Formatters and Java Print Streams

The Formatter class and the printf() method inPrintStreamthat depends on it support several dozen format specifiers. In addition to integer and floating-point numbers,Formatter offers a wide range of date and time formats. It also has a few general formatters that can display absolutely any object or primitive data type.

All format specifiers begin with percent signs. The minimum format specifier is a percent sign followed by an alphabetic conversion code. This code identifies what the corresponding argument is to be formatted as. For instance,%fformats a number with a decimal point,%dformats it as a decimal (base-10) integer,%oformats it as an octal integer, and%xformats it as a hexadecimal integer. None of these specifiers changes what the number actually is; they’re just different ways of creating a string that represents the number.

To use a literal percent character in a format string, just double escape it. That is,%%is formatted as%in the output.

To get the platform default line separator, use%n.(\nis always a linefeed regardless of platform.%nmay be a carriage return, a linefeed, or a carriage return linefeed pair, depending on the platform.)

Integer conversions

Integer conversions can be applied to all integral types (specifically, byte, short,int, andlong, as well as the type-wrapper classesByte,Short,Integer,Long, and also thejava.math.BigIntegerclass). These conversions are:

%d
   A regular base-10 integer, such as 987

%o
   A base-8 octal integer, such as 1733

%x
   A base-16 lowercase hexadecimal integer, such as
   3db

%X
   A base-16 uppercase hexadecimal integer, such as 
   3DB

Example 7-1 prints the number 1023 in all four formats.

Example 7-1.  Integer format specifiers

public class IntegerFormatExample {

  public static void main(String[] args) {
    int n = 1023;
    System.out.printf("Decimal:    %d\n", n);
    System.out.printf("Octal:      %o\n", n);
    System.out.printf("Lowercase hexadecimal:                       %x\n", n);
    System.out.printf("Uppercase hexadecimal:                       %X\n", n);
  }
}

Here’s the output:

  Decimal:               1023
  Octal:                 1777
  Lowercase hexadecimal: 3ff
  Uppercase hexadecimal: 3FF