You're storing your reversed number as an int. The reverse of 1200 is 0021, but that's just 21 as an int. You can fix it by converting each digit to a string separately.

You only need to iterate across the string halfway, swapping the characters as the indices go towards the middle. This works for even or odd length strings.

Scanner sc = new Scanner(System.in);
System.out.print("Enter a number:- ");
char[] chars = sc.next().toCharArray();
int len = chars.length;
for (int i = 0; i < len/2; i++) {
     char c1 = chars[i];
     char c2 = chars[len-i-1];
     chars[i] = c2;
     chars[len-i-1] = c1;
}
String s = new String(chars);
System.out.println(s);

Or just use the reverse() method included in the StringBuilder class.

import java.util.Scanner;public class ReverseString{	public static void main(String[] args)	{		System.out.println("Enter string to reverse:");				Scanner read = new Scanner(System.in);		String str = read.nextLine();				StringBuilder sb = new StringBuilder(str);				System.out.println("Reversed string is:");		System.out.println(sb.reverse().toString());	}}

First possibility use String

You can use directly the String as your data structure. Adding at the beginning instead of at the end when you read a new number.

Basically with a code like:

String str = "";
while (yourcondition) {
    str = scanner.nextInt() + " " + str;
}
return str;

Second possibility use StringBuffer or StringBuilder

StringBuilder str = new StringBuilder();
while (yourcondition) {
    str.insert(0, " ").insert(0, scanner.nextInt());
}
return str.toString();

Third possibility use recursion:

public String read(String str, Scanner scanner) {
    if (testExitCondition) {
        return str;
    }
    return scanner.nextInt() + " " + str;
}

// Called with System.out.println(read("", scanner));

Note

The first solution use String creating many instances of String, but having only one reference to it.

The second solution use existing classes that internally uses arrays to operate on strings.

The third leave to the JVM the reference to the created String, so no explicit reference to the string is present in the code. This is the only that don't have explicit variable declarations (only in the signature of method, not outside).