Write a Java Program to reverse a given string without using any built-in String reversal methods such as reverse().

Question

Accepted Answer

Approach:
The solution traverses the string from the last character to the first character and appends each character to a result string. This manually constructs the reversed string without relying on any built-in reversal functionality.

This approach demonstrates a clear understanding of string manipulation and iteration, which is commonly evaluated in Java interviews.

Java Solution:
```
public class ReverseString {

public static String reverse(String input) {
        String reversedString = "";

for (int index = input.length() - 1; index >= 0; index--) {
            reversedString += input.charAt(index);
        }

return reversedString;
    }

public static void main(String[] args) {
        String input = "Java";

String reversedString = reverse(input);

System.out.println("Original String: " + input);
        System.out.println("Reversed String: " + reversedString);
    }
}
```
Output:
Original String: Java
Reversed String: avaJ

Time Complexity:
O(n), where n is the length of the string since each character is processed exactly once.

Space Complexity:
O(n), as a new string is created to store the reversed result.

Key Interview Points:
• This solution avoids using built-in reversal methods such as StringBuilder.reverse().
• Using String concatenation inside a loop creates multiple intermediate String objects due to String immutability.
• A more efficient production approach is to use a character array or StringBuilder for O(n) time with reduced object creation.