java - 返回数据不带两位小数 :Rounding Doubles

Question

我是 Java 编程的新手，我需要帮助将 double[] arrayP 或问题的百分比四舍五入到小数点后两位。对于程序本身的任何反馈也非常感谢。

谢谢!

It looks like this:
Sum Frequency   Percentage
2   1042        2.8944444444444444
3   2003        5.563888888888889
4   3032        8.422222222222222
5   3953        10.980555555555556
6   4971        13.808333333333334
7   6020        16.72222222222222
8   4986        13.850000000000001
9   4022        11.172222222222222
10  2979        8.275
11  1988        5.522222222222222
12  1003        2.786111111111111

Should look like this:
Sum Frequency Percentage
2   1034      2.87
3   1987      5.52
4   3028      8.41
5   3881      10.78
6   4912      13.64
7   6135      17.04
8   5060      14.06
9   4032      11.20
10  2965      8.24
11  2003      5.56
12  963       2.68

这是我的代码:

public class Assignment_Roll36 {
    public static void main(String[] args) {
        //create table
        System.out.println("Sum\t" + "Frequency" + "\tPercentage");

        //create an array to store sum
        int[] arraySum = new int[35999];

        //counters
        int[] sumFreq = {0,0,0,0,0,0,0,0,0,0,0};


        //loop for dice & sum & storage in array
                for(int i = 0; i < 35999; i++){
                //create random roll dice1 & dice2
                int dice1 = (int)(Math.random() * 6 + 1);
                int dice2 = (int)(Math.random() * 6 + 1);
                //sum for dice 1 & dice2
                int sum = dice1 + dice2; 
                //store sum into array 
                arraySum[i] = sum;

                //if to send to counter
                    if (arraySum[i] == 2) {
                        sumFreq[0]++;
                    } else if (arraySum[i] == 3) {
                        sumFreq[1]++;
                    } else if (arraySum[i] == 4) {
                        sumFreq[2]++;
                    } else if (arraySum[i] == 5) {
                        sumFreq[3]++;
                    } else if (arraySum[i] == 6) {
                        sumFreq[4]++;
                    } else if (arraySum[i] == 7) {
                        sumFreq[5]++;
                    } else if (arraySum[i] == 8) {
                        sumFreq[6]++;
                    } else if (arraySum[i] == 9) {
                        sumFreq[7]++;
                    } else if (arraySum[i] == 10) {
                        sumFreq[8]++;
                    } else if (arraySum[i] == 11) {
                        sumFreq[9]++;
                    } else if (arraySum[i] == 12) {
                        sumFreq[10]++;
                    }
                }

        **double[] arrayP = new double[11];
        for (int a=0;a<11; a++){
            double total = 36000;
            double value = (sumFreq[a] / total);
            double percent = value * 100;
            arrayP[a] = percent;**

        }




        //for loop ends
        int[] array1 = {2,3,4,5,6,7,8,9,10,11,12};
        for(int y = 0; y < 11; y++){
            System.out.println(array1[y] + "\t" + sumFreq[y] + "\t\t" + arrayP[y]);

        }

                } 
    }

Answer 1

存储 的值与打印 的视觉表示之间存在差异(在这种情况下，您的System.out.println调用)。

一般来说，您希望在代码中保持数据的精确性，然后根据需要对其进行格式化以便打印。对于 double ，您可以使用类似的东西:

DecimalFormat df = new DecimalFormat("#.##");
System.out.println("Value is " + df.format(value));