feat(ListDemo4): demonstrate List to array conversion and sorting

What
- Added ListDemo4 example.
- Showed two ways to convert a `List<Integer>` to arrays:
  1. `toArray()` → returns `Object[]`.
  2. `toArray(new Integer[0])` → returns a typed `Integer[]`.
- Printed the array reference (default `toString()` prints memory address).
- Sorted the list using `Collections.sort()` and printed the result.

Why
- Clarifies difference between `toArray()` overloads.
- Shows best practice: using `toArray(new Integer[0])` for type safety.
- Reinforces usage of `Collections.sort()` for natural ordering.

How
- Create `ArrayList<Integer>` with elements [5,1,2,3].
- Convert list to `Object[]` and `Integer[]`.
- Print `array1` (prints reference, not values).
- Sort list ascending → [1,2,3,5].
- Print sorted list.

Logic
- `Object[] array = list.toArray();`
  - Produces a generic array of type Object[].
- `Integer[] array1 = list.toArray(new Integer[0]);`
  - Produces a strongly typed Integer[].
  - Common idiom: passing zero-length array ensures correct type.
- Sorting:
  - `Collections.sort(list);` → O(n log n) using TimSort.
  - Natural ordering: ascending for integers.

Real-life applications
- Exporting collections to arrays for interoperability with legacy APIs.
- Ensuring type safety when working with arrays from generics.
- Sorting lists in-place for display, storage, or computation.

Notes
- Printing an array directly (`System.out.println(array1)`) prints its memory address.
  Use `Arrays.toString(array1)` for human-readable output.
- `Collections.sort(list)` modifies list in place.
- Since Java 8, you can also use `list.sort(null)` for natural ordering.

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

Author: Someshdiwan

Section 25 Collections Frameworks/List Interface/ArrayList/src/ListDemo4.java

@@ -0,0 +1,23 @@
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class ListDemo4 {
+    public static void main(String[] args) {
+        List<Integer> list = new ArrayList<>();
+
+        list.add(5);
+        list.add(1);
+        list.add(2);
+        list.add(3);
+
+        // List to array.
+        Object[] array = list.toArray();
+        Integer[] array1 = list.toArray(new Integer[0]); // Zero Size Ki Array.
+        System.out.println(array1);
+
+        // Sort the list.
+        Collections.sort(list);
+        System.out.println(list);
+    }
+}