Java 如何很好地将浮点数格式化为字符串,而不需要不必要的十进制0';s
64位双精度可以精确表示整数+/-253 鉴于这一事实,我选择使用双精度类型作为所有类型的单一类型,因为我的最大整数是一个无符号32位数字 但现在我必须打印这些伪整数,但问题是它们也与实际的双精度数混合在一起 那么如何在Java中很好地打印这些双精度 我已经尝试了Java 如何很好地将浮点数格式化为字符串,而不需要不必要的十进制0';s,java,string,floating-point,format,double,Java,String,Floating Point,Format,Double,64位双精度可以精确表示整数+/-253 鉴于这一事实,我选择使用双精度类型作为所有类型的单一类型,因为我的最大整数是一个无符号32位数字 但现在我必须打印这些伪整数,但问题是它们也与实际的双精度数混合在一起 那么如何在Java中很好地打印这些双精度 我已经尝试了String.format(“%f”,value),这很接近,只是我得到了很多小值的尾随零 下面是of%f 232.00000000 0.18000000000 1237875192.0 4.5800000000 0.00000000
String.format(“%f”,value)
,这很接近,只是我得到了很多小值的尾随零
下面是of%f
232.00000000
0.18000000000
1237875192.0
4.5800000000
0.00000000
1.23450000
232
0.18000000000
1237875192
4.5800000000
0
1.23450000
我想要的是:
232
0.18
1237875192
4.58
0
1.2345
232
0.18
1237875192
4.58
0
1.2345
当然,我可以编写一个函数来修剪这些零,但由于字符串操作,这会造成很多性能损失。我能用其他格式代码做得更好吗
Tom E.和Jeremy S.的答案是不可接受的,因为他们都任意四舍五入到小数点后两位。回答前请先理解问题
请注意,
String.format(format,args…
取决于地区设置(请参见下面的答案)。不,没关系。字符串操作导致的性能损失为零
下面是在%f
之后修剪末端的代码:
private static String trimTrailingZeros(String number) {
if(!number.contains(".")) {
return number;
}
return number.replaceAll("\\.?0*$", "");
}
正如评论中所指出的,这不是对原始问题的正确答案。这就是说,这是一种非常有用的方法,可以格式化数字,而不需要不必要的尾随零
String s = "1.210000";
while (s.endsWith("0")){
s = (s.substring(0, s.length() - 1));
}
这将使字符串以0-s的速度落下尾部。最好的方法如下:
public class Test {
public static void main(String args[]){
System.out.println(String.format("%s something", new Double(3.456)));
System.out.println(String.format("%s something", new Double(3.456234523452)));
System.out.println(String.format("%s something", new Double(3.45)));
System.out.println(String.format("%s something", new Double(3)));
}
}
输出:
3.456什么的
3.45623452什么的
3.45什么
3.0什么的
唯一的问题是最后一个没有删除.0的问题。但如果你能接受这一点,那么这是最好的。2f将其四舍五入到最后两位小数。决策格式也是如此。如果您需要所有的小数位,但不需要尾随的零,那么这是最好的方法。我制作了一个
DoubleFormatter
来有效地将大量的双精度值转换为一个漂亮的/可呈现的字符串:
double horribleNumber = 3598945.141658554548844;
DoubleFormatter df = new DoubleFormatter(4, 6); // 4 = MaxInteger, 6 = MaxDecimal
String beautyDisplay = df.format(horribleNumber);
- 如果V的整数部分大于MaxInteger=>以科学格式显示V(1.2345E+30)。否则,以正常格式显示(124.45678)
- MaxDecimal决定小数位数(修剪为)
import java.math.RoundingMode;
import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import java.text.NumberFormat;
import java.util.Locale;
import com.google.common.base.Preconditions;
import com.google.common.base.Strings;
/**
* Convert a double to a beautiful String (US-local):
*
* double horribleNumber = 3598945.141658554548844;
* DoubleFormatter df = new DoubleFormatter(4,6);
* String beautyDisplay = df.format(horribleNumber);
* String beautyLabel = df.formatHtml(horribleNumber);
*
* Manipulate 3 instances of NumberFormat to efficiently format a great number of double values.
* (avoid to create an object NumberFormat each call of format()).
*
* 3 instances of NumberFormat will be reused to format a value v:
*
* if v < EXP_DOWN, uses nfBelow
* if EXP_DOWN <= v <= EXP_UP, uses nfNormal
* if EXP_UP < v, uses nfAbove
*
* nfBelow, nfNormal and nfAbove will be generated base on the precision_ parameter.
*
* @author: DUONG Phu-Hiep
*/
public class DoubleFormatter
{
private static final double EXP_DOWN = 1.e-3;
private double EXP_UP; // always = 10^maxInteger
private int maxInteger_;
private int maxFraction_;
private NumberFormat nfBelow_;
private NumberFormat nfNormal_;
private NumberFormat nfAbove_;
private enum NumberFormatKind {Below, Normal, Above}
public DoubleFormatter(int maxInteger, int maxFraction){
setPrecision(maxInteger, maxFraction);
}
public void setPrecision(int maxInteger, int maxFraction){
Preconditions.checkArgument(maxFraction>=0);
Preconditions.checkArgument(maxInteger>0 && maxInteger<17);
if (maxFraction == maxFraction_ && maxInteger_ == maxInteger) {
return;
}
maxFraction_ = maxFraction;
maxInteger_ = maxInteger;
EXP_UP = Math.pow(10, maxInteger);
nfBelow_ = createNumberFormat(NumberFormatKind.Below);
nfNormal_ = createNumberFormat(NumberFormatKind.Normal);
nfAbove_ = createNumberFormat(NumberFormatKind.Above);
}
private NumberFormat createNumberFormat(NumberFormatKind kind) {
// If you do not use the Guava library, replace it with createSharp(precision);
final String sharpByPrecision = Strings.repeat("#", maxFraction_);
NumberFormat f = NumberFormat.getInstance(Locale.US);
// Apply bankers' rounding: this is the rounding mode that
// statistically minimizes cumulative error when applied
// repeatedly over a sequence of calculations
f.setRoundingMode(RoundingMode.HALF_EVEN);
if (f instanceof DecimalFormat) {
DecimalFormat df = (DecimalFormat) f;
DecimalFormatSymbols dfs = df.getDecimalFormatSymbols();
// Set group separator to space instead of comma
//dfs.setGroupingSeparator(' ');
// Set Exponent symbol to minus 'e' instead of 'E'
if (kind == NumberFormatKind.Above) {
dfs.setExponentSeparator("e+"); //force to display the positive sign in the exponent part
} else {
dfs.setExponentSeparator("e");
}
df.setDecimalFormatSymbols(dfs);
// Use exponent format if v is outside of [EXP_DOWN,EXP_UP]
if (kind == NumberFormatKind.Normal) {
if (maxFraction_ == 0) {
df.applyPattern("#,##0");
} else {
df.applyPattern("#,##0."+sharpByPrecision);
}
} else {
if (maxFraction_ == 0) {
df.applyPattern("0E0");
} else {
df.applyPattern("0."+sharpByPrecision+"E0");
}
}
}
return f;
}
public String format(double v) {
if (Double.isNaN(v)) {
return "-";
}
if (v==0) {
return "0";
}
final double absv = Math.abs(v);
if (absv<EXP_DOWN) {
return nfBelow_.format(v);
}
if (absv>EXP_UP) {
return nfAbove_.format(v);
}
return nfNormal_.format(v);
}
/**
* Format and higlight the important part (integer part & exponent part)
*/
public String formatHtml(double v) {
if (Double.isNaN(v)) {
return "-";
}
return htmlize(format(v));
}
/**
* This is the base alogrithm: create a instance of NumberFormat for the value, then format it. It should
* not be used to format a great numbers of value
*
* We will never use this methode, it is here only to understanding the Algo principal:
*
* format v to string. precision_ is numbers of digits after decimal.
* if EXP_DOWN <= abs(v) <= EXP_UP, display the normal format: 124.45678
* otherwise display scientist format with: 1.2345e+30
*
* pre-condition: precision >= 1
*/
@Deprecated
public String formatInefficient(double v) {
// If you do not use Guava library, replace with createSharp(precision);
final String sharpByPrecision = Strings.repeat("#", maxFraction_);
final double absv = Math.abs(v);
NumberFormat f = NumberFormat.getInstance(Locale.US);
// Apply bankers' rounding: this is the rounding mode that
// statistically minimizes cumulative error when applied
// repeatedly over a sequence of calculations
f.setRoundingMode(RoundingMode.HALF_EVEN);
if (f instanceof DecimalFormat) {
DecimalFormat df = (DecimalFormat) f;
DecimalFormatSymbols dfs = df.getDecimalFormatSymbols();
// Set group separator to space instead of comma
dfs.setGroupingSeparator(' ');
// Set Exponent symbol to minus 'e' instead of 'E'
if (absv>EXP_UP) {
dfs.setExponentSeparator("e+"); //force to display the positive sign in the exponent part
} else {
dfs.setExponentSeparator("e");
}
df.setDecimalFormatSymbols(dfs);
//use exponent format if v is out side of [EXP_DOWN,EXP_UP]
if (absv<EXP_DOWN || absv>EXP_UP) {
df.applyPattern("0."+sharpByPrecision+"E0");
} else {
df.applyPattern("#,##0."+sharpByPrecision);
}
}
return f.format(v);
}
/**
* Convert "3.1416e+12" to "<b>3</b>.1416e<b>+12</b>"
* It is a html format of a number which highlight the integer and exponent part
*/
private static String htmlize(String s) {
StringBuilder resu = new StringBuilder("<b>");
int p1 = s.indexOf('.');
if (p1>0) {
resu.append(s.substring(0, p1));
resu.append("</b>");
} else {
p1 = 0;
}
int p2 = s.lastIndexOf('e');
if (p2>0) {
resu.append(s.substring(p1, p2));
resu.append("<b>");
resu.append(s.substring(p2, s.length()));
resu.append("</b>");
} else {
resu.append(s.substring(p1, s.length()));
if (p1==0){
resu.append("</b>");
}
}
return resu.toString();
}
}
import java.math.RoundingMode;
导入java.text.DecimalFormat;
导入java.text.DecimalFormatSymbols;
导入java.text.NumberFormat;
导入java.util.Locale;
导入com.google.common.base.premissions;
导入com.google.common.base.Strings;
/**
*将双精度转换为漂亮的字符串(美国本地):
*
*双倍数字=3598945.1416585548844;
*双格式化程序df=新的双格式化程序(4,6);
*字符串beautyDisplay=df.format(horribleNumber);
*字符串beautyLabel=df.formatHtml(horribleNumber);
*
*操作NumberFormat的3个实例以有效地格式化大量的双精度值。
*(避免在每次调用format()时创建对象编号格式)。
*
*将重用NumberFormat的3个实例来格式化值v:
*
*如果v0){
结果追加(s.子串(0,p1));
结果追加(“”);
}否则{
p1=0;
}
int p2=s.lastIndexOf('e');
如果(p2>0){
结果追加(s.子串(p1,p2));
结果追加(“”);
结果追加(s.substring(p2,s.length());
结果追加(“”);
}否则{
结果追加(s.substring(p1,s.length());
如果(p1==0){
结果追加(“”);
}
}
返回resu.toString();
}
}
注意:我使用了库中的两个函数。如果您不使用番石榴,请自己编写代码:
/**
* Equivalent to Strings.repeat("#", n) of the Guava library:
*/
private static String createSharp(int n) {
StringBuilder sb = new StringBuilder();
for (int i=0; i<n; i++) {
sb.append('#');
}
return sb.toString();
}
/**
*相当于字符串。重复番石榴库中的(“#”),n):
*/
私有静态字符串createSharp(int n){
StringBuilder sb=新的StringBuilder();
对于(int i=0;i,如果想法是打印存储为双精度的整数,就像它们是整数一样,否则以最低必要精度打印双精度:
public static String fmt(double d)
{
if(d == (long) d)
return String.format("%d",(long)d);
else
return String.format("%s",d);
}
产生:
232
0.18
1237875192
4.58
0
1.2345
232
0.18
1237875192
4.58
0
1.2345
并且不依赖于字符串操作。这里有两种方法可以实现它。首先,更短(可能更好)的方法:
String s = String.valueof("your int variable");
while (g.endsWith("0") && g.contains(".")) {
g = g.substring(0, g.length() - 1);
if (g.endsWith("."))
{
g = g.substring(0, g.length() - 1);
}
}
这是一个较长的、可能更糟的方法:
public static String formatFloatToString(final float f)
{
final String s = Float.toString(f);
int dotPos = -1;
for(int i=0; i<s.length(); ++i)
if(s.charAt(i) == '.')
{
dotPos = i;
break;
}
if(dotPos == -1)
return s;
int end = dotPos;
for(int i = dotPos + 1; i<s.length(); ++i)
{
final char c = s.charAt(i);
if(c != '0')
end = i + 1;
}
final String result = s.substring(0, end);
return result;
}
公共静态字符串格式floatToString(最终浮点f)
{
最后一个字符串s=Float.toString(f);
int dotPos=-1;
对于(int i=0;i这里有一个实际有效的答案(这里是不同答案的组合)
在我的机器上,以下函数大约比提供的函数快7倍,因为它避免了String.format
:
public static String prettyPrint(double d) {
int i = (int) d;
return d == i ? String.valueOf(i) : String.valueOf(d);
}
简而言之:
如果要消除尾随零和问题,则应使用:
double myValue = 0.00000021d;
DecimalFormat df = new DecimalFormat("0", DecimalFormatSymbols.getInstance(Locale.ENGLISH));
df.setMaximumFractionDigits(340); //340 = DecimalFormat.DOUBLE_FRACTION_DIGITS
System.out.println(df.format(myValue)); //output: 0.00000021
说明:
为什么其他答案不适合我:
Double.toString()
或System.out.println
或FloatingDecimal.toJavaFormatString
使用科学符号
public static String removeTrailingZeros(double f)
{
if(f == (int)f) {
return String.format("%d", (int)f);
}
return String.format("%f", f).replaceAll("0*$", "");
}
public static String prettyPrint(double d) {
int i = (int) d;
return d == i ? String.valueOf(i) : String.valueOf(d);
}
double myValue = 0.00000021d;
DecimalFormat df = new DecimalFormat("0", DecimalFormatSymbols.getInstance(Locale.ENGLISH));
df.setMaximumFractionDigits(340); //340 = DecimalFormat.DOUBLE_FRACTION_DIGITS
System.out.println(df.format(myValue)); //output: 0.00000021
double myValue = 0.00000021d;
String.format("%s", myvalue); //output: 2.1E-7
double myValue = 0.00000021d;
String.format("%.12f", myvalue); // Output: 0.000000210000
double myValue = 0.00000021d;
System.out.println(String.format("%.0f", myvalue)); // Output: 0
DecimalFormat df = new DecimalFormat("0");
System.out.println(df.format(myValue)); // Output: 0
double myValue = 0.00000021d;
DecimalFormat df = new DecimalFormat("0");
df.setMaximumFractionDigits(340);
System.out.println(df.format(myvalue)); // Output: 0,00000021
if (d % 1.0 != 0)
return String.format("%s", d);
else
return String.format("%.0f", d);
0.12
12
12.144252
0
double f = 123456.789d;
System.out.println(String.format(Locale.FRANCE,"%f",f));
System.out.println(String.format(Locale.GERMANY,"%f",f));
System.out.println(String.format(Locale.US,"%f",f));
123456,789000
123456,789000
123456.789000
res += stripFpZeroes(String.format((Locale) null, (nDigits!=0 ? "%."+nDigits+"f" : "%f"), value));
...
protected static String stripFpZeroes(String fpnumber) {
int n = fpnumber.indexOf('.');
if (n == -1) {
return fpnumber;
}
if (n < 2) {
n = 2;
}
String s = fpnumber;
while (s.length() > n && s.endsWith("0")) {
s = s.substring(0, s.length()-1);
}
return s;
}
import java.util.ArrayList;
import java.util.List;
public class UseMixedNumbers {
public static void main(String[] args) {
List<Number> listNumbers = new ArrayList<Number>();
listNumbers.add(232);
listNumbers.add(0.18);
listNumbers.add(1237875192);
listNumbers.add(4.58);
listNumbers.add(0);
listNumbers.add(1.2345);
for (Number number : listNumbers) {
System.out.println(number);
}
}
}
232
0.18
1237875192
4.58
0
1.2345
if (d == Math.floor(d)) {
return String.format("%.0f", d); //Format is: 0 places after decimal point
} else {
return Double.toString(d);
}
if(n % 1 == 0) {
return String.format(Locale.US, "%.0f", n));
} else {
return String.format(Locale.US, "%.1f", n));
}
public static String removeZero(double number) {
DecimalFormat format = new DecimalFormat("#.###########");
return format.format(number);
}
new DecimalFormat("00.#").format(20.236)
//out =20.2
new DecimalFormat("00.#").format(2.236)
//out =02.2
public static String fmt(double d) {
String val = Double.toString(d);
String[] valArray = val.split("\\.");
long valLong = 0;
if(valArray.length == 2) {
valLong = Long.parseLong(valArray[1]);
}
if (valLong == 0)
return String.format("%d", (long) d);
else
return String.format("%s", d);
}
private static String format(final double dbl) {
return dbl % 1 != 0 ? String.valueOf(dbl) : String.valueOf((int) dbl);
}
/**
* 23.0 -> $23
*
* 23.1 -> $23.1
*
* 23.01 -> $23.01
*
* 23.99 -> $23.99
*
* 23.999 -> $24
*
* -0.0 -> $0
*
* -5.00 -> -$5
*
* -5.019 -> -$5.02
*/
fun Double?.formatUserAsSum(): String {
return when {
this == null || this == 0.0 -> "$0"
this % 1 == 0.0 -> DecimalFormat("$#,##0;-$#,##0").format(this)
else -> DecimalFormat("$#,##0.##;-$#,##0.##").format(this)
}
}
var yourDouble: Double? = -20.00
println(yourDouble.formatUserAsSum()) // will print -$20
yourDouble = null
println(yourDouble.formatUserAsSum()) // will print $0
fun Double.toPrettyString() =
if(this - this.toLong() == 0.0)
String.format("%d", this.toLong())
else
String.format("%s", this)
float price = 4.30;
DecimalFormat format = new DecimalFormat("0.##"); // Choose the number of decimal places to work with in case they are different than zero and zero value will be removed
format.setRoundingMode(RoundingMode.DOWN); // Choose your Rounding Mode
System.out.println(format.format(price));
4.30 => 4.3
4.39 => 4.39 // Choose format.setRoundingMode(RoundingMode.UP) to get 4.4
4.000000 => 4
4 => 4
/**
* Example: (isDecimalRequired = true)
* d = 12345
* returns 12,345.00
*
* d = 12345.12345
* returns 12,345.12
*
* ==================================================
* Example: (isDecimalRequired = false)
* d = 12345
* returns 12,345 (notice that there's no decimal since it's zero)
*
* d = 12345.12345
* returns 12,345.12
*
* @param d float to format
* @param zeroCount number decimal places
* @param isDecimalRequired true if it will put decimal even zero,
* false will remove the last decimal(s) if zero.
*/
fun formatDecimal(d: Float? = 0f, zeroCount: Int, isDecimalRequired: Boolean = true): String {
val zeros = StringBuilder()
for (i in 0 until zeroCount) {
zeros.append("0")
}
var pattern = "#,##0"
if (zeros.isNotEmpty()) {
pattern += ".$zeros"
}
val numberFormat = DecimalFormat(pattern)
var formattedNumber = if (d != null) numberFormat.format(d) else "0"
if (!isDecimalRequired) {
for (i in formattedNumber.length downTo formattedNumber.length - zeroCount) {
val number = formattedNumber[i - 1]
if (number == '0' || number == '.') {
formattedNumber = formattedNumber.substring(0, formattedNumber.length - 1)
} else {
break
}
}
}
return formattedNumber
}
/**
* Formats the given Number as with as many fractional digits as precision
* available.<br>
* This is a convenient method in case all fractional digits shall be
* rendered and no custom format / pattern needs to be provided.<br>
* <br>
* This serves as a workaround for {@link NumberFormat#getNumberInstance()}
* which by default only renders up to three fractional digits.
*
* @param number
* @param locale
* @param groupingUsed <code>true</code> if grouping shall be used
*
* @return
*/
public static String formatNumberFraction(final Number number, final Locale locale, final boolean groupingUsed)
{
if (number == null)
return null;
final BigDecimal bDNumber = MathUtils.getBigDecimal(number);
final NumberFormat numberFormat = NumberFormat.getNumberInstance(locale);
numberFormat.setMaximumFractionDigits(Math.max(0, bDNumber.scale()));
numberFormat.setGroupingUsed(groupingUsed);
// Convert back for locale percent formatter
return numberFormat.format(bDNumber);
}
/**
* Formats the given Number as percent with as many fractional digits as
* precision available.<br>
* This is a convenient method in case all fractional digits shall be
* rendered and no custom format / pattern needs to be provided.<br>
* <br>
* This serves as a workaround for {@link NumberFormat#getPercentInstance()}
* which does not renders fractional digits.
*
* @param number Number in range of [0-1]
* @param locale
*
* @return
*/
public static String formatPercentFraction(final Number number, final Locale locale)
{
if (number == null)
return null;
final BigDecimal bDNumber = MathUtils.getBigDecimal(number).multiply(new BigDecimal(100));
final NumberFormat percentScaleFormat = NumberFormat.getPercentInstance(locale);
percentScaleFormat.setMaximumFractionDigits(Math.max(0, bDNumber.scale() - 2));
final BigDecimal bDNumberPercent = bDNumber.multiply(new BigDecimal(0.01));
// Convert back for locale percent formatter
final String strPercent = percentScaleFormat.format(bDNumberPercent);
return strPercent;
}