如何在Java中格式化数字?
什么是“最佳实践”?
在格式化之前,我是否需要对数字进行舍入?
32.302342342342343
=>32.30
.7323
=>0.73
等
答案 0 :(得分:116)
从this thread开始,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()似乎是最有活力的方式,在阅读其他代码时也很容易理解。
答案 1 :(得分:73)
你和String.format()
将成为新的好朋友!
http://java.sun.com/j2se/1.5.0/docs/api/java/util/Formatter.html#syntax
String.format("%.2f", (double)value);
答案 2 :(得分:14)
请注意,从NumberFormat(以及大多数其他Format后代)继承的类不会同步。创建格式对象并将它们存储在util类中的静态变量中是一种常见(但危险)的做法。在实践中,它几乎总是有效,直到它开始经历重大负载。
答案 3 :(得分:11)
回合数字,是的。这是main example source。
/*
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* 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,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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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]);
}
}
}
答案 4 :(得分:8)
试试这个:
String.format("%.2f", 32.302342342342343);
简单而有效。
答案 5 :(得分:5)
答案 6 :(得分:4)
标准库中有两种方法。一种是使用java.text.DecimalFormat。基于java.util.Formatter的其他更加神秘的方法(String.format,PrintStream.printf等)应该让C程序员高兴(ish)。
答案 7 :(得分:2)
正如罗伯特在他的回答中指出的那样:DecimalFormat既不是同步的,也不是API保证线程安全(它可能取决于你正在使用的JVM版本/供应商)。
使用Spring的Numberformatter代替,这是线程安全的。
答案 8 :(得分:1)
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,则以下将是 结果是: 345.937 同样,如果将值.7697传递给方法,则结果如下: 0.770