有时候下载的文件/文件夹会带有广告后缀，通过Java实现批量去除

读《Effective Java》Item 60 : Avoid float and double if exact answers are required的时候，结尾写BigDecimal的优点时写道

Using BigDecimal has the added advantage that it gives you full control over rounding, letting you select from eight rounding modes whenever an operation that entails rounding is performed.

这里的eight rounding modes（八种舍入模式）第一次看到，查找资料记录一下