为什么从 float 转换为 double 会改变值?

Why converting from float to double changes the value?(为什么从 float 转换为 double 会改变值?)

问题描述

我一直在试图找出原因，但我找不到.有人可以帮帮我吗?

I've been trying to find out the reason, but I couldn't. Can anybody help me?

看下面的例子.

float f = 125.32f;
System.out.println("value of f = " + f);
double d = (double) 125.32f; 
System.out.println("value of d = " + d);

这是输出:

value of f = 125.32
value of d = 125.31999969482422

推荐答案

float 的值在转换为 double 时不会改变.显示的数字有所不同，因为需要更多数字来区分 double 值与其相邻值，即 Java 文档要求.那是 toString 的文档，从 println 的文档中引用(通过几个链接).

The value of a float does not change when converted to a double. There is a difference in the displayed numerals because more digits are required to distinguish a double value from its neighbors, which is required by the Java documentation. That is the documentation for toString, which is referred (through several links) from the documentation for println.

125.32f 的确切值是 125.31999969482421875.两个相邻的 float 值是 125.3199920654296875 和 125.32000732421875.观察到 125.32 比任何一个邻居都更接近 125.31999969482421875.因此，通过显示125.32"，Java 显示了足够的数字，以便从十进制数字转换回 float 再现了传递给 println<的 float 的值/代码>.