如何用 Java 格式化数字？

从 这根线来看，有不同的方法可以做到这一点:

double r = 5.1234;
System.out.println(r); // r is 5.1234


int decimalPlaces = 2;
BigDecimal bd = new BigDecimal(r);


// setScale is immutable
bd = bd.setScale(decimalPlaces, BigDecimal.ROUND_HALF_UP);
r = bd.doubleValue();


System.out.println(r); // r is 5.12

f = (float) (Math.round(n*100.0f)/100.0f);

DecimalFormat df2 = new DecimalFormat( "#,###,###,##0.00" );
double dd = 100.2397;
double dd2dec = new Double(df2.format(dd)).doubleValue();


// The value of dd2dec will be 100.24

DecimalFormat()似乎是最动态的实现方式，而且在阅读其他代码时也非常容易理解。

你和 String.format()将成为新的最好的朋友！

Https://docs.oracle.com/javase/1.5.0/docs/api/java/util/formatter.html#syntax

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

使用 DecimalFormat。

整数，是的，这是 主要示例资料来源。

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import java.util.*;
import java.text.*;


public class DecimalFormatDemo {


static public void customFormat(String pattern, double value ) {
DecimalFormat myFormatter = new DecimalFormat(pattern);
String output = myFormatter.format(value);
System.out.println(value + "  " + pattern + "  " + output);
}


static public void localizedFormat(String pattern, double value,                                       Locale loc ) {
NumberFormat nf = NumberFormat.getNumberInstance(loc);
DecimalFormat df = (DecimalFormat)nf;
df.applyPattern(pattern);
String output = df.format(value);
System.out.println(pattern + "  " + output + "  " + loc.toString());
}


static public void main(String[] args) {


customFormat("###,###.###", 123456.789);
customFormat("###.##", 123456.789);
customFormat("000000.000", 123.78);
customFormat("$###,###.###", 12345.67);
customFormat("\u00a5###,###.###", 12345.67);


Locale currentLocale = new Locale("en", "US");


DecimalFormatSymbols unusualSymbols = new DecimalFormatSymbols(currentLocale);
unusualSymbols.setDecimalSeparator('|');
unusualSymbols.setGroupingSeparator('^');
String strange = "#,##0.###";
DecimalFormat weirdFormatter = new DecimalFormat(strange, unusualSymbols);
weirdFormatter.setGroupingSize(4);
String bizarre = weirdFormatter.format(12345.678);
System.out.println(bizarre);


Locale[] locales = {
new Locale("en", "US"),
new Locale("de", "DE"),
new Locale("fr", "FR")
};


for (int i = 0; i < locales.length; i++) {
localizedFormat("###,###.###", 123456.789, locales[i]);
}
}
}

标准库中有两种方法。一种是使用 java.text。DecimalFormat 十进制格式。其他基于 java.util 的更加神秘的方法(String.format、 PrintStream.printf 等)。格式化程序应该让 C 程序员高兴(差不多)。

请注意，从 NumberFormat (以及大多数其他 Format 的后代)派生的类是不同步的。创建格式化对象并将它们存储在 util 类的静态变量中是一种常见的(但是危险的)做法。在实践中，它几乎总是工作，直到它开始经历重大负载。

As Robert has pointed out in his answer: DecimalFormat is neither synchronized nor does the API guarantee thread safety (it might depend on the JVM version/vendor you are using).

改用 Spring 的 数字格式化程序，它是线程安全的。

Try this:

String.format("%.2f", 32.302342342342343);

简单高效。

public static void formatDouble(double myDouble){
NumberFormat numberFormatter = new DecimalFormat("##.000");
String result = numberFormatter.format(myDouble);
System.out.println(result);
}

例如，如果传递给 format Double ()方法的 double 值为345.9372，则以下代码将 结果是: 345.937 类似地，如果将.7697值传递给该方法，结果如下: 。770