如何在Java中格式化双输入而不进行舍入？ [英] How do I format double input in Java WITHOUT rounding it?

问题描述

我已经阅读了这个问题将一个小数加倍到2位小数它显示了如何舍入数字。我想要的只是简单的格式化，只打印两个小数位。
我有什么和我尝试过的：

  double res = 24.695999999999998; 
 DecimalFormat df = new DecimalFormat（#### 0.00）; 
 System.out.println（Value：+ df.format（res））; //打印24.70，我想要24.69 
 System.out.println（Total：+ String.format（％。2f，res））; //打印24.70 
  

所以当我有24.695999999999998时我想将其格式化为24.69

解决方案

您需要首先获取double值的 floor - 然后格式化它。 / p>

Math.floor（double）

返回最大（最接近正无穷大）双精度值小于或等于参数且等于数学整数。

所以使用类似：

  double v = Math.floor（res * 100）/ 100.0; 
  

其他替代方案包括使用 BigDecimal 。

  public void test（）{
 double d = 0.29; 
 System.out.println（d =+ d）; 
 System.out.println（floor（d * 100）/ 100 =+ Math.floor（d * 100）/ 100）; 
 System.out.println（BigDecimal d =+ BigDecimal.valueOf（d）.movePointRight（2）.round（MathContext.UNLIMITED）.movePointLeft（2））; 
} 
  

打印

  d = 0.29 
楼（d * 100）/100=0.28 
 BigDecimal d = 0.29 
  

I have read this question Round a double to 2 decimal places It shows how to round number. What I want is just simple formatting, printing only two decimal places. What I have and what I tried:

double res = 24.695999999999998;
DecimalFormat df = new DecimalFormat("####0.00");
System.out.println("Value: " + df.format(res)); //prints 24.70 and I want 24.69
System.out.println("Total: " + String.format( "%.2f", res )); //prints 24.70

So when I have 24.695999999999998 I want to format it as 24.69

解决方案

You need to take the floor of the double value first - then format it.

Math.floor(double)

Returns the largest (closest to positive infinity) double value that is less than or equal to the argument and is equal to a mathematical integer.

So use something like:

double v = Math.floor(res * 100) / 100.0;

Other alternatives include using BigDecimal.

public void test() {
    double d = 0.29;
    System.out.println("d=" + d);
    System.out.println("floor(d*100)/100=" + Math.floor(d * 100) / 100);
    System.out.println("BigDecimal d=" + BigDecimal.valueOf(d).movePointRight(2).round(MathContext.UNLIMITED).movePointLeft(2));
}

prints

d=0.29
floor(d*100)/100=0.28
BigDecimal d=0.29

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