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- ✅ Migrating legacy code: `@Deprecated` helps signal outdated APIs.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

@@ -1,45 +1,15 @@
-
-/*abstract class Parent1{
-    abstract public void display();
-}
-
-class Child extends Parent1
-{
-    public void display() //Abstract method overriding a method.
-    {
-
-    }
-}*/
-
-/*class Parent{
-    public void display(){}
-}
-class Child extends Parent
-{
-    //To avoid this type of silly Mistake use Annotations.
-    @Override
-    public void display(){
-
-    }
-}*/
-
-
-
-class OldClass
-{
-    public void display()
-    {
+class OldClass {
+    public void display() {
         System.out.println("Hello");
     }
+
     @Deprecated
-    public void show()
-    {
+    public void show() {
         System.out.println("Hi");
     }
 }
 
-public class Annotations
-{
+public class Annotations {
     @SuppressWarnings("deprecation")
     public static void main(String[] args) {
         OldClass o=new OldClass();