Reverse an Array in Java Without Using Built-in Methods

Reversing an array is a classic problem often asked in Java interviews. In this tutorial, we'll reverse an array manually without using Collections.reverse() or Arrays utility classes.

🧮 Logic

We use two pointers: one starting from the beginning, and one from the end. Swap their values while moving toward the center.

✅ Java Program

public class ReverseArray {
    public static void main(String[] args) {
        int[] arr = {10, 20, 30, 40, 50};

        System.out.println("Original Array:");
        printArray(arr);

        reverseArray(arr);

        System.out.println("Reversed Array:");
        printArray(arr);
    }

    static void reverseArray(int[] arr) {
        int start = 0, end = arr.length - 1;
        while (start < end) {
            int temp = arr[start];
            arr[start] = arr[end];
            arr[end] = temp;
            start++;
            end--;
        }
    }

    static void printArray(int[] arr) {
        for (int num : arr) {
            System.out.print(num + " ");
        }
        System.out.println();
    }
}

🧠 Interview Tip

This question is often followed by variations like "reverse only even elements" or "reverse using recursion." Make sure to explain your swap logic clearly.

✅ Output

Original Array:
10 20 30 40 50 
Reversed Array:
50 40 30 20 10 

📌 Conclusion

We learned how to reverse an array in Java using simple loop logic and without relying on any built-in methods. This program builds your core understanding of arrays and data manipulation.