public HoltWintersModelBuilder alpha(double alpha){
  this.alpha=alpha;
  return this;
}

public HoltWintersModelBuilder alpha ( double alpha ) { this . alpha = alpha ; return this ; }
alpha controls the smoothing of the data . alpha = 1 retains no memory of past values ( e . g . a random walk ) , while alpha = 0 retains infinite memory of past values ( e . g . the series mean ) . useful values are somewhere in between . defaults to 0 . 5 .
