@Override public String toString(){
  StringBuilder sb=new StringBuilder();
  sb.append(String.format("%d ",firstZero));
  for (int i=0; i < Math.max(INITIAL_LENGTH,bits.length()); i++) {
    sb.append(bits.get(i) ? "x" : ".");
  }
  return sb.toString();
}

@ Override public String toString ( ) { StringBuilder sb = new StringBuilder ( ) ; sb . append ( String . format ( "%d " , firstZero ) ) ; for ( int i = 0 ; i < Math . max ( INITIAL_LENGTH , bits . length ( ) ) ; i ++ ) { sb . append ( bits . get ( i ) ? "x" : "." ) ; } return sb . toString ( ) ; }
pretty - prints the coverage vector , making a guess about the length
