Java Double 与 BigDecimal

Question

我正在查看一些使用 double 变量来存储 (360-359.9998779296875) 结果的代码，即 0.0001220703125。 double 变量将其存储为 -1.220703125E-4。当我使用 BigDecimal 时，它存储为 0.0001220703125。为什么将其双重存储为-1.220703125E-4？

Answer 1

我不会在这里提及精度问题，而只会提及数字的打印方式。

如 javadoc of Double#toString 中所述:

If m is less than 10^-3 or greater than or equal to 10^7, then it is represented in so-called "computerized scientific notation."

而the javadoc of BigDecimal#toString :

If the scale is greater than or equal to zero and the adjusted exponent is greater than or equal to -6, the number will be converted to a character form without using exponential notation

您可以尝试这个小程序来检查各种输出格式，特别是，表示法从标准记数法切换到科学记数法的阈值在两个类中是不同的。

输出:

0.5                         0.5
3.0517578125E-5             0.000030517578125
9.5367431640625E-7          9.5367431640625E-7

代码:

public static void main(String args[]) {
    //trying to use numbers with an exact double representation
    double d1 = 0.5;
    double d2 = 0.000030517578125;
    double d3 = 0.00000095367431640625;

    BigDecimal bd1 = new BigDecimal(d1);
    BigDecimal bd2 = new BigDecimal(d2);
    BigDecimal bd3 = new BigDecimal(d3);

    System.out.println(d1 + "\t\t\t" + bd1);
    System.out.println(d2 + "\t\t" + bd2);
    System.out.println(d3 + "\t" + bd3);
}