How to swap String characters in Java?

Question

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

Answer 1

String.replaceAll() or replaceFirst()

String s = "abcde".replaceAll("ab", "ba")

Link to the JavaDocs String API

Answer 2

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

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

Answer 3

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 = s.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 4

String.toCharArray() will give you an array of characters representing this string.

You can change this without changing the original string (swap any characters you require), and then create a new string using String(char[]).

Note that strings are immutable, so you have to create a new string object.

Answer 5

This has been answered a few times but here's one more just for fun :-)

public class Tmp {
    public static void main(String[] args) {
        System.out.println(swapChars("abcde", 0, 1));
    }
    private static String swapChars(String str, int lIdx, int rIdx) {
        StringBuilder sb = new StringBuilder(str);
        char l = sb.charAt(lIdx), r = sb.charAt(rIdx);
        sb.setCharAt(lIdx, r);
        sb.setCharAt(rIdx, l);
        return sb.toString();
    }
}