How to escape a string to be passed into DecimalFormat

Question

May I know how I can escape a string to be passed into decimal format?

// currencySymbolPrefix can be any string.
NumberFormat numberFormat = new DecimalFormat(currencySymbolPrefix + "#,##0.00");

How can I escape currencySymbolPrefix, so that it may contains any characters including '#', and will not be interpreted as one of the pattern.

Please do not suggest

NumberFormat numberFormat = new DecimalFormat("#,##0.00");
final String output = currencySymbolPrefix + numberFormat.format(number);

as my vendor's method only accept single NumberFormat.

Answer 1

You can use apostrophes to quote:

String pattern = "'" + currencySymbolPrefix + "'#,##0.00";
NumberFormat numberFormat = new DecimalFormat(pattern);

If currencySymbolPrefix itself may contain apostrophes, you'd need to escape those by doubling them:

String pattern = "'" + currencySymbolPrefix.replace("'", "''") + "'#,##0.00";

Answer 2

On quoting special characters to treat them literally

The DecimalFormat allows you to quote special characters to treat them literally.

Many characters in a pattern are taken literally; they are matched during parsing and output unchanged during formatting. Special characters, on the other hand, stand for other characters, strings, or classes of characters. They must be quoted, unless noted otherwise, if they are to appear in the prefix or suffix as literals.

' can be used to quote special characters in a prefix or suffix, for example, "'#'#" formats 123 to "#123". To create a single quote itself, use two in a row: "# o''clock".

Thus, you can write a general purpose string escaper for DecimalFormat like this:

// a general-purpose string escaper for DecimalFormat

public static String escapeDecimalFormat(String s) {
    return "'" + s.replace("'", "''") + "'";
}

Then you can use it in your case like this:

    String currencySymbolPrefix = "<'#'>";
    NumberFormat numberFormat = new DecimalFormat(
        escapeDecimalFormat(currencySymbolPrefix) + "#,##0.00"
    );  
    System.out.println(numberFormat.format(123456.789));
    // <'#'>123,456.79

---

On inserting currency symbols in DecimalFormat

It should be noted that for currency symbols, NumberFormat does in fact have the method setCurrency(Currency). DecimalFormat implements this method. If you are using one of the ISO 4217 currencies, you can use a java.util.Currency instance to setCurrency on a DecimalFormat. This will take care of the symbol mapping etc for you too.

¤ (\u00A4) is the currency sign, replaced by currency symbol. If doubled, replaced by international currency symbol. If present in a pattern, the monetary decimal separator is used instead of the decimal separator.

Here's an example:

    NumberFormat numberFormat = new DecimalFormat("¤#,##0.00");
    numberFormat.setCurrency(Currency.getInstance("USD"));
    System.out.println(numberFormat.format(123456.789));
    // $123,456.79