reversing text in Java

Question

I'm trying to reverse a string in Java but I get an error I don't understand when I run it:

"Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 3
at java.lang.String.charAt(String.java:658)
at ReversingText.reverse(ReversingText.java:13)
at ReversingText.main(ReversingText.java:27)"

This is my code:

import java.util.Scanner;

public class ReversingText {

    public static String reverse(String text) {
        int i = (text.length() - 1);

        String letter = "";

        while (i >= 0) {

            char character = letter.charAt(i);

            letter += character;
            i--;

        }

        return letter;
    }

    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);
        System.out.print("Type in your text: ");
        String text = reader.nextLine();
        System.out.println("In reverse order: " + reverse(text));
    }

}

Not sure where the problem is, as I think index starts at 0 so I decrease length of the string by 1 to find index?

Thanks for any help

Hi Elly. your program is now working. please upvote or correct the answer. — Pradeep Singh, Jun 09 '17 at 21:04

score 2 · Accepted Answer · answered Jun 09 '17 at 20:24

The problem is you are trying to get the character of variable letter (which starts as an empty string, therefore with no length and thus no valid index) instead of text:

char character = letter.charAt(i);

Try this:

char character = text.charAt(i);

Pradeep Singh · Answer 2 · 2017-06-09T20:30:42.223

1

There were other mistakes. This is the correct programme.

public class ReversingText {
    public static String reverse(String text) {
            int i = (text.length() - 1);
            String letter = text;
            String reverseletter = "";
            while (i >= 0) {
                char character = letter.charAt(i);
                reverseletter += character;
                i--;
            }
            return reverseletter;
        }

        public static void main(String[] args) {
            Scanner reader = new Scanner(System.in);
            System.out.print("Type in your text: ");
            String text = reader.nextLine();
            System.out.println("In reverse order: " + reverse(text));
        }
}

edited Jun 09 '17 at 20:30

answered Jun 09 '17 at 20:27

Pradeep Singh

1,094
1
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24

What mistakes? Can you clarify? – flogy Jun 09 '17 at 20:29
1

Yes wil explain. Please correct my answer if it solves the problem. – Pradeep Singh Jun 09 '17 at 20:30
1

These 2 lines were the cause of problem. String letter = text; I have made a new string variable to pick up reverse value. String reverseletter = ""; You were taking old string letter value only. so old original and reverse string were appending to each other. by creating new reverseletter variable, it solves the problem. thanks:) – Pradeep Singh Jun 09 '17 at 20:33
1

@flogy you can make my answer correct. If it solves the programme. – Pradeep Singh Jun 09 '17 at 20:36
I'm not the OP, so I can't. – flogy Jun 09 '17 at 20:38
1

OP means what? output? – Pradeep Singh Jun 09 '17 at 20:39
"Original poster". I did not ask this question, but @Elly. – flogy Jun 09 '17 at 20:41
1

Oh sorry I am in too hurry. ;) @Elly you got the solution?? – Pradeep Singh Jun 09 '17 at 20:43
1

Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/146303/discussion-between-pradeep-singh-and-flogy). – Pradeep Singh Jun 09 '17 at 21:07

score 1 · Answer 3 · answered Jun 09 '17 at 20:34

The problem is you are finding the char at index i in the empty String letter. When the while loop runs for the first time, i = 3 and there is no char at index 3 in letter.

Instead, call charAt(i) on text:

public static String reverse(String text) {
    int i = text.length() - 1;

    String letter = "";

    while (i >= 0) {
        char character = text.charAt(i);
        letter += character;
        i--;
    }

    return letter;
}

Alternatively, for a much simpler way of reversing text, use:

public static String reverse(String text) {
    return new StringBuilder(text).reverse().toString();
}

See also: Reverse a string in Java

Upvote for also mentioning easy solution and link to related documentation. — flogy, Jun 09 '17 at 20:35

score 0 · Answer 4 · answered Jun 09 '17 at 20:31

Another tip:

In the end, remember to close the reader.

public static void main(String[] args) {
    Scanner reader = new Scanner(System.in);
    System.out.print("Type in your text: ");
    String text = reader.nextLine();
    System.out.println("In reverse order: " + reverse(text));
    reader.close(); // add this line
}

score 0 · Answer 5 · edited Jun 09 '17 at 21:05

The problem were in this line: char character = letter.charAt(i); You've worked with letter instead of text)

Here is the working code:

import java.util.Scanner;

public class ReversingText {

    public static String reverse(String text) {
        int i = text.length()-1;
        System.out.println("length: " + i);

        String letter = "";

        while (i >= 0) {

            char character = text.charAt(i);

            letter += character;
            i--;

        }

        return letter;
    }

    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);
        System.out.print("Type in your text: ");
        String text = reader.nextLine();
        System.out.println("In reverse order: " + reverse(text));
    }

}

run the porgram. if you will want to reverse of pradeep you will get this result. pradeeppeedarp. So need to change little more as in my code. ;) — Pradeep Singh, Jun 09 '17 at 21:06

Oghli · Answer 6 · 2017-06-09T21:10:23.377

The problem at this line:

char character = letter.charAt(i);

You should manipulate with text variable instead of letter :

char character = text.charAt(i);

Also you can achieve that in another approach using Stack data structure:

public static String reverse(String text) {
    Stack<Character> st = new Stack<Character>();
    String rtext = "";
    for(int i = 0; i < text.length(); i++){
        st.push(text.charAt(i));
    }
    while(!st.empty()){
        rtext = rtext + st.pop();
    }
   return rtext;
}

reversing text in Java

6 Answers6