How does Xor work in swapping values?

Here is the original code:

public static String reverseString(String s){           if(s == null) return "";            char[] rev = s.toCharArray();    int i = 0, j = s.length() - 1;    while(i < j) {        rev[i] ^= rev[j];        rev[j] ^= rev[i];        rev[i++] ^= rev[j--];               }           return String.valueOf(rev); }

My question is how does Xor work in swapping character values here, and why is rev[i++]^=rev[j--] needed here?