Java中Math.rint()和Math.round()之间的区别 [英] Difference between Math.rint() and Math.round() in Java

问题描述

Math.rint()和 Math.round()有什么区别?

推荐答案

Math.rint()和 Math.round()有一些区别，但其中一个可能对Java应用程序的业务逻辑的影响最大的是它们处理边界上整数的舍入方式(例如， 4.5 位于 4 和 5 ).考虑以下代码片段和输出:

Math.rint() and Math.round() have several differences, but the one which might impact the business logic of a Java application the most is the way they handle rounding of integers which are on a boundary (e.g. 4.5 is on the boundary of 4 and 5). Consider the following code snippet and output:

double val1 = 4.2;
double val2 = 4.5;
System.out.println("Math.rint(" + val1 + ")    = " + Math.rint(val1));
System.out.println("Math.round(" + val1 + ")   = " + Math.round(val1));
System.out.println("Math.rint(" + val2 + ")    = " + Math.rint(val2));
System.out.println("Math.round(" + val2 + ")   = " + Math.round(val2));
System.out.println("Math.rint(" + (val2 + 0.001d) + ")  = " + Math.rint(val2 + 0.001d));
System.out.println("Math.round(" + (val2 + 0.001d) + ") = " + Math.round(val2 + 0.001d));

输出:

Math.rint(4.2)    = 4.0
Math.round(4.2)   = 4
Math.rint(4.5)    = 4.0
Math.round(4.5)   = 5
Math.rint(4.501)  = 5.0
Math.round(4.501) = 5

如您所见， Math.rint(4.5)实际上是四舍五入的，而 Math.round(4.5)则是四舍五入的，这一点值得指出.但是，在所有其他情况下，它们都表现出我们期望的相同舍入规则.

As you can see, Math.rint(4.5) actually rounds down, while Math.round(4.5) rounds up, and this deserves to be pointed out. However, in all other cases, they both exhibit the same rounding rules which we would expect.

这是一篇有用的Code Ranch文章，简要比较了 Math.rint()和 Math.round():

Here is a useful Code Ranch article which briefly compares Math.rint() and Math.round(): http://www.coderanch.com/t/239803/java-programmer-OCPJP/certification/Difference-rint-methods-Math-class

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