
+     * @param inputString Input string
+     * @return true if all characters are different from each other, otherwise false.
+     */
+    public static boolean hasDifferentIndividualCharacters(String inputString) {
+        int  maxCharacterDecimal = 128;
+
+        if (inputString == null
+                || inputString.isEmpty()
+                || inputString.length() > maxCharacterDecimal) {
+            return false;
+        }
+
+        boolean[] characterTrack = new boolean[maxCharacterDecimal];
+
+        int inputStringLength = inputString.length();
+        for (int i = 0; i < inputStringLength; i++) {
+            int charInDecimal = inputString.charAt(i);
+
+            if (charInDecimal >= maxCharacterDecimal
+                    || characterTrack[charInDecimal]) {
+                return false;
+            }
+
+            characterTrack[charInDecimal] = true;
+        }
+        return true;
+    }
+
+    /**
+     * Check whether the input string contains different individual characters.
+     *
+     * @param inputString Input string
+     * @return true if all characters are different from each other, otherwise false.
+     */
+    public static boolean hasAllUniqueCharactersEnhancement(String inputString) {
+        if (inputString == null || inputString.isEmpty()) {
+            return false;
+        }
 
-        boolean[] charSet = new boolean[128]; // assuming the string contains only ASCII characters
-        for (int i = 0; i < str.length(); i++) {
-            int charVal = str.charAt(i);
-            if (charSet[charVal]) {
+        Set<Character> charSet = new HashSet<>();
+        char[] inputStingArr = inputString.toCharArray();
+        for (char c : inputStingArr) {
+            if (!charSet.add(c)) {
                 return false;
             }
-            charSet[charVal] = true;
         }
         return true;
     }
@@ -34,11 +75,11 @@ private static boolean hasAllUniqueCharactersWhenStringContainsAllLowercase(Stri
 
     public static void main(String[] args) {
         String s = "ram";
-        System.out.println(hasAllUniqueCharacters(s));
+        System.out.println(hasDifferentIndividualCharacters(s));
         s = "rama";
-        System.out.println(hasAllUniqueCharacters(s));
+        System.out.println(hasDifferentIndividualCharacters(s));
         s = "ramA";
-        System.out.println(hasAllUniqueCharacters(s));
+        System.out.println(hasDifferentIndividualCharacters(s));
         System.out.println("-------");
         s = "ram";
         System.out.println(hasAllUniqueCharactersWhenStringContainsAllLowercase(s));
diff --git a/src/main/java/com/ctci/arraysandstrings/IsUniqueTest.java b/src/main/java/com/ctci/arraysandstrings/IsUniqueTest.java
new file mode 100644
index 00000000..280f57f3
--- /dev/null
+++ b/src/main/java/com/ctci/arraysandstrings/IsUniqueTest.java
@@ -0,0 +1,112 @@
+package com.ctci.arraysandstrings;
+
+import org.junit.jupiter.api.*;
+
+public class IsUniqueTest {
+
+    @Nested
+    @DisplayName("Test cases for hasDifferentIndividualCharacters() method")
+    class TestCasesForHasDifferentIndividualCharacters {
+
+        @Test
+        public void testHasDifferentIndividualCharacters_StringIsNull_ReturnFalse() {
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters(null));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_StringIsEmpty_ReturnFalse() {
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters(""));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_StringLengthSmallerOrEqual128_ReturnFalse() {
+            StringBuilder stringBuilder = new StringBuilder();
+
+            for (int i = 0; i < 128; i++) {
+                stringBuilder.append((char) i);
+            }
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters(stringBuilder.toString()));
+
+            stringBuilder.setLength(0);
+            for (int i = 1; i < 127; i++) {
+                stringBuilder.append((char) i);
+            }
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters(stringBuilder.toString()));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_StringLengthLargerThan128_ReturnFalse() {
+            StringBuilder stringBuilder = new StringBuilder();
+
+            for (int i = 0; i < 128; i++) {
+                stringBuilder.append((char) i);
+            }
+            stringBuilder.append("a");
+
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters(stringBuilder.toString()));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_DuplicateAtHead_ReturnFalse() {
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("aab"));
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("AAb"));
+
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("ááb"));
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("ÁÁb"));
+
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("1123456"));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_DuplicateAtMiddle_ReturnFalse() {
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("abcbd"));
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("aBcBd"));
+
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("aưcưd"));
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("aƯcƯd"));
+
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("123436"));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_DuplicateAtTail_ReturnFalse() {
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("aba"));
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("AbA"));
+
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("ăbă"));
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("ĂbĂ"));
+
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("1234566"));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_OnlyOneCharacter_ReturnTrue() {
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters("a"));
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters("1"));
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters("A"));
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters("#"));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_OnlyOneCharacter_ReturnFalse() {
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("á"));
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("Ô"));
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("€"));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_InvalidString_ReturnFalse() {
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("ۇ"));
+            Assertions.assertFalse(IsUnique.hasDifferentIndividualCharacters("áÂ"));
+        }
+
+        @Test
+        public void testHasDifferentIndividualCharacters_ValidString_ReturnTrue() {
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters("aAb"));
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters("abcBd"));
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters("abA"));
+            Assertions.assertTrue(IsUnique.hasDifferentIndividualCharacters(
+                    "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"));
+        }
+    }
+}
\ No newline at end of file