bigdecimal.round_down

"bigdecimal.round_down" 指的是使用 BigDecimal 类中的 round() 方法, 并将舍入模式设置为 RoundingMode.DOWN。这将导致舍去任何需要舍入的小数部分, 保留整数部分.

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BigDecimal.ROUND_DOWN

BigDecimal.ROUND_DOWN is a rounding mode used in the BigDecimal class in Java. It specifies that a number should be rounded down to the nearest digit based on the scale (number of decimal places) of the BigDecimal object.

For example, if a BigDecimal object has a value of 3.456 and a scale of 2, rounding down with the ROUND_DOWN mode would result in a value of 3.45. This means that the third decimal place (6 in this case) is ignored and not rounded up.

This rounding mode is also known as truncation or towards zero, as it simply removes any digits beyond the specified scale without rounding them up or down. It is commonly used in financial calculations where precision is important and rounding errors must be minimized.

bigdecimal.ROUND_DOWN与 BigDecimal.ROUND_HALF_UP

`BigDecimal.ROUND_DOWN` 和 `BigDecimal.ROUND_HALF_UP` 是 Java 中 `BigDecimal` 类中的常量，用于控制 `BigDecimal` 对象的舍入行为。

`BigDecimal.ROUND_DOWN` 表示直接截断小数部分，不做四舍五入，例如：

new BigDecimal("3.1415926").setScale(2, BigDecimal.ROUND_DOWN) // 输出 3.14

`BigDecimal.ROUND_HALF_UP` 表示四舍五入，例如：

new BigDecimal("3.1415926").setScale(2, BigDecimal.ROUND_HALF_UP) // 输出 3.14
new BigDecimal("3.1455926").setScale(2, BigDecimal.ROUND_HALF_UP) // 输出 3.15

需要注意的是，`BigDecimal` 的舍入行为是有一定精度误差的，因此在做数值计算时需要谨慎处理。