Example: Array Reversal using Recursion in Java

// Array Reversal using Recursion
import java.util.Arrays; // Required for printing the array easily

// Main class containing the entry point of the program
public class Main {

    // Recursive function to reverse an array
    public static void reverseArrayRecursive(int[] arr, int start, int end) {
        // Step 1: Base Case - If start index is greater than or equal to end index,
        // it means the sub-array has one or zero elements, or we've crossed over,
        // so no more swaps are needed.
        if (start >= end) {
            return;
        }

        // Step 2: Swap elements at the start and end positions
        int temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;

        // Step 3: Recursive Call - Call the function for the sub-array
        // by incrementing start and decrementing end, moving inwards.
        reverseArrayRecursive(arr, start + 1, end - 1);
    }

    public static void main(String[] args) {
        // Step 1: Initialize an array
        int[] numbers = {10, 20, 30, 40, 50, 60};

        // Step 2: Print the original array
        System.out.println("Original Array: " + Arrays.toString(numbers));

        // Step 3: Call the recursive function to reverse the array
        // The initial call uses 0 as start index and length-1 as end index.
        reverseArrayRecursive(numbers, 0, numbers.length - 1);

        // Step 4: Print the reversed array
        System.out.println("Reversed Array: " + Arrays.toString(numbers));

        // Test with an array of odd length
        int[] oddNumbers = {1, 2, 3, 4, 5};
        System.out.println("\nOriginal Odd Length Array: " + Arrays.toString(oddNumbers));
        reverseArrayRecursive(oddNumbers, 0, oddNumbers.length - 1);
        System.out.println("Reversed Odd Length Array: " + Arrays.toString(oddNumbers));
    }
}