Java :: 比较 ronded doubles 不起作用

Question

我想比较两个数字：

-3.123
-3.123456

我将使用 double 来存储它们，我只想考虑 前 3 位小数 ，所以：

import java.math.RoundingMode;
import java.text.DecimalFormat;

public class DecimalComparator {
    public static void main(String[] args) {
        areEqualByThreeDecimalPlaces(-3.123, -3.123456);
    }

    public static boolean areEqualByThreeDecimalPlaces (double one, double two) {
        boolean same = true;

        DecimalFormat df = new DecimalFormat("#.###");
        df.setRoundingMode(RoundingMode.FLOOR);
        System.out.println(df.format(one));
        System.out.println(df.format(two));

        if (df.format(one).equals(df.format(two))) {
            same = true;
            System.out.println("true");
        } else {
            same = false;
            System.out.println("false");
        }
        return same;
    }
}

代码返回我：

-3.123
-3.124
false

为什么第二个数字四舍五入为-3.124？

Answer 1

RoundingMode.FLOOR 将数字向下舍入 - 您的代码适用于正数，但不适用于负数。您需要使用 RoundingMode.DOWN 只删除 N 位后的数字：

df.setRoundingMode(RoundingMode.DOWN);
// Here ------------------------^

Answer 2

Hi its just that when u round off 3.123456 it works the below way when decimal 
places are reduced :

 3.12346
 3.1235
 3.124
 3.12
 3.1 

//commenting the set rounding mode will make it work the way u want.
public static void main (String[] args ) {
        double one =-3.123;
         double two = -3.123456;
        boolean same = true;

        DecimalFormat df = new DecimalFormat("#.###");
        //remove this line
        //df.setRoundingMode(RoundingMode.FLOOR);

        System.out.println(df.format(one));
        System.out.println(df.format(two));

        if (df.format(one).equals(df.format(two))) {
            same = true;
            System.out.println("true");
        } else {
            same = false;
            System.out.println("false");
        }
        System.out.println(same);
    }

Java :: 比较 ronded doubles 不起作用

Java :: comparing ronded doubles doesn't work

java

double

boolean

compare

decimal