BIgDecimal()和BigInteger()运算add(),sub(),div(),muti()加减乘除其实都是有返回值的

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
    //初始化BigInteger的值，intVal为BigDecimal的一个BigInteger类型的属性
    BigInteger fst = (this.intCompact !=INFLATED) ?null :this.intVal;
    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
         //返回使用BigDecimal的静态工厂方法得到的BigDecimal实例
         return BigDecimal.valueOf(sum,rscale);
    }
    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);
    //返回通过其他构造方法得到的BigDecimal对象
    return (fst.signum == snd.signum) ?new BigDecimal(sum,INFLATED, rscale, 0) :
      new BigDecimal(sum,compactValFor(sum),rscale, 0);
}