feat: demonstrate conversion of String to StringBuffer and StringBuilder with operations

WHAT was added:
- Implemented `StringConversion` class to show interoperability between `String`, `StringBuffer`, and `StringBuilder`.
- Converted a `String` ("Geeks") into:
  - `StringBuffer` → used `reverse()` to showcase mutability and modification in place.
  - `StringBuilder` → used `append("forGeeks")` to demonstrate efficient concatenation.

WHY this matters:
- Emphasizes that while `String` is immutable, both `StringBuffer` and `StringBuilder` are mutable.
- Demonstrates how existing `String` data can be wrapped in mutable alternatives for efficient modifications.

PROGRAM OUTPUT:
- `skeeG` (reversed using `StringBuffer`)
- `GeeksforGeeks` (appended using `StringBuilder`)

REAL-WORLD APPLICATIONS:
- **StringBuffer reverse()** → used in algorithms like palindrome checkers, cryptography, or text editors where reversing is needed.
- **StringBuilder append()** → ideal for building large dynamic strings (e.g., SQL queries, JSON/XML builders, log messages).
- **Conversion** → allows starting with immutable `String` (safe input) and switching to mutable types for processing.

KEY TAKEAWAYS:
1. `StringBuffer` and `StringBuilder` constructors accept a `String` for easy conversion.
2. `StringBuffer` is synchronized → thread-safe but slower.
3. `StringBuilder` is non-synchronized → faster in single-threaded contexts.
4. Choose based on performance vs. concurrency needs.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section20JAVA.lang.Package/src/StringConversion.java

@@ -1,29 +1,41 @@
-// Java program to demonstrate conversion from
-// String to StringBuffer and StringBuilder
 public class StringConversion {
-
     public static void main(String[] args) {
-
-        // Custom input string
         String s = "Geeks";
 
-        // Converting String object to StringBuffer object
-        // by creating object of StringBuffer class
+        // Converting String object to StringBuffer object by creating an object of StringBuffer class.
         StringBuffer sbr = new StringBuffer(s);
 
-        // Reversing the string
+        // Reversing the string.
         sbr.reverse();
-
-        // Printing the reversed string
         System.out.println(sbr);
 
-        // Converting String object to StringBuilder object
+        // Converting String object to StringBuilder object.
         StringBuilder sbl = new StringBuilder(s);
 
-        // Adding it to string using append() method
+        // Adding it to string using append() method.
         sbl.append("forGeeks");
 
-        // Print and display the above appended string
+        // Print and display the above appended string.
         System.out.println(sbl);
     }
 }
+
+/*  Java program to demonstrate conversion from String to StringBuffer and StringBuilder.
+
+1. String → Immutable (once created, modify nahi hota).
+   Example: "Geeks" me kuch bhi add/modify karoge to new String object banega.
+
+2. StringBuffer → Mutable + Thread-safe
+   - Isliye reverse(), append(), insert(), delete() directly existing object pe kaam karte hain.
+
+3. StringBuilder → Mutable + Faster (NOT synchronized)
+   - Single-threaded applications me zyada fast hota hai.
+
+4. Conversions:
+   - String → StringBuffer:  new StringBuffer(s)
+   - String → StringBuilder: new StringBuilder(s)
+
+5. Example Output:
+   - Reversed StringBuffer: skeeG
+   - Appended StringBuilder: GeeksforGeeks
+*/