arrays - Remove duplicate characters in a string in Java -

i started read famous "cracking coding interview" book.

design algorithm , write code remove duplicate characters in string without using additional buffer. note: 1 or 2 additional variables fine. copy of array not.

i found similar topic here : remove duplicate characters in string

the solution given author :

  public static void removeduplicates(char[] str) {   if (str == null) return;   int len = str.length;   if (len < 2) return;    int tail = 1;    (int = 1; < len; ++i) {        int j;         (j = 0; j < tail; ++j) {        if (str[i] == str[j]) break;        }         if (j == tail) {        str[tail] = str[i];        ++tail;      }   }   str[tail] = 0;  } 

the problem here author used array argument function. question : how can write algorithms string argument? because felt it's easier use array here , it's "avoid difficulty" of exercice (in opinion, i'm newly java developer).

how can write such algorithm?

java strings immutable, can't string without copying array buffer.