feat: add example demonstrating @deprecated and @SuppressWarnings annotations

WHAT was added:
- Created `OldClass` with:
  - `display()` method (normal, not deprecated).
  - `show()` method marked with `@Deprecated` to indicate it should not be used in new code.
- Created `Annotations` class with a `main` method:
  - Calls `show()` while suppressing compiler warnings using `@SuppressWarnings("deprecation")`.

KEY LEARNINGS:
1. @deprecated:
   - Marks a method, class, or field as obsolete or unsafe to use.
   - Compiler generates a warning when the deprecated element is used.
   - Often used when APIs are replaced by newer versions but kept for backward compatibility.

2. @SuppressWarnings("deprecation"):
   - Suppresses warnings triggered by using deprecated APIs.
   - Should be used sparingly and only when you understand the implications.
   - Example: maintaining legacy code while avoiding unnecessary compiler noise.

3. Best Practices:
   - Prefer new methods over deprecated ones whenever possible.
   - Document why suppression is necessary if you use `@SuppressWarnings`.

REAL-WORLD APPLICATIONS:
- ✅ Migrating legacy code: `@Deprecated` helps signal outdated APIs.
- ✅ Backward compatibility: Older methods remain available but marked as discouraged.
- ✅ Clean build pipelines: `@SuppressWarnings` avoids unnecessary warnings in stable legacy code.
- ✅ API evolution: Libraries like Spring, Java SDK, Android SDK use `@Deprecated` to phase out old methods gracefully.

RULE OF THUMB:
- Use `@Deprecated` to communicate API evolution to developers.
- Use `@SuppressWarnings` only when absolutely necessary, with clear documentation.
- Always migrate to newer APIs in the long run for better performance and maintainability.

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

Author: Someshdiwan

Section21AnnotationsandJavaDoc/src/Annotations.java

@@ -16,3 +16,25 @@ public static void main(String[] args) {
         o.show(); //Deprecated Method
     }
 }
+
+/*
+1. @Deprecated
+   - Jab kisi method/class ko future me use na karne ki recommendation hoti hai
+     to usse @Deprecated mark karte hain.
+   - Compiler warning deta hai ki ye method "old" hai aur avoid karna chahiye.
+   - Example: o.show() ek deprecated method hai.
+
+2. @SuppressWarnings("deprecation")
+   - Jab tum intentionally deprecated method ko use karna chahte ho
+     aur warning avoid karni hai, to ye annotation use karte ho.
+   - Sirf warning suppress hoti hai, code chalna continue karega.
+
+3. Is example me:
+   - `OldClass` ke andar `show()` ko deprecated mark kiya gaya.
+   - `main()` me use call kiya gaya, but warning suppress karne ke liye
+     @SuppressWarnings("deprecation") lagaya gaya.
+
+4. Use Case:
+   - Jab purane APIs ya libraries use kar rahe ho lekin abhi migrate nahi kar pa rahe,
+     to warnings avoid karne ke liye ye annotation lagate ho.
+*/