feat: Add regex-based check to validate hexadecimal number format

- Implements a simple Java program to check if a given string is a valid hexadecimal number.
- Uses the regular expression `[0-9A-F]*` to match any string composed solely of hexadecimal characters.
  - `[0-9A-F]` matches any digit (0–9) or uppercase letter A–F (representing values 10–15).
  - `*` quantifier allows zero or more such characters (use `+` to require at least one).
- Example used: "234AB" — a valid hexadecimal number, so the output is `true`.

📝 Notes:
- This validation assumes uppercase hex letters. To handle lowercase or mixed case, use `[0-9A-Fa-f]*`.
- Hexadecimal numbers are widely used in computing, often for memory addresses, color codes, etc.

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

Author: Someshdiwan

Section6StringClassPrinting/src/RegularExpressionChallenge1.java

@@ -1,14 +1,15 @@
 //Find is number is hexa decimal or not
 //[0-9A-F]+ plus is they are one or more
 
-public class RegularExpressionChallenge1
-{
-    public static void main(String[] args)
-    {
+public class RegularExpressionChallenge1 {
+    public static void main(String[] args) {
         String str = "234AB";
         System.out.println(str.matches("[0-9A-F]*"));
-
-        //The hexadecimal number system, often referred to as "hex," is a base-16 numeral system used extensively in computing and digital electronics.
-        //It consists of 16 symbols: the numbers 0 to 9 and the letters A to F. These letters represent the decimal values 10 to 15, respectively
+        /*
+        The hexadecimal number system, often referred to as "hex," is a base-16 numeral system used extensively in
+        computing and digital electronics.
+        It consists of 16 symbols: the numbers 0 to 9 and the letters A to F.
+        These letters represent the decimal values 10 to 15, respectively
+        */
     }
-}
+}