Java run-off error(on float and double)

来源：互联网发布：大数据魔镜编辑：程序博客网时间：2024/05/17 08:29

We can't store real 3.9 in Base 2.

double a = 3.9;boolean b = false;if(a == 3.9){   b = true;}System.out.println(b);

输出为：

false

(3.9)Base 10 = (1 1 . 1 1 1 00 1 1......)Base 2

2^1 2^0 2^-1 2^-2 2^-3 ... 2^-6 2^-7 ...

1/2 1/4 1/8 1/64 1/128

≈ 3 +0.8984375...

∴ We can not store real 3.9 in Base 2.

Example 1:

public class FloatingPointError {public static void main(String[] args) {double x = 3.9;double y = 3.8; double difference = x - y;System.out.println(difference);if (difference == 0.1) {System.out.println("I can do simple math.");} else {System.out.println("I am having trouble with easy problems.");}}}

输出为：

0.10000000000000009I am having trouble with easy problems.

我们可以通过“epsilon”（极小的正数）来检测是否x = 3.9。

Example 2:

public class FloatingPointDoneRight {public static void main(String[] args) {double EPSILON = 0.00000000001;double x = 3.9;double y = 3.8;double difference = x - y;if (Math.abs(difference - 0.1) < EPSILON) {System.out.println("I can do simple math.");} else {System.out.println("I am having trouble with easy problems.");}}}

输出为：

I can do simple math.

阅读全文

'); })();