feat: demonstrate type safety with Java Generics vs raw ArrayList usage

WHAT:
- Added `Main.java` to show safe usage of `ArrayList<String>` with Generics.
- Added `Main2.java` to illustrate potential runtime issues when using a raw `ArrayList` without Generics.

HOW:
1. `Main.java`:
   - Created an `ArrayList<String>` to store only `String` values.
   - Type safety enforced at compile-time; retrieving elements does not require casting.
   - Example: `list.get(0)` directly returns a `String`.

2. `Main2.java`:
   - Created a raw `ArrayList` (no type parameter).
   - Mixed data types inserted: `String`, `Integer`, `Double`.
   - Explicit casting required when retrieving elements.
   - Demonstrates risk of `ClassCastException` at runtime (e.g., trying to cast an `Integer` to `String`).

WHY:
- Highlights the importance of **Generics** in Java collections.
- Generics provide compile-time type safety and eliminate the need for manual casting.
- Without Generics (raw types), type mismatches are only detected at runtime, leading to potential crashes.

REAL-WORLD APPLICATIONS:
- Generics are widely used in collections (`List<T>`, `Map<K,V>`, `Set<T>`) to ensure data consistency.
- Useful in frameworks (Spring, Hibernate) to enforce strong typing.
- Prevents runtime errors in large codebases by catching type mismatches during compilation.

NOTES:
- `Main2` will throw `ClassCastException` when attempting `String str1 = (String) list.get(1);`
  because the second element is actually an `Integer`.
- Best practice: always use parameterized collections with Generics instead of raw types.

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

Author: Someshdiwan

Section24JavaGenerics/src/Generics/Main.java

@@ -0,0 +1,23 @@
+package Generics;
+
+import java.util.ArrayList;
+
+public class Main {
+    public static void main(String[] args) {
+        ArrayList<String> list = new ArrayList<>();
+        list.add("Hello");
+        list.add("World");
+        String s = list.get(0);
+        String s1 = list.get(1);
+
+    }
+}
+
+/*
+The above code issues solved by Generics:
+
+No Type safety
+Manual casting
+No Compile Time checking
+Generics can solve These issues.
+*/

Section24JavaGenerics/src/Generics/Main2.java

@@ -0,0 +1,23 @@
+package Generics;
+
+import java.util.ArrayList;
+
+public class Main2 {
+    public static void main(String[] args) {
+        ArrayList list = new ArrayList();
+        list.add("Hello");
+        list.add(123);
+        list.add(3.14);
+
+        String str = (String) list.get(0);
+        String str1 = (String) list.get(1);
+    }
+}
+
+/*
+Above code has 3 major issues:
+No Type safety
+Manual casting
+No Compile Time checking
+Generics can solve These issues. check code Main.
+*/