java.lang.Object | |
↳ | java.util.Formatter |
Formats arguments according to a format string (like printf
in C).
It's relatively rare to use a Formatter
directly. A variety of classes offer convenience
methods for accessing formatter functionality.
Of these, format(String, Object...)
is generally the most useful.
PrintStream
and PrintWriter
both offer
format
and printf
methods.
Format strings consist of plain text interspersed with format specifiers, such
as "name: %s weight: %03dkg\n"
. Being a Java string, the usual Java string literal
backslash escapes are of course available.
Format specifiers (such as "%s"
or "%03d"
in the example) start with a
%
and describe how to format their corresponding argument. It includes an optional
argument index, optional flags, an optional width, an optional precision, and a mandatory
conversion type.
In the example, "%s"
has no flags, no width, and no precision, while
"%03d"
has the flag 0
, the width 3, and no precision.
Not all combinations of argument index, flags, width, precision, and conversion type are valid.
Argument index. Normally, each format specifier consumes the next argument to
format
.
For convenient localization, it's possible to reorder arguments so that they appear in a
different order in the output than the order in which they were supplied.
For example, "%4$s"
formats the fourth argument (4$
) as a string (s
).
It's also possible to reuse an argument with <
. For example,
format("%o %<d %<x", 64)
results in "100 64 40"
.
Flags. The available flags are:
Flags | |||
, |
Use grouping separators for large numbers. (Decimal only.) | format("%,d", 1024); |
1,234 |
+ |
Always show sign. (Decimal only.) | format("%+d, %+4d", 5, 5); |
+5, +5 |
|
A space indicates that non-negative numbers should have a leading space. (Decimal only.) | format("x% d% 5d", 4, 4); |
x 4 4 |
( |
Put parentheses around negative numbers. (Decimal only.) | format("%(d, %(d, %(6d", 12, -12, -12); |
12, (12), (12) |
- |
Left-justify. (Requires width.) | format("%-6dx", 5); format("%-3C, %3C", 'd', 0x65); |
5 x D , E |
0 |
Pad the number with leading zeros. (Requires width.) | format("%07d, %03d", 4, 5555); |
0000004, 5555 |
# |
Alternate form. (Octal and hex only.) | format("%o %#o", 010, 010); format("%x %#x", 0x12, 0x12); |
10 010 12 0x12 |
Width. The width is a decimal integer specifying the minimum number of characters to be used to represent the argument. If the result would otherwise be shorter than the width, padding will be added (the exact details of which depend on the flags). Note that you can't use width to truncate a field, only to make it wider: see precision for control over the maximum width.
Precision. The precision is a .
followed by a decimal integer, giving the minimum
number of digits for d
, o
, x
, or X
; the minimum number of digits
after the decimal point for a
, A
, e
, E
, f
, or F
;
the maximum number of significant digits for g
or G
; or the maximum number of
characters for s
or S
.
Conversion type. One or two characters describing how to interpret the argument. Most
conversions are a single character, but date/time conversions all start with t
and
have a single extra character describing the desired output.
Many conversion types have a corresponding uppercase variant that converts its result to uppercase using the rules of the relevant locale (either the default or the locale set for this formatter).
This table shows the available single-character (non-date/time) conversion types:
String conversions
All types are acceptable arguments. Values of type Formattable have their
formatTo method invoked; all other types use toString .
|
|||
s |
String. | format("%s %s", "hello", "Hello"); |
hello Hello |
S |
Uppercase string. | format("%S %S", "hello", "Hello"); |
HELLO HELLO |
Character conversions
Byte, Character, Short, and Integer (and primitives that box to those types) are all acceptable as character arguments. Any other type is an error. |
|||
c |
Character. | format("%c %c", 'd', 'E'); |
d E |
C |
Uppercase character. | format("%C %C", 'd', 'E'); |
D E |
Integer conversions
Byte, Short, Integer, Long, and BigInteger (and primitives that box to those types) are all acceptable as integer arguments. Any other type is an error. |
|||
d |
Decimal. | format("%d", 26); |
26 |
o |
Octal. | format("%o", 032); |
32 |
x , X |
Hexadecimal. | format("%x %X", 0x1a, 0x1a); |
1a 1A |
Floating-point conversions
Float, Double, and BigDecimal (and primitives that box to those types) are all acceptable as floating-point arguments. Any other type is an error. |
|||
f |
Decimal floating point. | format("%f", 123.456f); format("%.1f", 123.456f); format("%1.5f", 123.456f); format("%10f", 123.456f); format("%6.0f", 123.456f); |
123.456001 123.5 123.45600 123.456001 123 |
e , E |
Engineering/exponential floating point. | format("%e", 123.456f); format("%.1e", 123.456f); format("%1.5E", 123.456f); format("%10E", 123.456f); format("%6.0E", 123.456f); |
1.234560e+02 1.2e+02 1.23456E+02 1.234560E+02 1E+02 |
g , G |
Decimal or engineering, depending on the magnitude of the value. | format("%g %g", 0.123, 0.0000123); |
0.123000 1.23000e-05 |
a , A |
Hexadecimal floating point. | format("%a", 123.456f); |
0x1.edd2f2p6 |
Boolean conversion
Accepts Boolean values. null is considered false, and instances of all other
types are considered true.
|
|||
b , B |
Boolean. | format("%b %b", true, false); format("%B %B", true, false); format("%b", null); format("%b", "hello"); |
true false TRUE FALSE false true |
Hash code conversion
Invokes hashCode on its argument, which may be of any type.
|
|||
h , H |
Hexadecimal hash code. | format("%h", this); format("%H", this); format("%h", null); |
190d11 190D11 null |
Zero-argument conversions | |||
% |
A literal % character. | format("%d%%", 50); |
50% |
n |
Newline. (The value of lineSeparator() .) |
format("first%nsecond"); |
first\nsecond |
It's also possible to format dates and times with Formatter
, though you should
use SimpleDateFormat
(probably via the factory methods in
DateFormat
) instead.
The facilities offered by Formatter
are low-level and place the burden of localization
on the developer. Using getDateInstance()
,
getTimeInstance()
, and
getDateTimeInstance()
is preferable for dates and times that will be
presented to a human. Those methods will select the best format strings for the user's locale.
The best non-localized form is ISO 8601,
which you can get with "%tF"
(2010-01-22), "%tF %tR"
(2010-01-22 13:39),
"%tF %tT"
(2010-01-22 13:39:15), or "%tF %tT%z"
(2010-01-22 13:39:15-0800).
This table shows the date/time conversions, but you should use SimpleDateFormat
instead:
Date/time conversions
Calendar, Date, and Long (representing milliseconds past the epoch) are all acceptable as date/time arguments. Any other type is an error. The epoch is 1970-01-01 00:00:00 UTC. Use SimpleDateFormat instead.
|
|||
ta |
Localized weekday name (abbreviated). | format("%ta", cal, cal); |
Tue |
tA |
Localized weekday name (full). | format("%tA", cal, cal); |
Tuesday |
tb |
Localized month name (abbreviated). | format("%tb", cal); |
Apr |
tB |
Localized month name (full). | format("%tB", cal); |
April |
tc |
C library asctime(3)-like output. Do not use. | format("%tc", cal); |
Tue Apr 01 16:19:17 CEST 2008 |
tC |
2-digit century. | format("%tC", cal); |
20 |
td |
2-digit day of month (01-31). | format("%td", cal); |
01 |
tD |
Ambiguous US date format (MM/DD/YY). Do not use. | format("%tD", cal); |
04/01/08 |
te |
Day of month (1-31). | format("%te", cal); |
1 |
tF |
Full date in ISO 8601 format (YYYY-MM-DD). | format("%tF", cal); |
2008-04-01 |
th |
Synonym for %tb . |
||
tH |
2-digit 24-hour hour of day (00-23). | format("%tH", cal); |
16 |
tI |
2-digit 12-hour hour of day (01-12). | format("%tI", cal); |
04 |
tj |
3-digit day of year (001-366). | format("%tj", cal); |
092 |
tk |
24-hour hour of day (0-23). | format("%tk", cal); |
16 |
tl |
12-hour hour of day (1-12). | format("%tl", cal); |
4 |
tL |
Milliseconds. | format("%tL", cal); |
359 |
tm |
2-digit month of year (01-12). | format("%tm", cal); |
04 |
tM |
2-digit minute. | format("%tM", cal); |
08 |
tN |
Nanoseconds. | format("%tN", cal); |
359000000 |
tp |
a.m. or p.m. | format("%tp %Tp", cal, cal); |
pm PM |
tQ |
Milliseconds since the epoch. | format("%tQ", cal); |
1207059412656 |
tr |
Full 12-hour time (%tI:%tM:%tS %Tp ). |
format("%tr", cal); |
04:15:32 PM |
tR |
Short 24-hour time (%tH:%tM ). |
format("%tR", cal); |
16:15 |
ts |
Seconds since the epoch. | format("%ts", cal); |
1207059412 |
tS |
2-digit seconds (00-60). | format("%tS", cal); |
17 |
tT |
Full 24-hour time (%tH:%tM:%tS ). |
format("%tT", cal); |
16:15:32 |
ty |
2-digit year (00-99). | format("%ty", cal); |
08 |
tY |
4-digit year. | format("%tY", cal); |
2008 |
tz |
Time zone GMT offset. | format("%tz", cal); |
+0100 |
tZ |
Localized time zone abbreviation. | format("%tZ", cal); |
CEST |
As with the other conversions, date/time conversion has an uppercase format. Replacing
%t
with %T
will uppercase the field according to the rules of the formatter's
locale.
Number localization. Some conversions use localized decimal digits rather than the
usual ASCII digits. So formatting 123
with %d
will give 123 in English locales
but ١٢٣ in appropriate Arabic locales, for example. This number localization
occurs for the decimal integer conversion %d
, the floating point conversions %e
,
%f
, and %g
, and all date/time %t
or %T
conversions, but no other
conversions.
Thread safety. Formatter is not thread-safe.
Nested Classes | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Formatter.BigDecimalLayoutForm | The enumeration giving the available styles for formatting very large decimal numbers. |
Public Constructors | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Constructs a
Formatter . | |||||||||||
Constructs a
Formatter whose output will be written to the
specified Appendable . | |||||||||||
Constructs a
Formatter with the specified Locale . | |||||||||||
Constructs a
Formatter with the specified Locale
and whose output will be written to the
specified Appendable . | |||||||||||
Constructs a
Formatter whose output is written to the specified file. | |||||||||||
Constructs a
Formatter whose output is written to the specified file. | |||||||||||
Constructs a
Formatter with the given Locale and charset,
and whose output is written to the specified file. | |||||||||||
Constructs a
Formatter whose output is written to the specified File . | |||||||||||
Constructs a
Formatter with the given charset,
and whose output is written to the specified File . | |||||||||||
Constructs a
Formatter with the given Locale and charset,
and whose output is written to the specified File . | |||||||||||
Constructs a
Formatter whose output is written to the specified OutputStream . | |||||||||||
Constructs a
Formatter with the given charset,
and whose output is written to the specified OutputStream . | |||||||||||
Constructs a
Formatter with the given Locale and charset,
and whose output is written to the specified OutputStream . | |||||||||||
Constructs a
Formatter whose output is written to the specified PrintStream . |
Public Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Closes the
Formatter . | |||||||||||
Flushes the
Formatter . | |||||||||||
Writes a formatted string to the output destination of the
Formatter . | |||||||||||
Writes a formatted string to the output destination of the
Formatter . | |||||||||||
Returns the last
IOException thrown by the Formatter 's output
destination. | |||||||||||
Returns the
Locale of the Formatter . | |||||||||||
Returns the output destination of the
Formatter . | |||||||||||
Returns the content by calling the
toString() method of the output
destination. |
[Expand]
Inherited Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.lang.Object
| |||||||||||
From interface
java.io.Closeable
| |||||||||||
From interface
java.io.Flushable
| |||||||||||
From interface
java.lang.AutoCloseable
|
Constructs a Formatter
.
The output is written to a StringBuilder
which can be acquired by invoking
out()
and whose content can be obtained by calling toString
.
The Locale
used is the user's default locale.
See "Be wary of the default locale".
Constructs a Formatter
whose output will be written to the
specified Appendable
.
The Locale
used is the user's default locale.
See "Be wary of the default locale".
a | the output destination of the Formatter . If a is null ,
then a StringBuilder will be used.
|
---|
Constructs a Formatter
with the specified Locale
.
The output is written to a StringBuilder
which can be acquired by invoking
out()
and whose content can be obtained by calling toString
.
l | the Locale of the Formatter . If l is null ,
then no localization will be used.
|
---|
Constructs a Formatter
with the specified Locale
and whose output will be written to the
specified Appendable
.
a | the output destination of the Formatter . If a is null ,
then a StringBuilder will be used. |
---|---|
l | the Locale of the Formatter . If l is null ,
then no localization will be used.
|
Constructs a Formatter
whose output is written to the specified file.
The charset of the Formatter
is the default charset.
The Locale
used is the user's default locale.
See "Be wary of the default locale".
fileName | the filename of the file that is used as the output
destination for the Formatter . The file will be truncated to
zero size if the file exists, or else a new file will be
created. The output of the Formatter is buffered. |
---|
FileNotFoundException | if the filename does not denote a normal and writable file, or if a new file cannot be created, or if any error arises when opening or creating the file. |
---|
Constructs a Formatter
whose output is written to the specified file.
The Locale
used is the user's default locale.
See "Be wary of the default locale".
fileName | the filename of the file that is used as the output
destination for the Formatter . The file will be truncated to
zero size if the file exists, or else a new file will be
created. The output of the Formatter is buffered. |
---|---|
csn | the name of the charset for the Formatter . |
FileNotFoundException | if the filename does not denote a normal and writable file, or if a new file cannot be created, or if any error arises when opening or creating the file. |
---|---|
UnsupportedEncodingException | if the charset with the specified name is not supported. |
Constructs a Formatter
with the given Locale
and charset,
and whose output is written to the specified file.
fileName | the filename of the file that is used as the output
destination for the Formatter . The file will be truncated to
zero size if the file exists, or else a new file will be
created. The output of the Formatter is buffered. |
---|---|
csn | the name of the charset for the Formatter . |
l | the Locale of the Formatter . If l is null ,
then no localization will be used. |
FileNotFoundException | if the filename does not denote a normal and writable file, or if a new file cannot be created, or if any error arises when opening or creating the file. |
---|---|
UnsupportedEncodingException | if the charset with the specified name is not supported. |
Constructs a Formatter
whose output is written to the specified File
.
The charset of the Formatter
is the default charset.
The Locale
used is the user's default locale.
See "Be wary of the default locale".
file | the File that is used as the output destination for the
Formatter . The File will be truncated to zero size if the File
exists, or else a new File will be created. The output of the
Formatter is buffered. |
---|
FileNotFoundException | if the File is not a normal and writable File , or if a
new File cannot be created, or if any error rises when opening or
creating the File .
|
---|
Constructs a Formatter
with the given charset,
and whose output is written to the specified File
.
The Locale
used is the user's default locale.
See "Be wary of the default locale".
file | the File that is used as the output destination for the
Formatter . The File will be truncated to zero size if the File
exists, or else a new File will be created. The output of the
Formatter is buffered. |
---|---|
csn | the name of the charset for the Formatter . |
FileNotFoundException | if the File is not a normal and writable File , or if a
new File cannot be created, or if any error rises when opening or
creating the File . |
---|---|
UnsupportedEncodingException | if the charset with the specified name is not supported. |
Constructs a Formatter
with the given Locale
and charset,
and whose output is written to the specified File
.
file | the File that is used as the output destination for the
Formatter . The File will be truncated to zero size if the File
exists, or else a new File will be created. The output of the
Formatter is buffered. |
---|---|
csn | the name of the charset for the Formatter . |
l | the Locale of the Formatter . If l is null ,
then no localization will be used. |
FileNotFoundException | if the File is not a normal and writable File , or if a
new File cannot be created, or if any error rises when opening or
creating the File . |
---|---|
UnsupportedEncodingException | if the charset with the specified name is not supported. |
Constructs a Formatter
whose output is written to the specified OutputStream
.
The charset of the Formatter
is the default charset.
The Locale
used is the user's default locale.
See "Be wary of the default locale".
os | the stream to be used as the destination of the Formatter .
|
---|
Constructs a Formatter
with the given charset,
and whose output is written to the specified OutputStream
.
The Locale
used is the user's default locale.
See "Be wary of the default locale".
os | the stream to be used as the destination of the Formatter . |
---|---|
csn | the name of the charset for the Formatter . |
UnsupportedEncodingException | if the charset with the specified name is not supported. |
---|
Constructs a Formatter
with the given Locale
and charset,
and whose output is written to the specified OutputStream
.
os | the stream to be used as the destination of the Formatter . |
---|---|
csn | the name of the charset for the Formatter . |
l | the Locale of the Formatter . If l is null ,
then no localization will be used. |
UnsupportedEncodingException | if the charset with the specified name is not supported. |
---|
Constructs a Formatter
whose output is written to the specified PrintStream
.
The charset of the Formatter
is the default charset.
The Locale
used is the user's default locale.
See "Be wary of the default locale".
ps | the PrintStream used as destination of the Formatter . If
ps is null , then a NullPointerException will
be raised.
|
---|
Closes the Formatter
. If the output destination is Closeable
,
then the method close()
will be called on that destination.
If the Formatter
has been closed, then calling the this method will have no
effect.
Any method but the ioException()
that is called after the
Formatter
has been closed will raise a FormatterClosedException
.
Flushes the Formatter
. If the output destination is Flushable
,
then the method flush()
will be called on that destination.
FormatterClosedException | if the Formatter has been closed.
|
---|
Writes a formatted string to the output destination of the Formatter
.
format | a format string. |
---|---|
args | the arguments list used in the format() method. If there are
more arguments than those specified by the format string, then
the additional arguments are ignored. |
Formatter
.IllegalFormatException | if the format string is illegal or incompatible with the arguments, or if fewer arguments are sent than those required by the format string, or any other illegal situation. |
---|---|
FormatterClosedException | if the Formatter has been closed.
|
Writes a formatted string to the output destination of the Formatter
.
l | the Locale used in the method. If locale is
null , then no localization will be applied. This
parameter does not change this Formatter's default Locale
as specified during construction, and only applies for the
duration of this call. |
---|---|
format | a format string. |
args | the arguments list used in the format() method. If there are
more arguments than those specified by the format string, then
the additional arguments are ignored. |
Formatter
.IllegalFormatException | if the format string is illegal or incompatible with the arguments, or if fewer arguments are sent than those required by the format string, or any other illegal situation. |
---|---|
FormatterClosedException | if the Formatter has been closed.
|
Returns the last IOException
thrown by the Formatter
's output
destination. If the append()
method of the destination does not throw
IOException
s, the ioException()
method will always return null
.
IOException
thrown by the Formatter
's output
destination.
Returns the Locale
of the Formatter
.
Locale
for the Formatter
or null
for no Locale
.FormatterClosedException | if the Formatter has been closed.
|
---|
Returns the output destination of the Formatter
.
Formatter
.FormatterClosedException | if the Formatter has been closed.
|
---|
Returns the content by calling the toString()
method of the output
destination.
toString()
method of the output
destination.FormatterClosedException | if the Formatter has been closed.
|
---|