feat(ListDemo1): add demo of converting List to arrays (Object[] and typed Integer[])

What
- Added ListDemo1 class.
- Created a List<Integer> with values [1,2,3].
- Demonstrated two methods of converting List to array:
  - toArray() → returns Object[].
  - toArray(new Integer[0]) → returns typed Integer[].
- Printed both arrays to verify conversion.

Why
- Highlights difference between raw toArray() and generic toArray(T[]).
- Shows why using toArray(new T[0]) is preferred to avoid casting from Object[].
- Provides a clear example of converting a generic collection to arrays.

How
- list = [1,2,3].
- Object[] objectArray = list.toArray():
  - Produces array of type Object[].
  - Iterated and printed as Objects.
- Integer[] integerArray = list.toArray(new Integer[0]):
  - Produces array of type Integer[].
  - Iterated and printed as Integers.

Logic
- Inputs: integers added to ArrayList.
- Outputs: elements printed from both Object[] and Integer[] arrays.
- Flow:
  1. Create list and add elements.
  2. Convert to Object[] via toArray().
  3. Iterate and print.
  4. Convert to Integer[] via toArray(new Integer[0]).
  5. Iterate and print.
- Edge cases:
  - toArray() returns Object[] → requires explicit casting if assigning to specific type.
  - toArray(new Integer[size]) also works (slightly faster than new Integer[0]).
- Complexity: O(n) copy for toArray().
- Concurrency: not thread-safe.

Real-life applications
- Converting lists into arrays for APIs that require arrays (e.g., legacy libraries, JDBC batch parameters).
- Typed array conversions useful for serialization, reflection, or exporting data.
- Object[] variant useful when type safety not required.

Notes
- Best practice is to use toArray(new T[0]) to get strongly-typed arrays.
- In Java 11+, toArray(IntFunction<T[]>) is available for even more concise conversions.

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

Author: Someshdiwan

Section 25 Collections Frameworks/List Interface/ArrayList/src/ListDemo1.java

@@ -0,0 +1,33 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class ListDemo1 {
+    public static void main(String[] args) {
+        List<Integer> list = new ArrayList<>();
+        list.add(1);
+        list.add(2);
+        list.add(3);
+
+        System.out.println(list);
+
+        // Method 1: Convert List to an Object array.
+        // The toArray() method without arguments returns an Object[] because it does not know the specific type.
+        Object[] objectArray = list.toArray();
+
+        System.out.println("Object array:");
+
+        for (Object obj : objectArray) {
+            System.out.println(obj);
+        }
+
+        // Method 2: Convert List to a typed Integer array.
+        // By passing an array of the desired type (new Integer[0]), the method returns an array of type Integer[].
+        Integer[] integerArray = list.toArray(new Integer[0]);
+
+        System.out.println("\nInteger array:");
+
+        for (Integer num : integerArray) {
+            System.out.println(num);
+        }
+    }
+}