How do I format a number in Java

Question

How do I format a number in Java  What are the  quot Best Practices quot   Will I need to round a number before I format it   32 302342342342343   gt  32 30  7323   gt  0 73  etc

User · Answer

Use DecimalFormat

User · Answer

From this thread  there are different ways to do this   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   The DecimalFormat   seems to be the most dynamic way to do it  and it is also very easy to understand when reading others code

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public static void formatDouble double myDouble    NumberFormat numberFormatter   new DecimalFormat     000     String result   numberFormatter format myDouble    System out println result       For instance  if the double value passed into the formatDouble   method is 345 9372  the following will  be the result  345 937 Similarly  if the value  7697 is passed to the method  the following will be the result   770

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Round numbers  yes  This is the main example source            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  lt  locales length  i                  localizedFormat                123456 789  locales i

User · Answer

Be aware that classes that descend from NumberFormat  and most other Format descendants  are not synchronized  It is a common  but dangerous  practice to create format objects and store them in static variables in a util class  In practice  it will pretty much always work until it starts experiencing significant load

User · Answer

Try this   String format    2f   32 302342342342343     Simple and efficient

User · Answer

You and String format   will be new best friends   https   docs oracle com javase 1 5 0 docs api java util Formatter html syntax   String format    2f    double value

User · Answer

There are two approaches in the standard library  One is to use java text DecimalFormat  The other more cryptic methods  String format  PrintStream printf  etc  based around java util Formatter should keep C programmers happy ish

User · Answer

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     Use Spring s Numberformatter instead  which is thread safe

[java] How do I format a number in Java?

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