public class TestDouble {
  //兩個Double數(shù)相減
  public static Double sub(Double d1, Double d2) {
    if (d1 == null || d2 == null) {
      return null;
    }
    BigDecimal b1 = new BigDecimal(d1.toString());
    BigDecimal b2 = new BigDecimal(d2.toString());
    return b1.subtract(b2).doubleValue();
  }
 
  //兩個Double數(shù)相加
  public static Double add(Double d1, Double d2) {
    if (d1 == null || d2 == null) {
      return null;
    }
    BigDecimal b1 = new BigDecimal(d1.toString());
    BigDecimal b2 = new BigDecimal(d2.toString());
    return b1.add(b2).doubleValue();
  }
 
  //兩個Double數(shù)相除，并保留scale位小數(shù)
  public static Double div(Double d1, Double d2, int scale) {
    if (d1 == null || d2 == null || scale < 0) {
      return null;
    }
    BigDecimal b1 = new BigDecimal(d1.toString());
    BigDecimal b2 = new BigDecimal(d2.toString());
    return b1.divide(b2, scale, BigDecimal.ROUND_HALF_UP).doubleValue();
  }
 
  // 兩個Double數(shù)相乘
  public static Double mul(Double d1, Double d2) {
    if (d1 == null || d2 == null) {
      return null;
    }
    BigDecimal b1 = new BigDecimal(d1.toString());
    BigDecimal b2 = new BigDecimal(d2.toString());
    return b1.multiply(b2).doubleValue();
  }
 
  /**
   * 遇到.5的情況時往上近似
   *
   * @param d
   * @param scale
   * @return
   */
  public static Double setDoubleScale(Double d, int scale) {
    if (d == null || scale < 0) {
      return null;
    }
    BigDecimal b = new BigDecimal(d);
    return b.setScale(scale, BigDecimal.ROUND_HALF_UP).doubleValue();
  }
 
  public static void main(String[] args) {
    Double d1 = 2099d;
    Double d2 = 1999.999;
    System.out.println(d1 - d2);
    System.out.println(sub(d1, d2));
    System.out.println("------------------------------------");
    System.out.println(d1 * d2);
    System.out.println(mul(d1, d2));
    System.out.println("------------------------------------");
    System.out.println(d1/d2);
    System.out.println(div(d1,d2,4));
 
  }
}