Java:为什么 7/-3 是 -2？

Question

为什么在 java 7/-3 中不是 -3？它是-2。我在想除法的结果是四舍五入的。在 python 2 中它是 -3。 java除法还有其他规则吗？

Answer 1

Is there any other rule for division in java?

与往常一样，对于此类问题，您应该转到 Java Language Specification .在这种情况下，相关部分是 15.17.2 :

Integer division rounds toward 0. That is, the quotient produced for operands n and d that are integers after binary numeric promotion (§5.6.2) is an integer value q whose magnitude is as large as possible while satisfying |d ⋅ q| ≤ |n|. Moreover, q is positive when |n| ≥ |d| and n and d have the same sign, but q is negative when |n| ≥ |d| and n and d have opposite signs.

请注意，此“舍入”不是您可能期望的“中点舍入”:例如，-99/50 是 -1。实际上它是 截断 到 0。

至于为什么 Java 选择使用这种方法而 Python 选择取而代之，这可能是您需要询问语言设计者的问题。每个选项在某些情况下都很有用，而在其他情况下则很痛苦。您可能会发现余数运算符在 Python 中的工作方式也不同——这两个决定通常是相关联的，例如(来自 15.17.3 部分):

The remainder operation for operands that are integers after binary numeric promotion (§5.6.2) produces a result value such that (a/b)*b+(a%b) is equal to a.