Swap adjacent characters of string with some conditions

Question

import java.io.*;
import java.util.*;
public class Test 
{
    public static String solve(String str) {
    String result = "Invalid string";  // prepare result
    if (null != str && str.length() % 2 == 0) { // check the null and length of the input
        
        char[] arr = str.toCharArray();
        
        for (int i = 0; i < arr.length; i += 2) {
            if (Character.isDigit(arr[i]) || Character.isDigit(arr[i + 1])) {
                // if any digit found, return "Invalid string"
                return result;
            }
            // do the swap
            char t = arr[i];
            arr[i] = arr[i + 1];
            arr[i + 1] = t;
        }
        // make the result string
        result = new String(arr);
    }
    return result;
}
    public static void main(String[] args) throws Exception 
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int t = Integer.parseInt(br.readLine());
        for(int i = 0; i < t; i++) 
        {
            String str = br.readLine();
            try
            {
                System.out.println(solve(str));
            }
            catch(Exception e)
            {
                System.out.println(e.getMessage());
            }
        }
    }
}

Only perform the swapping if length of string is even and does not contain numeric value. if string contain numeric value then throw exception invalid input. if string length is odd then throw exception invalid length.

Test Cases : 


INPUT:

4 ( represent the number of test-cases)

afafas
ajanta
sdf
sasfd3sf


OUTPUT: 

fafasa
janaat
invalid string length 
invalid input

Therefore swapping will be perform keep in mind these scenarios

Answer 1

Your code needs a little correction which I have pointed out below.

public static String solve(String str) {
     String result = "invalid string length";  // prepare result if the length is not correct
     if (null != str && str.length() % 2 == 0) { // check the null and length //of the input

         char[] arr = str.toCharArray();

         for (int i = 0; i < arr.length; i += 2) {
             if (Character.isDigit(arr[i]) || Character.isDigit(arr[i + 1])) {
                 // if any digit found, return "Invalid string"
                 return "invalid input"; // return this as digit is found
             }

             // do the swap
             char t = arr[i];
             arr[i] = arr[i + 1];
             arr[i + 1] = t;
         }
         // make the result string
         result = new String(arr);
     }

     return result;
 }

Answer 2

I ran the above program the above test case falied are for last two cases only. The result statement alone want to be changed.by default it has given -- Invalid string

• If length is odd it should print -- invalid string length
• If the string contains digit it should print -- invalid input

public static String solve(String str) {
    String result;  // prepare result
    if (null != str && str.length() % 2 == 0) { // check the null and length of the input
        
        char[] arr = str.toCharArray();

        for (int i = 0; i < arr.length; i += 2) {
            if (Character.isDigit(arr[i]) || Character.isDigit(arr[i + 1])) {
                // if any digit found, return "Invalid string"
                result = "invalid input";
                return result;
            }
            // do the swap
            char t = arr[i];
            arr[i] = arr[i + 1];
            arr[i + 1] = t;
        }
        // make the result string
        result = new String(arr);
    }
    else {
        result ="invalid string length";
    }
    return result;
}