BigDecimal

BigDecimal

普通类型计算

public class Test{
    public static void main(String[] args) {
        System.out.println(0.06+0.01);
        System.out.println(1.0-0.42);
        System.out.println(4.015*100);
        System.out.println(303.1/1000);
    }

}

输出

0.06999999999999999
0.5800000000000001
401.49999999999994
0.30310000000000004

BigDecimal类

public class BigDecimalUilt {
    /**
     * 提供精确加法计算的add方法
     * @param value1 被加数
     * @param value2 加数
     * @return 两个参数的和
     */
    public static double add(double value1,double value2){
        BigDecimal b1 = new BigDecimal(Double.valueOf(value1));
        BigDecimal b2 = new BigDecimal(Double.valueOf(value2));
        return b1.add(b2).doubleValue();
    }
    
    /**
     * 提供精确减法运算的sub方法
     * @param value1 被减数
     * @param value2 减数
     * @return 两个参数的差
     */
    public static double sub(double value1,double value2){
        BigDecimal b1 = new BigDecimal(Double.valueOf(value1));
        BigDecimal b2 = new BigDecimal(Double.valueOf(value2));
        return b1.subtract(b2).doubleValue();
    }
    
    /**
     * 提供精确乘法运算的mul方法
     * @param value1 被乘数
     * @param value2 乘数
     * @return 两个参数的积
     */
    public static double mul(double value1,double value2){
        BigDecimal b1 = new BigDecimal(Double.valueOf(value1));
        BigDecimal b2 = new BigDecimal(Double.valueOf(value2));
        return b1.multiply(b2).doubleValue();
    }
    
    /**
     * 提供精确的除法运算方法div
     * @param value1 被除数
     * @param value2 除数
     * @param scale 精确范围
     * @return 两个参数的商
     * @throws IllegalAccessException
     */
    public static double div(double value1,double value2,int scale) throws IllegalAccessException{
        //如果精确范围小于0，抛出异常信息
        if(scale<0){         
            throw new IllegalAccessException("精确度不能小于0");
        }
        BigDecimal b1 = new BigDecimal(Double.valueOf(value1));
        BigDecimal b2 = new BigDecimal(Double.valueOf(value2));
        return b1.divide(b2, scale).doubleValue();    
    }
}

add(BigDecimal augend)方法源码

public BigDecimal  add(BigDecimal augend) {
  long xs =this.intCompact; //整型数字表示的BigDecimal,例a的intCompact值为122
  long ys = augend.intCompact;//同上
  BigInteger fst = (this.intCompact !=INFLATED) ?null :this.intVal;//初始化BigInteger的值，intVal为BigDecimal的一个BigInteger类型的属性
  BigInteger snd =(augend.intCompact !=INFLATED) ?null : augend.intVal;
  int rscale =this.scale;//小数位数

  long sdiff = (long)rscale - augend.scale;//小数位数之差

  if (sdiff != 0) {//取小数位数多的为结果的小数位数
   if (sdiff < 0) {
     int raise =checkScale(-sdiff);
     rscale =augend.scale;
     if (xs ==INFLATED ||
       (xs = longMultiplyPowerTen(xs,raise)) ==INFLATED)
       fst =bigMultiplyPowerTen(raise);
    }else {
      int raise =augend.checkScale(sdiff);
      if (ys ==INFLATED ||(ys =longMultiplyPowerTen(ys,raise)) ==INFLATED)
        snd = augend.bigMultiplyPowerTen(raise);
    }
  }

  if (xs !=INFLATED && ys !=INFLATED) {
   long sum = xs + ys;
   if ( (((sum ^ xs) &(sum ^ ys))) >= 0L)//判断有无溢出
     return BigDecimal.valueOf(sum,rscale);//返回使用BigDecimal的静态工厂方法得到的BigDecimal实例
  }
  if (fst ==null)
    fst =BigInteger.valueOf(xs);//BigInteger的静态工厂方法

  if (snd ==null)
    snd =BigInteger.valueOf(ys);

  BigInteger sum =fst.add(snd);
  return (fst.signum == snd.signum) ?new BigDecimal(sum,INFLATED, rscale, 0) :
   new BigDecimal(sum,compactValFor(sum),rscale, 0);//返回通过其他构造方法得到的BigDecimal对象
}