Question

我正在使用eclipse + Android SDK。

我需要将浮点值舍入为2位小数。我通常使用数学库来使用下一个“技巧”。

float accelerometerX = accelerometerX * 100;
    accelerometerX = round(accelerometerX);
    Log.d("Test","" + accelerometerX/100);

但我觉得这不是最好的方法。

是否有图书馆可以进行这些类型的操作？

提前致谢。

Answer 1

我2年前在Java中使用统计数据，我仍然得到一个函数的代码，允许您将数字四舍五入到您想要的小数位数。现在你需要两个，但也许你想用3来比较结果，这个功能给你这个自由。

/**
* Round to certain number of decimals
* 
* @param d
* @param decimalPlace
* @return
*/
public static float round(float d, int decimalPlace) {
    BigDecimal bd = new BigDecimal(Float.toString(d));
    bd = bd.setScale(decimalPlace, BigDecimal.ROUND_HALF_UP);
    return bd.floatValue();
}

您需要决定是否要向上或向下舍入。在我的示例代码中，我正在进行整理。

希望它有所帮助。

修改

如果你想在它们为零时保留小数位数（我想这只是为了向用户显示），你只需要将函数类型从float更改为BigDecimal，如下所示：

public static BigDecimal round(float d, int decimalPlace) { BigDecimal bd = new BigDecimal(Float.toString(d)); bd = bd.setScale(decimalPlace, BigDecimal.ROUND_HALF_UP); return bd; }

然后以这种方式调用函数：

float x = 2.3f; BigDecimal result; result=round(x,2); System.out.println(result);

这将打印：

2.30

Answer 2

让我们测试3种方法：
1）

public static float round2(float number, int scale) {
    int pow = 10;
    for (int i = 1; i < scale; i++)
        pow *= 10;
    float tmp = number * pow;
    return ( (float) ( (int) ((tmp - (int) tmp) >= 0.5f ? tmp + 1 : tmp) ) ) / pow;
}

2）

public static float round3(float d, int decimalPlace) {
    return BigDecimal.valueOf(d).setScale(decimalPlace, BigDecimal.ROUND_HALF_UP).floatValue();
}

3）

Public class SalesSummary {

  public static void main(String[] args) {

    Scanner input = new Scanner(System.in);

    //declarations
    float month;
    float salesAmt ;
    final int SIZE = 12;
    String[] MONTH = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
    float[] sales = new float[SIZE];
    char response;
    float total;
    float avrg;

    do{
      System.out.printIn ("Enter month");
      month = input.nextFloat();
      if (month > 1 || month < 12)
        System.out.printIn ("Invalid month");
      else 
        month = month - 1;
      System.out.printIn ("Enter sales amount");
      salesAmt = input.nextFloat();
      sales[month] = (sales[month] + salesAmt);
      System.out.printIn("Additional data (Y/N)?");
      response = input.next().charAt(0); 
      total = (sales[0] + sales[1] + sales[2] + sales[3] + sales[4] + sales[5] + sales[6] + sales[7] + sales[8] + sales[9] + sales[10] + sales[11]); 
      avrg = (total / SIZE);
    } while (response == 'y');

    for (int x = 0; x < MONTH.length; ++x) {
      System.out.println("Sales for " + MONTH[x] + " is: " + sales[x] + "Total is" + total + "Average is: " + avrg) ;
    }
  }
}

数量是0.23453f
我们将测试每种方法100,000次迭代。

的结果：
时间1 - 18毫秒
时间2 - 1毫秒
时间3 - 378毫秒

在笔记本电脑上测试
Intel i3-3310M CPU 2.4GHz

Answer 3

double roundTwoDecimals(double d) {
  DecimalFormat twoDForm = new DecimalFormat("#.##");
  return Double.valueOf(twoDForm.format(d));
}

Answer 4

与@ Jav_Rock的

相比，这是一个更短的实现

   /**
     * Round to certain number of decimals
     * 
     * @param d
     * @param decimalPlace the numbers of decimals
     * @return
     */

    public static float round(float d, int decimalPlace) {
         return BigDecimal.valueOf(d).setScale(decimalPlace,BigDecimal.ROUND_HALF_UP).floatValue();
    }



    System.out.println(round(2.345f,2));//two decimal digits, //2.35

Answer 5

我试图支持@Ivan Stin优秀第二种方法的-ve值。 （主要归功于@Ivan Stin的方法）

public static float round(float value, int scale) {
    int pow = 10;
    for (int i = 1; i < scale; i++) {
        pow *= 10;
    }
    float tmp = value * pow;
    float tmpSub = tmp - (int) tmp;

    return ( (float) ( (int) (
            value >= 0
            ? (tmpSub >= 0.5f ? tmp + 1 : tmp)
            : (tmpSub >= -0.5f ? tmp : tmp - 1)
            ) ) ) / pow;

    // Below will only handles +ve values
    // return ( (float) ( (int) ((tmp - (int) tmp) >= 0.5f ? tmp + 1 : tmp) ) ) / pow;
}

以下是我尝试过的测试用例。如果没有解决任何其他情况，请告诉我。

@Test
public void testFloatRound() {
    // +ve values
    Assert.assertEquals(0F, NumberUtils.round(0F), 0);
    Assert.assertEquals(1F, NumberUtils.round(1F), 0);
    Assert.assertEquals(23.46F, NumberUtils.round(23.4567F), 0);
    Assert.assertEquals(23.45F, NumberUtils.round(23.4547F), 0D);
    Assert.assertEquals(1.00F, NumberUtils.round(0.49999999999999994F + 0.5F), 0);
    Assert.assertEquals(123.12F, NumberUtils.round(123.123F), 0);
    Assert.assertEquals(0.12F, NumberUtils.round(0.123F), 0);
    Assert.assertEquals(0.55F, NumberUtils.round(0.55F), 0);
    Assert.assertEquals(0.55F, NumberUtils.round(0.554F), 0);
    Assert.assertEquals(0.56F, NumberUtils.round(0.556F), 0);
    Assert.assertEquals(123.13F, NumberUtils.round(123.126F), 0);
    Assert.assertEquals(123.15F, NumberUtils.round(123.15F), 0);
    Assert.assertEquals(123.17F, NumberUtils.round(123.1666F), 0);
    Assert.assertEquals(123.46F, NumberUtils.round(123.4567F), 0);
    Assert.assertEquals(123.87F, NumberUtils.round(123.8711F), 0);
    Assert.assertEquals(123.15F, NumberUtils.round(123.15123F), 0);
    Assert.assertEquals(123.89F, NumberUtils.round(123.8909F), 0);
    Assert.assertEquals(124.00F, NumberUtils.round(123.9999F), 0);
    Assert.assertEquals(123.70F, NumberUtils.round(123.7F), 0);
    Assert.assertEquals(123.56F, NumberUtils.round(123.555F), 0);
    Assert.assertEquals(123.00F, NumberUtils.round(123.00F), 0);
    Assert.assertEquals(123.50F, NumberUtils.round(123.50F), 0);
    Assert.assertEquals(123.93F, NumberUtils.round(123.93F), 0);
    Assert.assertEquals(123.93F, NumberUtils.round(123.9312F), 0);
    Assert.assertEquals(123.94F, NumberUtils.round(123.9351F), 0);
    Assert.assertEquals(123.94F, NumberUtils.round(123.9350F), 0);
    Assert.assertEquals(123.94F, NumberUtils.round(123.93501F), 0);
    Assert.assertEquals(99.99F, NumberUtils.round(99.99F), 0);
    Assert.assertEquals(100.00F, NumberUtils.round(99.999F), 0);
    Assert.assertEquals(100.00F, NumberUtils.round(99.9999F), 0);

    // -ve values
    Assert.assertEquals(-123.94F, NumberUtils.round(-123.93501F), 0);
    Assert.assertEquals(-123.00F, NumberUtils.round(-123.001F), 0);
    Assert.assertEquals(-0.94F, NumberUtils.round(-0.93501F), 0);
    Assert.assertEquals(-1F, NumberUtils.round(-1F), 0);
    Assert.assertEquals(-0.50F, NumberUtils.round(-0.50F), 0);
    Assert.assertEquals(-0.55F, NumberUtils.round(-0.55F), 0);
    Assert.assertEquals(-0.55F, NumberUtils.round(-0.554F), 0);
    Assert.assertEquals(-0.56F, NumberUtils.round(-0.556F), 0);
    Assert.assertEquals(-0.12F, NumberUtils.round(-0.1234F), 0);
    Assert.assertEquals(-0.12F, NumberUtils.round(-0.123456789F), 0);
    Assert.assertEquals(-0.13F, NumberUtils.round(-0.129F), 0);
    Assert.assertEquals(-99.99F, NumberUtils.round(-99.99F), 0);
    Assert.assertEquals(-100.00F, NumberUtils.round(-99.999F), 0);
    Assert.assertEquals(-100.00F, NumberUtils.round(-99.9999F), 0);
}

Answer 6

这是一个简单的单行解决方案

((int) ((value + 0.005f) * 100)) / 100f

Answer 7

//by importing Decimal format we can do...

import java.util.Scanner;
import java.text.DecimalFormat;
public class Average
{
public static void main(String[] args)
{
int sub1,sub2,sub3,total;
Scanner in = new Scanner(System.in);
System.out.print("Enter Subject 1 Marks : ");
sub1 = in.nextInt();
System.out.print("Enter Subject 2 Marks : ");
sub2 = in.nextInt();
System.out.print("Enter Subject 3 Marks : ");
sub3 = in.nextInt();
total = sub1 + sub2 + sub3;
System.out.println("Total Marks of Subjects = " + total);
res = (float)total;
average = res/3;
System.out.println("Before Rounding Decimal.. Average = " +average +"%");
DecimalFormat df = new DecimalFormat("###.##");
System.out.println("After Rounding Decimal.. Average = " +df.format(average)+"%");
}
}
/* Output
Enter Subject 1 Marks : 72
Enter Subject 2 Marks : 42
Enter Subject 3 Marks : 52
Total Marks of Subjects = 166
Before Rounding Decimal.. Average = 55.333332%
After Rounding Decimal.. Average = 55.33%
*/

/* Output
Enter Subject 1 Marks : 98
Enter Subject 2 Marks : 88
Enter Subject 3 Marks : 78
Total Marks of Subjects = 264
Before Rounding Decimal.. Average = 88.0%
After Rounding Decimal.. Average = 88%
*/

/* You can Find Avrerage values in two ouputs before rounding average
And After rounding Average..*/

将浮点数舍入为2位小数的最佳做法是什么？

7 个答案: