java - Java十进制格式问题

Question

我写了一个程序，但我不知道应该如何处理十进制格式？我认为我做得对，显然我不能正确地处理十进制格式。有人可以帮我处理十进制格式吗？

这是我的代码:

import java.text.DecimalFormat;
import java.util.*;
public class Mean {
    public static void main(String [] args){
        Scanner s = new Scanner(System.in);
            double[]x = new double[10];
            int i;
            for(i = 0;i < 10; i++){
                x[i] = s.nextDouble();
            }
            double mean = mean(x, i);
            double deviation = var(x);
            System.out.println("The mean is " + mean);
            System.out.println("The standard deviation is " + deviation);
    }
public static double sum(double[] a) {
        double sum = 0.0;
        for (int i = 0; i < a.length; i++) {
            sum += a[i];
        }
        return sum;
    }
    public static double mean(double[]x, double i){
        if (x.length == 0) return Double.NaN;
        double sum = sum(x);
        return sum / x.length;
    }
    public static double var(double[] x) {
        if (x.length == 0) return Double.NaN;
        double avg = mean(x, 10);
        double sum = 0.0;
        for (int i = 0; i < x.length; i++) {
            sum += (x[i] - avg) * (x[i] - avg);
        }
        DecimalFormat myFormatter = new DecimalFormat("#,##0.00");
        return sum / myFormatter.format(Math.sqrt(x.length - 1));

    }
}

Answer 1

尝试这个来格式化你的 double ...我还必须更新你的方法var -

public static String formatDouble(double in) {
  DecimalFormat myFormatter = new DecimalFormat(
      "#,##0.00");
  return myFormatter.format(in);
}

public static double var(double[] x) {
  if (x.length == 0)
    return Double.NaN;
  double avg = mean(x);
  double sum = 0.0;
  for (int i = 0; i < x.length; i++) {
    sum += (x[i] - avg) * (x[i] - avg);
  }
  return sum / Math.sqrt(x.length - 1);
}

public static void main(String[] args) {
  double[] x = new double[] {
    2000.20, 1000.10, 3000.30, 4000.40,5000.50,
    6000.60,7000,70,8000.80,9000.90
  };
  double mean = mean(x);
  double deviation = var(x);
  System.out.println("The mean is "
      + formatDouble(mean));
  System.out.println("The standard deviation is "
      + formatDouble(deviation));
}