java.util.Formatter is an interpreter for getting C language printf-style formatted strings. In Java, we usually use following methods to format console output which internally use Formatter class:
System.out.printf(String format, Object... args) System.out.printf(Locale l, String format, Object... args) |
| We can also use following methods of java.lang.String to get formatted strings: |
String format(String format, Object... args) String format(Locale l, String format, Object... args) |
The 'format' parameter in above methods, usually consists of one or multiple formatting specifier. A formatting specifier starts with %, which is a way to specify various formatting attributes to get the desired results.
In following examples we will quickly go through different formatting options available.
n - line terminator System.out.printf("abc%n456%n");
abc
456
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s or S - a String System.out.printf("%s%n", "this is my string");
System.out.printf("%S%n", "this is my string");
System.out.printf("%s%n", null);
System.out.printf("%s%n", 100);
System.out.printf("%s%n", new Object());
System.out.printf("'This is the example of %s.....'%n", "string");
this is my string
THIS IS MY STRING
null
100
java.lang.Object@247507be
'This is the example of string.....'
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b or B - true/false It will convert null/false to false , everything else to true
System.out.printf("%b%n", null);
System.out.printf("%b%n", false);
System.out.printf("%B%n", false);
false
false
FALSE
System.out.printf("%b%n", true);
System.out.printf("%b%n", "true");
System.out.printf("%b%n", "false");
System.out.printf("%b%n", "test");
System.out.printf("%b%n", 1);
System.out.printf("%b%n", 'c');
System.out.printf("%b%n", new Object());
true
true
true
true
true
true
true
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c or C - a char System.out.printf("%c%n", 'a');
System.out.printf("%C%n", 'a');
System.out.printf("%c%n", 100);
System.out.printf("%c%n", null);
a
A
d
null
For invalid char: System.out.printf("%c%n", "aString");
java.util.IllegalFormatConversionException: c != java.lang.String
at java.base/java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:4331)
at java.base/java.util.Formatter$FormatSpecifier.printCharacter(Formatter.java:2922)
at java.base/java.util.Formatter$FormatSpecifier.print(Formatter.java:2810)
......
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Formatting with padding
For left padding, an integer is used between % and the conversion specifier:
System.out.printf("Result: %20s%n", "example");
Result: example
For right padding additional - is used. System.out.printf("Result: %-20s%n", "example");
System.out.printf("%-20s result%n", "example");
Result: example
example result
Good for formatting multiple lines in columns: for (int i = 7; i < 300; i += 50) {
System.out.printf("[Item:%4s %-4s]%n", i, i * 10);
}
[Item: 7 70 ]
[Item: 57 570 ]
[Item: 107 1070]
[Item: 157 1570]
[Item: 207 2070]
[Item: 257 2570]
Precision This is used to limit chars.
Syntax: x.y where x= padding (width) and y= number of chars.
(For floating numbers y is used for decimal places - next sections.)
System.out.printf("%2.2s%n", "Hi there!");
System.out.printf("[%6.4s]%n", "What's up?");
System.out.printf("[%-6.4s]%n", "What's up?");
Hi
[ What]
[What ]
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d - byte/short/int/long/BigInteger formatting System.out.printf("%d%n", 2);
System.out.printf("%d%n", (byte) 2);
System.out.printf("%d%n", 2L);
System.out.printf("%d%n", BigInteger.valueOf(2L));
2
2
2
2
Invalid input (strings and other objects are also invalid): System.out.printf("%d%n", '2');
java.util.IllegalFormatConversionException: d != java.lang.Character
at java.base/java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:4331)
at java.base/java.util.Formatter$FormatSpecifier.printInteger(Formatter.java:2846)
at java.base/java.util.Formatter$FormatSpecifier.print(Formatter.java:2800)
......
Padding with zeros 0 is used just after % and then an int for padding
(as we saw in 'Formatting with padding' above).
System.out.printf("%04d", 2);
0002
Right zero padding is not possible. Using '%0-4d' or '%-04d'
will throw exception:
System.out.printf("%0-4d", 2);
java.util.IllegalFormatFlagsException: Flags = '-0'
at java.base/java.util.Formatter$FormatSpecifier.checkNumeric(Formatter.java:3084)
at java.base/java.util.Formatter$FormatSpecifier.checkInteger(Formatter.java:3039)
at java.base/java.util.Formatter$FormatSpecifier.(Formatter.java:2782)
......
Comma formatted numbers A comma is used between % and d
System.out.printf("%,d", 1000000);
1,000,000
For different locale System.out.printf(Locale.GERMAN, "%,d", 1000000);
1.000.000
Always include + sign for (int i = 1; i < 4; i++) {
System.out.printf("%+d%n", i);
}
+1
+2
+3
Always include parentheses for negative numbers for (int i = 1; i < 4; i++) {
System.out.printf("%(d%n", -i);
}
(1)
(2)
(3)
Always include leading space for positive numbers Only one space is allowed:
for (int i = 1; i < 4; i++) {
System.out.printf("[% d]%n", i);
}
[ 1]
[ 2]
[ 3]
Precision cannot be applied to integers System.out.printf("%6.4d", 123456);
java.util.IllegalFormatPrecisionException: 4
at java.base/java.util.Formatter$FormatSpecifier.checkInteger(Formatter.java:3041)
at java.base/java.util.Formatter$FormatSpecifier.(Formatter.java:2782)
at java.base/java.util.Formatter.parse(Formatter.java:2621)
......
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f - float/double formatting
System.out.printf("%f%n", 1.33f);
System.out.printf("%f%n", 1.33d);
System.out.printf("%f%n", Double.valueOf(1.33d));
System.out.printf("%f%n", BigDecimal.valueOf(1.33d));
1.330000
1.330000
1.330000
1.330000
Applying precisions: Syntax: x.y, where x is width (padding) and y is decimal places. Sometimes value of x is
ignored, if it's smaller than the necessary chars (including the decimal) to display.
Remember x is not to limit width but to add padding (spaces); y is to decrease/increase
decimal places.
System.out.printf("[%4.2f]%n", 12.34567);
System.out.printf("[%5.2f]%n", 12.34567);
System.out.printf("[%6.2f]%n", 12.34567);
System.out.printf("[%7.2f]%n", 12.34567);
System.out.printf("[%-7.2f]%n", 12.34567);
System.out.printf("[%7.4f]%n", 12.3);
System.out.printf("[%8.4f]%n", 12.3);
[12.35]
[12.35]
[ 12.35]
[ 12.35]
[12.35 ]
[12.3000]
[ 12.3000]
Always display decimal with # flag The integer portion of the result always ends with a
decimal point ('.'), even if the fractional portion is zero.
System.out.printf("[%#1.0f]%n", 1234d);
System.out.printf("[%1.0f]%n", 1234d);
[1234.]
[1234]
e or E - Scientific notation Syntax: x.ye => y=precision and x=total width (padding)
System.out.printf("%1.2e%n", 123.45);
System.out.printf("[%10.2e]%n", 123.45);
System.out.printf("[%-10.1e]%n", 123.45);
System.out.printf("%5.2E%n", 123.45);
1.23e+02
[ 1.23e+02]
[1.2e+02 ]
1.23E+02
g or G - Scientific notation
It depends on precision and rounding.
System.out.printf("%1.2g%n", 123.45);
System.out.printf("[%10.2g]%n", 123.45);
System.out.printf("[%-10.1g]%n", 123.45);
System.out.printf("[%-10.1G]%n", 123.45);
1.2e+02
[ 1.2e+02]
[1e+02 ]
[1E+02 ]
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Index based references A variable reference can be used as X$ just after %, where X is the index.
Following example is without referencing an index:
String test = "myString";
System.out.printf("%1.2s - %1.4s", test, test);
my - mySt
Using the reference: String test2 = "myString";
System.out.printf("%1$1.2s - %1$1.4s", test2);
my - mySt
Using multiple references: System.out.printf("%2$s | %3$1.4f | %1$,d", 1333, "hello", 5.4444);
hello | 5.4444 | 1,333
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System.out.printf("Hours: %tH%n", new Date());
System.out.printf("Mins: %tM%n", new Date());
System.out.printf("Secs: %tS%n", new Date());
Hours: 22
Mins: 09
Secs: 08
Date date = new Date();
System.out.printf("%tH:%tM:%tS%n", date, date, date);
//using index references
System.out.printf("%1$tH:%1$tM:%1$tS%n", date);
22:09:08
22:09:08
T can be used for %tH:%tM:%tS% format (last example): System.out.printf("%tT", new Date());
22:09:08
Time in am/pm format
I - for 12 hr clock
p - for am or pm
System.out.printf("%1$tI:%1$tM %1$tp", new Date());
10:09 pm
Time in milli/nanoseconds L - milliseconds
N - nanoseconds
System.out.printf("%1$tT %1$tL %1$tN", new Date());
22:09:08 357 357000000
TimeZone info z - timezone offset
Z - timezone id
System.out.printf("%1$tT %1$tz%n", new Date());
System.out.printf("%1$tT %1$tZ%n", new Date());
22:09:08 -0600
22:09:08 CST
Time since epoch s - epoch seconds
Q - epoch millis
System.out.printf("epoch sec: %1$ts%n", new Date());
System.out.printf("epoch millis: %1$tQ%n", new Date());
epoch sec: 1512014948
epoch millis: 1512014948440
Month B - full month name
b - abbreviated month name
m - year of month number 01 - 12
Date dt = Date.from(ZonedDateTime.of(LocalDate.of(2017, 2, 1).atStartOfDay(),
ZoneId.systemDefault()).toInstant());
System.out.printf("%tB%n", dt);
System.out.printf("%tb%n", dt);
System.out.printf("%tm%n", dt);
February
Feb
02
Day A - full name
a - abbreviated
d - day of month, 01 - 31
System.out.printf("%tA%n", new Date());
System.out.printf("%ta%n", new Date());
System.out.printf("%td%n", new Date());
Wednesday
Wed
29
Year Y - four digit year
y - two digit year
System.out.printf("%tY%n", new Date());
System.out.printf("%ty%n", new Date());
2017
17
Common formats shortcuts R - %tH:%tM
T - %tH:%tM:%tS
r - %tI:%tM:%tS %Tp
D - %tm/%td/%ty
F - %tY-%tm-%td
c - %ta %tb %td %tT %tZ %tY, e.g. Sun Jul 20 16:17:00 EDT 1969.
System.out.printf("%tR%n", new Date());
System.out.printf("%tT%n", new Date());
System.out.printf("%tr%n", new Date());
System.out.printf("%tD%n", new Date());
System.out.printf("%tF%n", new Date());
System.out.printf("%tc%n", new Date());
22:09
22:09:08
10:09:08 PM
11/29/17
2017-11-29
Wed Nov 29 22:09:08 CST 2017
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