如何在Java中格式化数字？
如何在Java中格式化数字？
什么是“最佳实践”？
在格式化之前是否需要对数字进行舍入？
32.302342342342343=>32.30
.7323=>0.73
等等
从这个线程 ，有不同的方法来做到这一点：
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dynamic的方式，读取其他代码也很容易理解。
你和String.format()将是新的最好的朋友！
http://java.sun.com/j2se/1.5.0/docs/api/java/util/Formatter.html#syntax
String.format("%.2f", (double)value);
请注意，从NumberFormat（和大多数其他格式后裔）下降的类不同步。 创build格式对象并将它们存储在一个util类的静态variables中是一种常见（但危险）的做法。 在实践中，它会一直工作，直到它开始经历重大的负载。
整数，是的。 这是主要的例子来源 。
/* * Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * - Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * - Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * - Neither the name of Sun Microsystems nor the names of its * contributors may be used to endorse or promote products derived * from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ 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]); } } }
尝试这个：
String.format("%.2f", 32.302342342342343);
简单而高效。
使用DecimalFormat 。
标准库有两种方法。 一个是使用java.text.DecimalFormat。 基于java.util.Formatter的其他更神秘的方法（String.format，PrintStream.printf等）应该让C程序员满意（ish）。
正如Robert在他的回答中指出的那样：DecimalFormat既不同步也不保证线程安全（可能取决于您使用的JVM版本/供应商）。
而是使用Spring的Numberformatter ，这是线程安全的。
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formatDouble（）方法的double值是345.9372，那么结果如下：345.937同样，如果将值.7697传递给方法，则结果如下：.770
