Comment formater un nombre en Java ?

Question

Comment formater un nombre en Java ?
Quelles sont les "meilleures pratiques" ?

Devrai-je arrondir un nombre avant de le formater ?

32.302342342342343 => 32.30

.7323 => 0.73

etc.

Answer 1

De ce fil Il existe plusieurs façons de procéder :

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

El DecimalFormat() semble être la manière la plus dynamique de le faire, et elle est également très facile à comprendre en lisant le code des autres.

Answer 2

Vous et String.format() seront les nouveaux meilleurs amis !

https://docs.oracle.com/javase/1.5.0/docs/api/java/util/Formatter.html#syntax

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

Answer 3

Sachez que les classes qui descendent de NumberFormat (et la plupart des autres descendants de Format) ne sont pas synchronisées. C'est une pratique courante (mais dangereuse) de créer des objets format et de les stocker dans des variables statiques dans une classe util. En pratique, cela fonctionnera presque toujours jusqu'à ce qu'il commence à subir une charge importante.

Answer 4

Des chiffres ronds, oui. C'est le principal exemple source .

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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]);
        }
     }
 }

Answer 5

Utilisez Format décimal .