Java IO.pdf - Nguyen Dang Binh

For example:
Java I/O
NumberFormat myFormat = NumberFormat.getNumberInstance();
NumberFormat canadaFormat = NumberFormat.getNumberInstance(Locale.CANADA);
16.3.1 Formatting Numbers
Once you've got a NumberFormat object, you can convert integers and floating point numbers
into formatted strings using one of NumberFormat's five overloaded format methods:
public final String format(long number)
public final String format(double number)
public abstract StringBuffer format(long number, StringBuffer toAppendTo,
FieldPosition pos)
public abstract StringBuffer format(double number, StringBuffer toAppendTo,
FieldPosition pos)
public final StringBuffer format(Object number, StringBuffer toAppendTo,
FieldPosition pos)
These methods all read the number and return a string or a modified string buffer based on
that number using the number format's default formatting rules. These rules generally specify:
• Maximum and minimum integer width
• Maximum and minimum fraction width (precision, number of decimal places)
• Whether or not digits are grouped (e.g., 2,109,356 versus 2109356)
For any given number format, these rules can be quite complex. For instance, they may or
may not take into account different digit sets, exponential or scientific notation, Roman
numerals, or more. By creating new subclasses of NumberFormat, you can specify arbitrarily
complex rules for converting binary numbers into strings. Regardless of exactly how a
number format formats numbers, they are all manipulated the same way.
The last three format() methods append the string to the specified StringBuffer
toAppendTo. They then return that modified string buffer. They use a
java.text.FieldPosition object to provide information to the client programmer about
where the different parts of the number fall. This will be discussed later. The final format()
method is used to format instances of the numeric type wrapper classes; that is,
java.lang.Double, java.lang.Float, java.lang.Long, java.lang.Integer,
java.lang.Short, java.lang.Character, and java.lang.Byte. It merely determines the
type of the argument and passes either the double or long value of the argument to the
format() method. Passing any other kind of object to this method will cause an
IllegalArgumentException.
Example 16.1 is about the simplest use of NumberFormat imaginable. It uses the default
number format for the default locale to print multiples of . For comparison, both the
formatted and unformatted numbers are printed.
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