java.lang.IllegalArgumentException：模式中有多个小数分隔符

Question

I want to format a number using a pattern in Java. I am getting error if the pattern has more than one decimal point. Here is the code:

    DecimalFormatSymbols symbols = new DecimalFormatSymbols();
    symbols.setDecimalSeparator(',');
    
    DecimalFormat df = new DecimalFormat();
    df.setDecimalFormatSymbols(symbols);
    df.applyPattern("#.###.###.###,##");
    
    String formattedValue = df.format("123456789");

Answer 1

I was testing it and it seems like the apply pattern needs a "," as grouping separator despite the one selected with the DecimalFormatSymbols. You can customize the result setting the grouping separator in the DecimalFormatSymbols as well. This is the code I tested in a Unit Test

    DecimalFormatSymbols symbols = new DecimalFormatSymbols();
    symbols.setDecimalSeparator(',');
    symbols.setGroupingSeparator('.');

    DecimalFormat df = new DecimalFormat();
    df.setDecimalFormatSymbols(symbols);
    df.applyPattern("#,###,###,###.##");

    Assertions.assertEquals("123.456.789,25", df.format(123456789.25));

And use a number in the df.format argument

Answer 2

Add the DecimalFormatSymbols#setGroupingSeparator('.') method to your code, for example:

DecimalFormatSymbols symbols = new DecimalFormatSymbols();
symbols.setDecimalSeparator(',');
symbols.setGroupingSeparator('.');  // Add This.

but also utilize a format that is specific to your system's current locale, for example:

df.applyPattern("#,###.##");

Notice that you really don't need to go as deep as you do with the format pattern. What is shown above will suffice. Numerical groups always contain 3 digits, you just need to specify that you want a separator character there

Also, use a number value rather than a numerical string, for example:

int value = 123456789; // or 123_456_789
String formattedValue = df.format(value);

Altogether, this should work:

DecimalFormatSymbols symbols = new DecimalFormatSymbols();
symbols.setDecimalSeparator(',');
symbols.setGroupingSeparator('.');     // Added this...

DecimalFormat df = new DecimalFormat();
df.setDecimalFormatSymbols(symbols);
df.applyPattern("#,###.##");   // Note the format pattern used.
    
int value = 123456789;**strong text**         // Use a number variable.
String formattedValue = df.format(value);
System.out.println(formattedValue);

Output to console:

123.456.789

Some countries like Italy, Spain, and Norway for example use this number format and with this in mind you could do this:

DecimalFormatSymbols symbols = new DecimalFormatSymbols(java.util.Locale.ITALIAN);
DecimalFormat df = new DecimalFormat("#,###.##", symbols);
int value = 123456789; // or 123_456_789
String formattedValue = df.format(value);
System.out.println(formattedValue);

Output to console:

123.456.789

Notice the Locale added to the DecimalFormatSymbols constructor (Locale.ITALIAN). Also notice the actual format. Use the format for your System's specific locale. Also notice that a int variable type containing a literal number is used instead of a numerical string.

Try it with a double type (floating point) value:

DecimalFormatSymbols symbols = new DecimalFormatSymbols(java.util.Locale.ITALIAN);
DecimalFormat df = new DecimalFormat("#,###.##", symbols);
double value = 1234567.89d;
String formattedValue = df.format(value);
System.out.println(formattedValue);

Output to console:

1.234.567,89