CODEWITHSUNDEEP
java
Elly
Elly

Reputation: 39

reversing text in Java

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

Upvotes: 0

Views: 436

Answers (6)

Oghli
Oghli

Reputation: 2340

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;
}

Upvotes: 0

Elvira Parpalac
Elvira Parpalac

Reputation: 31

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));
    }

}

Upvotes: 0

Aditya Gupta
Aditya Gupta

Reputation: 55

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

Upvotes: 1

Alexandre Mucci
Alexandre Mucci

Reputation: 119

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
}

Upvotes: 0

Pradeep Singh
Pradeep Singh

Reputation: 1144

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));
        }
}

Upvotes: 1

flogy
flogy

Reputation: 937

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);

Upvotes: 2

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