feat: Remove special characters from a string using regex

- Input: String containing mixed characters including letters, digits, and special symbols (e.g., "a!B@c#1$2%3")
- Applied regex pattern `[^a-zA-Z0-9]` with `replaceAll()` method to remove all characters *except*:
  - Lowercase letters (a–z)
  - Uppercase letters (A–Z)
  - Digits (0–9)
- Replaced disallowed characters with a space to retain readability.

🔍 Explanation:
- `[^a-zA-Z0-9]` is a negated character class, meaning it matches any character *not* in the allowed ranges.
- Useful for sanitizing user input, cleaning noisy strings, or preparing data for processing.

🧪 Example:
- Input: `a!B@c#1$2%3`
- Output: `a B c 1 2 3`

Signed-off-by: Somesh diwan <[email protected]>

Author: Someshdiwan

Section6StringClassPrinting/src/RegularExpressionChallenge3.java

@@ -1,3 +1,11 @@
+class RegularExpressionChallange3 {
+    public static void main(String[] args) {
+        String str = "a!B@c#1$2%3";
+
+        System.out.println(str.replaceAll("[^a-zA-Z0-9]", " "));
+    }
+}
+
 /*
 Remove Special Characters from a String
 
@@ -6,13 +14,3 @@
 method called str.replace() and str.replaceAll()
 what is allowed is [^a-zA-Z0-9] use symbol not ^ if not among this.
 */
-
-class RegularExpressionChallange3
-{
-    public static void main(String[] args)
-    {
-        String str = "a!B@c#1$2%3";
-
-        System.out.println(str.replaceAll("[^a-zA-Z0-9]", " "));
-    }
-}