java.lang.ArithmeticException: Non-terminating decimal expansion； no exactrepresentabledecimalresult

问题

简单记录下在使用BigDecimal时碰到的异常，改异常是在使用divide这个方法时，由于除出来的结果是无限小数导致的。

解决方法

解决很简单，为divide方法设置精确的小数点，如：a.divide(b,1),保留1位小数。

divide源码

    /**
     * Returns a {@code BigDecimal} whose value is {@code (this /
     * divisor)}, and whose scale is as specified.  If rounding must
     * be performed to generate a result with the specified scale, the
     * specified rounding mode is applied.
     *
     * <p>The new {@link #divide(BigDecimal, int, RoundingMode)} method
     * should be used in preference to this legacy method.
     *
     * @param  divisor value by which this {@code BigDecimal} is to be divided.
     * @param  scale scale of the {@code BigDecimal} quotient to be returned.
     * @param  roundingMode rounding mode to apply.
     * @return {@code this / divisor}
     * @throws ArithmeticException if {@code divisor} is zero,
     *         {@code roundingMode==ROUND_UNNECESSARY} and
     *         the specified scale is insufficient to represent the result
     *         of the division exactly.
     * @throws IllegalArgumentException if {@code roundingMode} does not
     *         represent a valid rounding mode.
     * @see    #ROUND_UP
     * @see    #ROUND_DOWN
     * @see    #ROUND_CEILING
     * @see    #ROUND_FLOOR
     * @see    #ROUND_HALF_UP
     * @see    #ROUND_HALF_DOWN
     * @see    #ROUND_HALF_EVEN
     * @see    #ROUND_UNNECESSARY
     */
    public BigDecimal divide(BigDecimal divisor, int scale, int roundingMode) {
        if (roundingMode < ROUND_UP || roundingMode > ROUND_UNNECESSARY)
            throw new IllegalArgumentException("Invalid rounding mode");
        if (this.intCompact != INFLATED) {
            if ((divisor.intCompact != INFLATED)) {
                return divide(this.intCompact, this.scale, divisor.intCompact, divisor.scale, scale, roundingMode);
            } else {
                return divide(this.intCompact, this.scale, divisor.intVal, divisor.scale, scale, roundingMode);
            }
        } else {
            if ((divisor.intCompact != INFLATED)) {
                return divide(this.intVal, this.scale, divisor.intCompact, divisor.scale, scale, roundingMode);
            } else {
                return divide(this.intVal, this.scale, divisor.intVal, divisor.scale, scale, roundingMode);
            }
        }
    }

这是以前的divide方法，现在有个新的divide方法，我们先看看这个遗留方法

• 返回一个 BigDecimal 类型的值，其值为 两者相除，其scale（scale指你要保留的小数点位数，或者叫精度）为指定的。
• 如果必须执行舍入以生成具有指定scale（精度）的结果，则应用指定的舍入模式。 应该优先使用新的divide方法 #divide(BigDecimal, int, RoundingMode) 而不是这种遗留方法。
• 参数 divisor 被除以的 值。
• 参数 scale 要返回商的保留小数的位数。
• 参数 roundingMode 要使用的舍入模式。
• 返回值 return {@code this / divisor}
• 异常 throws ArithmeticException 如果 {除数 divisor} 为零，{@code roundingMode==ROUND_UNNECESSARY} 并且指定的比例不足以准确表示除法的结果,会抛出算数异常。
• 异常 throws IllegalArgumentException 如果 roundingMode 参数不是他规定的那几个舍入模式，就会抛非法参数异常（让你不听大哥的！）。
  #ROUND_UP
  #ROUND_DOWN
  #ROUND_CEILING
  #ROUND_FLOOR
  #ROUND_HALF_UP 常用的四舍五入(保留位后一位是5进位)
  #ROUND_HALF_DOWN 四舍五入(保留位后一位是5舍弃
  #ROUND_HALF_EVEN
  #ROUND_UNNECESSARY

---

这是新的divide方法

/**
 * Returns a {@code BigDecimal} whose value is {@code (this /
 * divisor)}, and whose scale is as specified.  If rounding must
 * be performed to generate a result with the specified scale, the
 * specified rounding mode is applied.
 *
 * @param  divisor value by which this {@code BigDecimal} is to be divided.
 * @param  scale scale of the {@code BigDecimal} quotient to be returned.
 * @param  roundingMode rounding mode to apply.
 * @return {@code this / divisor}
 * @throws ArithmeticException if {@code divisor} is zero,
 *         {@code roundingMode==RoundingMode.UNNECESSARY} and
 *         the specified scale is insufficient to represent the result
 *         of the division exactly.
 * @since 1.5
 */
public BigDecimal divide(BigDecimal divisor, int scale, RoundingMode roundingMode) {
    return divide(divisor, scale, roundingMode.oldMode);
}

总结

源码是越点越恐怖，有兴趣的朋友可以自己去点一点，（w点点,q点点,e点点嘟嘟嘟嘟嘟嘟嘟嘟嘟嘟嘟）

总结一下（说人话），divide方法，A.divide(B, 2 ,ROUND_HALF_UP)
A / B ,2 指的是保留两位小数，四舍五入，例如结果是2.366，执行后就是2.37；2.4333，执行后就是2.43

贴一个看到的有关bigdecimal的总结文章，写的蛮好的值得收藏！！！