Java program to swap characters in a string

Question

I am writing a Java program to encrypt a four digit number. Some procedures require to swap 1st digit with 3rd and 2nd with 4th... Here's what I have written, but it's not working. for example, if my input is 9876 then after these four swaps it gives output 9898. which means that first and third Swaps are not working. But if I comment the second and fourth swaps then 1st and 3rd swap works.

 char ch;
 ch=str.charAt(0);
        str=str.replace(str.charAt(0),str.charAt(2));
        str=str.replace(str.charAt(2),ch);


        ch=str.charAt(1);
        str=str.replace(str.charAt(1),str.charAt(3));
        str=str.replace(str.charAt(3),ch);

Juvanis · Accepted Answer · 2014-05-10 15:11:49Z

2

Retrieve the internal character array of your String instance by a call to toCharArray() and then swap the particular elements of that char array with a robust helper swap() method. Then convert your modified char array back to a String.

answered May 10, 2014 at 15:11

Juvanis

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Kostas Kryptos · Accepted Answer · 2014-05-10 15:18:57Z

1

You can also use substring, eg:

str = str.substring(2,3) + str.substring(3,4) + str.substring(0,1) + str.substring(1,2);

Change last Two digits with first two is also equivalent (it fits your case and it's faster):

str = str.substring(2,4) + str.substring(0,2);

answered May 10, 2014 at 15:18

Kostas Kryptos

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