Java String replace char

//package com.demo2s;

public class Main {
    public static void main(String[] argv) throws Exception {
        String str = "test test demo2s.com";
        String oldchars = "t";
        char newchar = 'a';
        System.out.println(replaceChars(str, oldchars, newchar));
    }/*from w  w  w .  j  a  va2 s  . c om*/

    /**
     * Like String.replace() except that it accepts any number of old chars.
     * Replaces any occurrances of 'oldchars' in 'str' with 'newchar'.
     * Example: replaceChars("Hello, world!", "H,!", ' ') returns " ello  world "
     */
    public static String replaceChars(String str, String oldchars, char newchar) {
        int pos = indexOfChars(str, oldchars);
        if (pos == -1) {
            return str;
        }

        StringBuilder buf = new StringBuilder(str);
        do {
            buf.setCharAt(pos, newchar);
            pos = indexOfChars(str, oldchars, pos + 1);
        } while (pos != -1);

        return buf.toString();
    }

    /**
     * Like String.indexOf() except that it will look for any of the
     * characters in 'chars' (similar to C's strpbrk)
     */
    public static int indexOfChars(String str, String chars, int fromIndex) {
        final int len = str.length();

        for (int pos = fromIndex; pos < len; pos++) {
            if (chars.indexOf(str.charAt(pos)) >= 0) {
                return pos;
            }
        }

        return -1;
    }

    /**
     * Like String.indexOf() except that it will look for any of the
     * characters in 'chars' (similar to C's strpbrk)
     */
    public static int indexOfChars(String str, String chars) {
        return indexOfChars(str, chars, 0);
    }

}