Java Reverse a String

NOTE: Do not forget to do $\frac{len}{2}$ 1. Use StringBuffer 2. sb.charAt() 3. sb.setCharAt()

    public static String reverseStr(String s){
        int len = s.length();
        StringBuffer sb = new StringBuffer(s);
        for(int i = 0; i < len/2; i++){
            int rInx = len - 1 - i;
            char c = sb.charAt(i);
            sb.setCharAt(i, sb.charAt(rInx));
            sb.setCharAt(rInx, c);
        }
        return sb.toString();
    }

    fl("Reverse String 0");        
    String s = "abc";
    String rs = reverseStr(s);
    System.out.println(rs); //  => cba