不，没关系。由于字符串操作造成的性能损失为零。

下面是修饰%f后面结尾的代码:

private static String trimTrailingZeros(String number) {
    if(!number.contains(".")) {
        return number;
    }

    return number.replaceAll("\\.?0*$", "");
}

String.format("%.2f", value);

String s = "1.210000";
while (s.endsWith("0")){
    s = (s.substring(0, s.length() - 1));
}

这将使字符串丢弃0-s尾。

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 something
3.456234523452 something
3.45 something
3.0 something

唯一的问题是最后一个。0没有被删除。但如果你能接受这一点，那么这种方法就最好了。%。2f会四舍五入到小数点后两位。DecimalFormat也是如此。如果你需要所有的小数点后数位，但不需要后面的零，那么这个方法是最好的。

我做了一个DoubleFormatter来有效地将大量的double值转换为一个漂亮/像样的字符串:

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 =>，则以科学格式(1.2345E+30)显示V。否则，以正常格式(124.45678)显示。 MaxDecimal决定十进制数字的数量(与银行家的四舍五入修剪)

代码如下:

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();
    }
}

注意:我使用了Guava库中的两个函数。如果你不使用Guava，你可以自己编码:

/**
 * 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();
}

如果这个想法是将存储为双精度的整数打印出来，就像它们是整数一样，否则以最小的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);
}

生产:

232
0.18
1237875192
4.58
0
1.2345

并且不依赖于字符串操作。

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);
    }
}

这里有两种方法来实现它。首先，更短(可能更好)的方式:

public static String formatFloatToString(final float f)
{
  final int i = (int)f;
  if(f == i)
    return Integer.toString(i);
  return Float.toString(f);
}

这里有一个更长的，可能更糟糕的方法:

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;
}

这里有一个实际有效的答案(这里不同答案的组合)

public static String removeTrailingZeros(double f)
{
    if(f == (int)f) {
        return String.format("%d", (int)f);
    }
    return String.format("%f", f).replaceAll("0*$", "");
}

在我的机器上，下面的函数大约比JasonD的答案提供的函数快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:

如果你想摆脱尾随零和区域问题，那么你应该使用:

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

解释:

为什么其他答案不适合我:

Double.toString() or System.out.println or FloatingDecimal.toJavaFormatString uses scientific notations if double is less than 10^-3 or greater than or equal to 10^7 double myValue = 0.00000021d; String.format("%s", myvalue); //output: 2.1E-7 by using %f, the default decimal precision is 6, otherwise you can hardcode it, but it results in extra zeros added if you have fewer decimals. Example: double myValue = 0.00000021d; String.format("%.12f", myvalue); // Output: 0.000000210000 by using setMaximumFractionDigits(0); or %.0f you remove any decimal precision, which is fine for integers/longs but not for double 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 by using DecimalFormat, you are local dependent. In the French locale, the decimal separator is a comma, not a point: double myValue = 0.00000021d; DecimalFormat df = new DecimalFormat("0"); df.setMaximumFractionDigits(340); System.out.println(df.format(myvalue)); // Output: 0,00000021 Using the ENGLISH locale makes sure you get a point for decimal separator, wherever your program will run.

为什么使用340然后setMaximumFractionDigits?

两个原因:

setMaximumFractionDigits接受一个整数，但是它的实现有DecimalFormat允许的最大数字。DOUBLE_FRACTION_DIGITS等于340 翻倍。MIN_VALUE = 4.9E-324，因此使用340位数字，您肯定不会四舍五入的双精度和损失精度

Use:

if (d % 1.0 != 0)
    return String.format("%s", d);
else
    return String.format("%.0f", d);

这应该与Double支持的极值一起工作。它的收益率:

0.12
12
12.144252
0

请注意字符串。Format (Format, args…)依赖于语言环境，因为它使用用户的默认语言环境进行格式化，也就是说，可能在其中使用逗号甚至空格，如123 456,789或123,456.789，这可能不是您所期望的。

你可能更喜欢使用String.format((Locale)null, format, args…)

例如,

    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));

打印

123456,789000
123456,789000
123456.789000

这就是String的内容。Format (Format, args…)

EDIT好的，既然已经讨论了有关手续的问题:

    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;
}

你说你选择用双类型存储你的数字。我认为这可能是问题的根源，因为它迫使您将整数存储为双精度(因此丢失了关于值性质的初始信息)。将数字存储在Number类(Double和Integer的超类)的实例中，并依赖多态性来确定每个数字的正确格式如何?

我知道重构整个代码可能是不可接受的，但它可以在不需要额外的代码/强制转换/解析的情况下产生所需的输出。

例子:

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);
        }
    }

}

将产生以下输出:

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);
}

更多信息:https://docs.oracle.com/javase/tutorial/java/data/numberformat.html

我的观点是:

if(n % 1 == 0) {
    return String.format(Locale.US, "%.0f", n));
} else {
    return String.format(Locale.US, "%.1f", n));
}

下面这个可以很好地完成工作:

    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

0表示最小位数 渲染#数字

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);
}

我必须使用这个，因为d == (long)d在SonarQube报告中给了我违例。

使用DecimalFormat和setMinimumFractionDigits(0)。

这是我想到的:

  private static String format(final double dbl) {
    return dbl % 1 != 0 ? String.valueOf(dbl) : String.valueOf((int) dbl);
  }

它是一个简单的一行程序，仅在确实需要时才强制转换为int类型。

用分组、四舍五入和没有不必要的零(双位数)格式化价格。

规则:

末尾没有零(2.0000 = 2;1.0100000 = 1.01) 一个点后最多两位数(2.010 = 2.01;0.20 = 0.2) 一个点后的第二位数字(1.994 = 1.99;1.995 = 2;1.006 = 1.01;0.0006 -> 0 返回0 (null/-0 = 0) 增加$ (= $56/-$56) 分组(101101.02 = $101,101.02)

更多的例子:

-99.985 = -$99.99 10 = $10 10.00 = $10 20.01000089 = $20.01

它是用Kotlin编写的，作为Double的一个有趣的扩展(因为它在Android中使用)，但它可以很容易地转换为Java，因为使用了Java类。

/**
 * 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)
    }
}

使用方法:

var yourDouble: Double? = -20.00
println(yourDouble.formatUserAsSum()) // will print -$20

yourDouble = null
println(yourDouble.formatUserAsSum()) // will print $0

关于DecimalFormat: https://docs.oracle.com/javase/6/docs/api/java/text/DecimalFormat.html

对于Kotlin，你可以使用这样的扩展:

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));

以下是一些测试的结果:

4.30     => 4.3
4.39     => 4.39  // Choose format.setRoundingMode(RoundingMode.UP) to get 4.4
4.000000 => 4
4        => 4

这是另一个答案，它有一个选项，只有当小数不为零时才附加小数。

   /**
     * 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
    }

我在JSF应用程序中使用它来格式化数字，而不带后面的零。最初的内置格式化程序要求您指定小数位数的最大数量，如果您有太多小数位数，这在这里也很有用。

/**
 * 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;
}

考虑locale的简单解决方案:

double d = 123.45;
NumberFormat numberFormat = NumberFormat.getInstance(Locale.GERMANY);
System.out.println(numberFormat.format(d));

由于在德国使用逗号作为小数分隔符，因此上面将打印:

123,

使用给定的十进制长度…

public static String getLocaleFloatValueDecimalWithLength(Locale loc, float value, int length) {
        //make string from float value
        return String.format(loc, (value % 1 == 0 ? "%.0f" : "%."+length+"f"), value);
    }

0.0 -> 0% 1.0 -> 100% 0.1 -> 10% 0.11 -> 11% 0.01 -> 1% 0.111 -> 11.1% 0.001 -> 0.1% 0.1111 -> 11.11% 0.0001 -> 0.01%

添加".replace()"是因为我总是使用错误的分隔符

import java.text.NumberFormat

fun Double.formating(): String {
    val defaultFormat: NumberFormat = NumberFormat.getPercentInstance()
    defaultFormat.minimumFractionDigits = 0
    defaultFormat.maximumFractionDigits = 2

    return defaultFormat.format(this).replace(",", ".")
}