I'm not getting output for my palindrome program in Java

Question

import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {

        Scanner sc=new Scanner(System.in);
        int i;
        String A=sc.next();
        String B= "";
        /* Enter your code here. Print output to STDOUT. */
        for(i=A.length()-1;i<=0;i--){
        B = B+A.charAt(i);
        }

        if(A.equals(B)){
            System.out.println("Yes");
        }
        else{
            System.out.println("No");
        }


    }
}

I'm not getting the required output for my code. I'm a beginner in Java.

What output do you get for what input? And how are [concurrency] and [parallel-processing] involved? — akuzminykh, May 22 '20 at 16:59
Please edit your question to explain what output you are getting and what output you are wanting. — halfer, May 23 '20 at 11:04

score 1 · Answer 1 · answered May 22 '20 at 17:33

The reason your program isn't giving you the desired output is because your for-loop is incorrect.

for(i.A.length()-1; i <= 0; i--) {/.../}

You are basically saying, whilst i is less than or equal to zero, execute the loop. i by default is greater than 0.

You can achieve a Palindrome check multiple ways. 2 Examples.

Example 1 using for-loop:

String A = "radar";
String B = "";

for(int i = A.length()-1; i >= 0; i -- ){
    B = B + A.charAt(i);
}

System.out.println(A.equals(B) ? "Yes" : "No");

Example 2 with StringBuilder.

String A = "radar";
StringBuilder B = new StringBuilder(A).reverse();

System.out.println(A.equals(B) ? "Yes" : "No");

score 0 · Answer 2 · answered May 22 '20 at 17:12

You are constantly getting an output of "No" because you're checking if i is less than or equal to zero on each loop, while you should be checking for greater than or equal to.

Change for (i = A.length() - 1; i <= 0; i--)

to

for (i = A.length() - 1; i >= 0; i--)

score 0 · Answer 3 · answered May 22 '20 at 17:14

The for loop runs as long as the condition holds, in your case i<=0. Unless the input has length 0 this condition never holds, thus the body of the for loop never gets executed and you immediately skip to if(A.equals(B))... which will always be false (except for the input ""). It should be i>=0.

I'm not getting output for my palindrome program in Java

3 Answers3