In this sentence reversal program, why has char been used and not String? [closed]

Question

I was doing a few beginner coding challenges and one of the challenge was making a program that reverses a given String. It worked on words, but as soon as I put in words with spaces between them the program only reversed the first word entered.

I googled "reverse words with spaces in it java" and found this:

// Java program to reverse a string
// preserving spaces.
public class ReverseStringPreserveSpace {
    // Function to reverse the string
    // and preserve the space position
    static void reverses(String str)
    {
 
        char[] inputArray = str.toCharArray();
        char[] result = new char[inputArray.length];
 
        // Mark spaces in result
        for (int i = 0; i < inputArray.length; i++) {
            if (inputArray[i] == ' ') {
                result[i] = ' ';
            }
        }
 
        // Traverse input string from beginning
        // and put characters in result from end
        int j = result.length - 1;
        for (int i = 0; i < inputArray.length; i++) {
 
            // Ignore spaces in input string
            if (inputArray[i] != ' ') {
 
                // ignore spaces in result.
                if (result[j] == ' ') {
                    j--;
                }
                result[j] = inputArray[i];
                j--;
            }
        }
        System.out.println(String.valueOf(result));
    }
 
    // driver function
    public static void main(String[] args)
    {
        reverses("internship at geeks for geeks");
    }
}

1. Why were char arrays used instead of String directly?

2. Can I modify my own code to make it reverse a sentence without following the above code? My code:

import java.util.Scanner;

class ReverseString
{
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.println("Enter the word to be reversed:");
        String input = s.next();

        String reversed = "";
        for (int i = 0; i < input.length(); i++)
        {
            char ch = input.charAt(i);
            reversed = ch + reversed;
        }
        System.out.println(reversed);
    }
}