public String nextString() {
    String returnedString = null;
    if(length == 0){
        returnedString = "";
    }
    else{
        for (int idx = 0; idx < buf.length; ++idx){ 
            buf[idx] = symbols[random.nextInt(symbols.length)];
            returnedString = new String(buf);
        }
    }
    
    return returnedString;  
  }