java - 为什么最后一个数字不对？

Question

为什么这段代码的输出只有最后一个数字是错误的:

public class Test {
    public static void main(String[] args) {
        System.out.println("Hello world");
        System.out.println("I wounder is the sqaure root of (2*3) the 
                           same as the sqaure root of 2 and 3 multiplied.");
        double squareroot0 = Math.pow(3*2, 0.5);
        double squarroot1 = (Math.pow(3, 0.5) * Math.pow(2, 0.5)); 
        System.out.println("So is it the same?");

        System.out.println("is " + squareroot0 + " the equvielant of " + 
                                               squarroot1 + "?");
        if(squareroot0 == squarroot1) {
            System.out.println("Yes number one and number two are 
                                               the same, Congrats!");
        }else {
            System.out.println("No they are not! ");
        }

        System.out.println(squareroot0);
        System.out.println(squarroot1);


    }
}

输出:

Hello world
I wonder is the sqaure root of (2*3) the same as the sqaure 
root of 2 and 3 multiplied.
So is it the same?
is 2.449489742783178 the equvielant of 2.4494897427831783?
No they are not! 
2.449489742783178
2.4494897427831783

在数学上它们是等价的，那么这是怎么回事呢？

Math.sqrt() 和 Math.pow(,0.5) 一样准确。

Answer 1

您无法在有限的计算机中以无限精度表示数字，因此您需要四舍五入。你看到的是四舍五入的效果。这是所有 float 使用所固有的。

必填链接:What Every Computer Scientist Should Know About Floating-Point Arithmetic