Palindrome using args; help me find the error?

Question

I am building a class that checks if the input contains palindromes and returns only the palindrome terms if they exist. I have been able to develop the following, and it compiles and runs without errors, but I am not getting any return from it.

Can anyone spot where my error lies?

public class Palindrome {

public static boolean isPalindrome(String word) {

    String back = word.charAt(word.length() - 1) + "";
    for (int i = word.length() - 2; i >= 0; i--) {
        back = back + word.charAt(i);
    }
    if (word == back) {
        return true;
    }
    return false;
}


public static void main(String[] args) {
    for (int i = 0; i < args.length; i++) {
        if (isPalindrome(args[i]) == true) {
            System.out.println(args[i]);
        }
    }

}

}

I believe the issue lies in the main method, specifically within the if statement, but I'm not exactly sure why it's not working.

public static void main(String[] args) {
    for (int i = 0; i < args.length; i++) {
        if (isPalindrome(args[i]) == true) {
            System.out.println(args[i]);
        }
    }

}

Thank you in advance for any help offered. I appreciate your time!

You can check for palindromes much more efficiently by doing it in place. But that's another question. The big O of this implementation is actually n^2. — Daniel Williams, Sep 04 '13 at 23:15

SWPhantom · Answer 1 · 2013-09-04T23:07:27.360

1

Seconded on the .equals() error.

Also, you can easily check for palindromes by using the built-in String reversal procedure:

String a = "sampleelpmas";
String b = new StringBuffer(a).reverse().toString();

a.equals(b); //TRUE

edited Sep 04 '13 at 23:07

answered Sep 04 '13 at 23:01

SWPhantom

674
5
18

1

The output is false. It is not a palindrome. – Pawel Sep 04 '13 at 23:05
hahaha. You're right. Editing for anti-foolishness. – SWPhantom Sep 04 '13 at 23:07
Now the output is correct ;). – Pawel Sep 04 '13 at 23:09
This is why Pair Programming is the best! ;D – SWPhantom Sep 04 '13 at 23:15
1

Pair programming is pretty good. But if we compare personal programming with pair, we compare time spent, number of errors, then conclusion would be in my opinion: programming by one person is better for employer:(, even if number of errors is less. Only one person gets payment. – Pawel Sep 04 '13 at 23:21

score 1 · Answer 2 · answered Sep 04 '13 at 23:01

For the first part, you could reverse it using back = new StringBuilder(word).reverse().toString(), which is cleaner code and also more optimized (also faster but doesn't matter here).

But your problem is at comparing strings, == check if both objects are equal and this is never true for 2 strings, even if they're the same like you were expecting. Use word.equals(back), which check if text contents of string match.

Pawel · Answer 3 · 2013-09-04T23:03:28.683

0

Common error. Comparison of string is wrong. Do not use == operator. Use equals() method.

Change word == back to word.equals(back).

Rest should be right.

edited Sep 04 '13 at 23:03

answered Sep 04 '13 at 22:58

Pawel

1,457
1
11
22

score 0 · Answer 4 · answered Sep 04 '13 at 22:59

0

You shouldn't use == to evaluate String equality, use equals() instead.

if (word.equals(back))

answered Sep 04 '13 at 22:59

MasterOfBinary

245
1
12

Palindrome using args; help me find the error?

4 Answers4