Invert chars inside string array

Question

I'm taking care of some other methods and I don't know what to do with this one. I want to change the order of the string inside the array (not the order of the string*s*), but this isn't accepted. Any ideas?

public void invert() {

        for(int i = 0; i < array.length; i++){
            for(int j = 0, k = array[i].length() - 1; j < k; j++, k--){
                char a = array[i].charAt(j);
                array[i].charAt(j) = array[k].charAt(k); //ERROR HERE
                array[i].charAt(k) = a;                  //AND HERE
            }
        }
    }

EDIT: I'll leave here what I mean. I have an array = {"Hello", "Goodbye"} I want to change it to {"olleH", "eybdooG"}

Use new StringBuilder.reverse().

Masudul
– Masudul

2013-12-11 17:57:56 +00:00
Commented Dec 11, 2013 at 17:57 — Masudul
– Masudul, Commented Dec 11, 2013 at 17:57

Martin Majer · Accepted Answer · 2013-12-11 17:59:58Z

4

Java string are immutable. You can't change them.

(But you can convert the string to a StringBuilder - http://docs.oracle.com/javase/tutorial/java/data/buffers.html - which is essentialy a mutable string, change the characters, and then convert the StrignBuilder back to String.)

Try this code (I haven't tested it, but I hope it works):

    for(int i = 0; i < array.length; i++) {
        StringBuilder b = new StringBuilder(array[i]);
        for(int j = 0, k = b.length() - 1; j < k; j++, k--){
            char a = b.charAt(j);
            b.setCharAt(j, array[k].charAt(k));
            b.setCharAt(k, a);                  
        }
        array[i] = b.toString();
    }

edited Dec 11, 2013 at 17:59

answered Dec 11, 2013 at 17:54

Martin Majer

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2 Comments

WiredDrummer Over a year ago

Thanks, it worked! Just one little thing, it was array[i].charAt(k). Was getting "java.lang.ArrayIndexOutOfBoundsException: 12" and couldn't figure out where hehe. Thanks!!

Martin Majer Over a year ago

Well, then you can use just this: b.setCharAt(j, b.charAt(k));.

Sage · Accepted Answer · 2013-12-11 18:26:38Z

2

array[i].charAt(j) = array[k].charAt(k); //ERROR HERE

array[i].charAt(a) returns a value not a variable. You are trying to assign a value to a value which doesn't make any sense.
java String is immutable. You can't change it.
Use StringBuilder which has setCharAt(int index, char ch); function which is what you are probably wanting.

edited Dec 11, 2013 at 18:26

answered Dec 11, 2013 at 17:57

Sage

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Comments

Masudul · Accepted Answer · 2013-12-11 17:59:34Z

0

The most simple way is, to reverse letter with StringBuilder.reverse() method. Try,

 for(String str : array){
   System.out.println(new StringBuilder(str).reverse());
 }

answered Dec 11, 2013 at 17:59

Masudul

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Comments

Flying Dumpling · Accepted Answer · 2013-12-11 17:59:51Z

0

Just use this on every String in your array:

String reversed = new StringBuilder(stringFromArray).reverse().toString();

answered Dec 11, 2013 at 17:59

Flying Dumpling

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Comments

Peter Lawrey · Accepted Answer · 2013-12-17 10:56:31Z

0

try doing new StringBuilder(array[i]).reverse().toString();

edited Dec 17, 2013 at 10:56

Peter Lawrey

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answered Dec 11, 2013 at 17:59

dev2d

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Comments

abysmaldan · Accepted Answer · 2013-12-11 17:58:26Z

-1

you would have to create a substring.

array[i]= array[i].substring(0,j) + array[k].charAt(k) + array[i].substring(j+1);

This would do the required edit i beleive

answered Dec 11, 2013 at 17:58

abysmaldan

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