How do I reverse a number in Java using String?-CodePudding

I have used the below logic, but getting an exception "java.lang.StringIndexOutOfBoundsException". Help will be appreciated. Thank you!!

import java.util.Scanner;
public class Demo{

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number:- ");
        String number = sc.next();                      

        for (int i = number.length(); i >= 0; i--) {    
            System.out.println(number.charAt(i));
        }

    }

}

CodePudding user response：

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.

CodePudding user response：

import java.util.Scanner;
public class Demo{

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number:- ");
        String number = sc.next();                      

        for (int i = number.length() -1 ; i >= 0; i--) {    // correct answer: number.lenght() -1 as array start with 0.
            System.out.print(number.charAt(i)); //using print instead of println so that it display in same line
        }

    }

}