How to swap String characters in Java?

Question

How can I swap two characters in a String? For example, \"abcde\" will become \"bacde\".

Answer 1

'In' a string, you cant. Strings are immutable. You can easily create a second string with:

 String second = first.replaceFirst("(.)(.)", "$2$1");

Answer 2

Since String objects are immutable, going to a char[] via toCharArray, swapping the characters, then making a new String from char[] via the String(char[]) constructor would work.

The following example swaps the first and second characters:

String originalString = "abcde";

char[] c = originalString.toCharArray();

// Replace with a "swap" function, if desired:
char temp = c[0];
c[0] = c[1];
c[1] = temp;

String swappedString = new String(c);

System.out.println(originalString);
System.out.println(swappedString);

Result:

abcde
bacde

Answer 3

StringBuilder sb = new StringBuilder("abcde");
    sb.setCharAt(0, 'b');
    sb.setCharAt(1, 'a');
    String newString = sb.toString();

Answer 4

Here's a solution with a StringBuilder. It supports padding resulting strings with uneven string length with a padding character. As you've guessed this method is made for hexadecimal-nibble-swapping.

/**
 * Swaps every character at position i with the character at position i + 1 in the given
 * string.
 */
public static String swapCharacters(final String value, final boolean padding)
{
   if ( value == null )
   {
      return null;
   }

   final StringBuilder stringBuilder = new StringBuilder();
   int posA = 0;
   int posB = 1;
   final char padChar = 'F';

   // swap characters
   while ( posA < value.length() && posB < value.length() )
   {
      stringBuilder.append( value.charAt( posB ) ).append( value.charAt( posA ) );
      posA += 2;
      posB += 2;
   }

   // if resulting string is still smaller than original string we missed the last
   // character
   if ( stringBuilder.length() < value.length() )
   {
      stringBuilder.append( value.charAt( posA ) );
   }

   // add the padding character for uneven strings
   if ( padding && value.length() % 2 != 0 )
   {
      stringBuilder.append( padChar );
   }

   return stringBuilder.toString();
}

Answer 5

//this is a very basic way of how to order a string alpha-wise, this does not use anything fancy and is great for school use

package string_sorter;

public class String_Sorter {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {

    String word = "jihgfedcba";
    for (int endOfString = word.length(); endOfString > 0; endOfString--) {

        int largestWord = word.charAt(0);
        int location = 0;
        for (int index = 0; index < endOfString; index++) {

            if (word.charAt(index) > largestWord) {

                largestWord = word.charAt(index);
                location = index;
            }
        }

        if (location < endOfString - 1) {

            String newString = word.substring(0, location) + word.charAt(endOfString - 1) + word.substring(location + 1, endOfString - 1) + word.charAt(location);
            word = newString;
        }
        System.out.println(word);
    }

    System.out.println(word);
}

}

Answer 6

The following line of code will swap the first two characters in str:

return str.charAt(1) + str.charAt(0) + str.substring(2);