Learning Java, 4th Edition

Formatting with the java.text Package

The java.text package includes, among other things, a set of classes designed for generating and parsing string representations of objects. In this section, we’ll talk about three classes: NumberFormat, ChoiceFormat, and MessageFormat. Chapter 11 describes the DateFormat class. As we said earlier, the classes of the java.text package overlap to a large degree with the capabilities of the Scanner and printf-style Formatter. Despite these new features, a number of areas in the parsing of currencies, dates, and times can only be handled with the java.text package.

The NumberFormat class can be used to format and parse currency, percentages, or plain old numbers. NumberFormat is an abstract class, but it has several useful factory methods that produce formatters for different types of numbers. For example, to format or parse currency strings, use getCurrencyInstance() :

    double salary = 1234.56;
    String here =     // $1,234.56
        NumberFormat.getCurrencyInstance().format(salary);
    String italy =    // L 1.234,56
        NumberFormat.getCurrencyInstance(Locale.ITALY).format(salary);

The first statement generates an American salary, with a dollar sign, a comma to separate thousands, and a period as a decimal point. The second statement presents the same string in Italian, with a lire sign, a period to separate thousands, and a comma as a decimal point. Remember that NumberFormat worries about format only; it doesn’t attempt to do currency conversion. We can go the other ...