feat: demonstrate enum declaration inside and outside a class in Java

WHAT was added:
- Created a global enum `Color { RED, GREEN, BLUE }` and used it in `Enum3`.
- Demonstrated declaring an enum *inside* a class (`Enum4`) and using it similarly.
- Printed enum constants to show usage.

WHY this matters:
- Enums in Java can be declared at **top-level** (outside classes) or as **nested types** (inside a class).
- Helps developers understand valid scopes for enums:
  - Outside any class (global scope).
  - Inside a class (nested enum).
  - Not allowed inside a method.

HOW it works:
- `Enum3` uses a globally declared enum `Color`.
- `Enum4` declares its own nested `Color` enum and references it within `main()`.
- Both approaches allow constants to be accessed as `Color.RED`.

REAL-LIFE APPLICATIONS:
- Top-level enums → shared across packages, e.g., `Status { PENDING, RUNNING, COMPLETED }`.
- Nested enums → tied to a specific class context, e.g.:
  - `Order.State { NEW, PROCESSING, DELIVERED }` inside `Order` class.
  - `TrafficLight.Color { RED, YELLOW, GREEN }` inside `TrafficLight` class.

NOTES / BEST PRACTICES:
1. Enum constants are implicitly `public static final`.
2. Enums should be named in singular form (`Color` instead of `Colors`).
3. Constants should follow UPPERCASE naming convention (`RED, GREEN, BLUE`).
4. Avoid declaring enums inside methods — this is not supported in Java.
5. Use top-level enums when they are reused widely, and nested enums when they are strongly coupled to a single class.

KEYWORDS:
enum, nested enum, top-level enum, declaration rules, type-safe constants.

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

Author: Someshdiwan

Section20JAVA.lang.Package/src/Enum3.java

@@ -1,34 +1,50 @@
-/*
-Enum declaration can be done outside a class or inside a class but not inside a method.
- A simple enum example where enum is declared
- outside any class (Note enum keyword instead of
- class keyword)
- */
 enum Color {
     RED,
     GREEN,
     BLUE;
 }
+
 public class Enum3 {
-    // Driver method
     public static void main(String[] args) {
         Color c1 = Color.RED;
         System.out.println(c1);
     }
 }
 
 // enum declaration inside a class.
-class Enum4 extends Enum3
-{
-    enum Color
-    {
+class Enum4 extends Enum3 {
+    enum Color {
         RED,
         GREEN,
         BLUE;
     }
-    // Driver method
     public static void main(String[] args) {
         Color c1 = Color.RED;
         System.out.println(c1);
     }
-}
+}
+
+/*
+Enum declaration rules:
+1. Enum ko class ke bahar ya class ke andar declare kar sakte ho.
+2. Lekin enum ko method ke andar declare nahi kar sakte.
+3. enum keyword use karte ho (class keyword ki jagah).
+
+1. Enum bahar bhi declare kar sakte ho (global scope)
+   → "enum Color { ... }" outside any class.
+
+2. Enum class ke andar bhi declare kar sakte ho
+   → "class Enum4 { enum Color { ... } }"
+
+3. Enum method ke andar declare.(not allowed).
+
+4. Enum constants by default public, static, final hote hain.
+   Isliye direct access: Color.RED
+
+5. Best practice:
+   - Enum names → singular (Color not Colors).
+   - Constants → UPPERCASE (RED, GREEN, BLUE).
+
+Enum declaration can be done outside a class or inside a class but not inside a method.
+A simple enum example where enum is declared outside any class (Note enum keyword instead of class keyword).
+*/