What's the best practice to round a float to 2 decimals?
本问题已经有最佳答案,请猛点这里访问。
我正在使用Eclipse+Android SDK。
我需要把一个浮点值四舍五入到2位小数。我通常使用下一个"技巧"使用数学库。
1 2 3 | float accelerometerX = accelerometerX * 100; accelerometerX = round(accelerometerX); Log.d("Test","" + accelerometerX/100); |
但我觉得这不是最好的方法。
是否有一个库来执行这些类型的操作?
事先谢谢。
2年前我在Java中使用统计学,我仍然有一个函数的代码,它允许你把一个数字和你想要的小数相结合。现在你需要两个,但也许你想用3来比较结果,这个函数给了你这个自由。
1 2 3 4 5 6 7 8 9 10 11 12 | /** * 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(); } |
你需要决定你是想把球打进还是打进。在我的示例代码中,我将进行四舍五入。
希望它有帮助。
编辑
如果要在小数为零时保留小数位数(我猜这只是为了向用户显示),只需将函数类型从float更改为bigdecimal,如下所示:
1 2 3 4 5 | 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; } |
然后这样调用函数:
1 2 3 4 |
这将打印:
1 | 2.30 |
让我们测试3种方法:1)
1 2 3 |
2)
1 2 3 4 5 6 7 | 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; } |
3)
1 2 3 | public static float round3(float d, int decimalPlace) { return BigDecimal.valueOf(d).setScale(decimalPlace, BigDecimal.ROUND_HALF_UP).floatValue(); } |
数字是0.23453F我们将测试每个方法100000次迭代。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
1 2 3 4 | double roundTwoDecimals(double d) { DecimalFormat twoDForm = new DecimalFormat("#.##"); return Double.valueOf(twoDForm.format(d)); } |
这是一个较短的实现,与@jav_rock相比
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | /** * 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 |
我尝试支持@ivan stin优秀第二种方法的-ve值。(他的方法主要归功于@ivan stin)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | 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; } |
下面是我试过的测试案例。如果这不涉及其他案件,请告诉我。
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 | @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); } |
这是一个简单的单行解决方案
1 | ((int) ((value + 0.005f) * 100)) / 100f |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 | //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..*/ |