Java中double四捨五入的函數

public String format(int size,double number){
StringBuffer formatString = new StringBuffer("0");
  if(size>0){
   formatString.append(".");
  }
  for (int i = 0; i < size; i++) {
   formatString.append("#");
  }
  DecimalFormat df = new DecimalFormat(formatString.toString());
 return df.format(number);
}