如何限制双数打印的小数位数？ [英] How do I limit the number of decimals printed for a double?

问题描述

这个程序可以工作，除了nJars的数量是7的倍数之外，我会得到一个答案，如$ 14.999999999999998。 6，输出为14.08。如何修复7的倍数的异常，这样会显示$ 14.99？

  import java.util.Scanner; 
 public class Homework_17 
 {
 private static int nJars，nCartons，totalOunces，OuncesTolbs，lbs; 
 
 public static void main（String [] args）
 {
 computeShippingCost（）; 
} 
 
 public static void computeShippingCost（）
 {
 System.out.print（输入一些jar：）; 
扫描仪kboard =新扫描仪（System.in）; 
 nJars = kboard.nextInt（）; 
 int nCartons =（nJars + 11）/ 12; 
 int totalOunces =（nJars * 21）+（nCartons * 25）; 
 int lbs = totalOunces / 16; 
 double shippingCost =（（nCartons * 1.44）+（lbs + 1）* 0.96）+ 3.0; 
 
 System.out.print（$+ shippingCost）; 
} 
} 
  

解决方案

使用 DecimalFormatter ：

  double number = 0.9999999999999; 
 DecimalFormat numberFormat = new DecimalFormat（＃。00）; 
 System.out.println（numberFormat.format（number））; 
  

会给你0.99。您可以在右侧添加或减去0以获得更多或更少的小数。或者在右边使用'＃'，使额外的数字可以选择，如＃。##（0.30）会将尾随0的值降至（0.3） 。

This program works, except when the number of nJars is a multiple of 7, I will get an answer like $14.999999999999998. For 6, the output is 14.08. How do I fix exceptions for multiples of 7 so it will display something like $14.99?

import java.util.Scanner;
public class Homework_17
{
 private static int nJars, nCartons, totalOunces, OuncesTolbs, lbs;

 public static void main(String[] args)
  {
   computeShippingCost();
  }

  public static void computeShippingCost()
  {
   System.out.print("Enter a number of jars: ");
   Scanner kboard = new Scanner (System.in);
   nJars = kboard.nextInt();
   int nCartons = (nJars + 11) / 12;
   int totalOunces = (nJars * 21) + (nCartons * 25);
   int lbs = totalOunces / 16;
   double shippingCost =  ((nCartons * 1.44) + (lbs + 1) * 0.96) + 3.0;

   System.out.print("$" + shippingCost);
   }
}

解决方案

Use a DecimalFormatter:

double number = 0.9999999999999;
DecimalFormat numberFormat = new DecimalFormat("#.00");
System.out.println(numberFormat.format(number));

Will give you "0.99". You can add or subtract 0 on the right side to get more or less decimals.

Or use '#' on the right to make the additional digits optional, as in with #.## (0.30) would drop the trailing 0 to become (0.3).

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