Write a Java program to reverse an array.

This program reverses an array in-place and prints both the original and the reversed arrays. Here’s how it works:

class Main {
    public static void main(String[] args) {
        int[] arr = {1, 5, 2, 5, 7};
        
        // Print the original array
        System.out.print("Original array: ");
        printArr(arr);
        
        // Reverse the array
        revArr(arr);
        
        // Print the reversed array
        System.out.print("Reversed array: ");
        printArr(arr);
    }
    
    // Method to print the array
    public static void printArr(int[] arr) {
        for (int num : arr) {
            System.out.print(num + " ");  // Add space between numbers
        }
        System.out.println();
    }

    // Method to reverse the array
    public static void revArr(int[] arr) {
        int start = 0;
        int end = arr.length - 1;
        while (start < end) {
            int temp = arr[start];
            arr[start] = arr[end];
            arr[end] = temp;
            start++;
            end--;
        }
    }
}

Original array: 1 5 2 5 7 
Reversed array: 7 5 2 5 1

Key Features

Reversing Logic:
The revArr method uses two pointers: start and end.
The pointers begin at opposite ends of the array and move towards the center, swapping elements as they go.

Printing the Array:
The printArr method iterates over the array using an enhanced for loop and prints its elements with spaces in between.

Efficiency:
The reversal algorithm runs in O(n) time since each element is accessed only once.
The space complexity is O(1) because the reversal is performed in-place without extra storage.

Why This Method?
In-place operation: Avoids creating a new array, saving memory.
Two-pointer technique: Simple and effective for array reversal.