Java system out printf string

Java String Formatting

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

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. '

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);

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

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);

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) .

Formatting with padding

For left padding, an integer is used between % and the conversion specifier:

System.out.printf("Result: %20s%n", "example");

System.out.printf("Result: %-20s%n", "example"); 
System.out.printf("%-20s result%n", "example");

Result: example example result

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?");

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));

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).

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(Locale.GERMAN, "%,d", 1000000);

Always include + sign

for (int i = 1; i < 4; i++) System.out.printf("%+d%n", i); 
>

Always include parentheses for negative numbers

for (int i = 1; i < 4; i++) System.out.printf("%(d%n", -i); 
>

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); 
>

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) .

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);

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);

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);

String test2 = "myString"; 
System.out.printf("%1$1.2s - %1$1.4s", test2);

Using multiple references:

System.out.printf("%2$s | %3$1.4f | %1$,d", 1333, "hello", 5.4444);

t or T — Date time formatting

System.out.printf("Hours: %tH%n", new Date()); 
System.out.printf("Mins: %tM%n", new Date()); 
System.out.printf("Secs: %tS%n", new Date());

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);

System.out.printf("%tT", new Date());

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());

Time in milli/nanoseconds

L — milliseconds
N — nanoseconds

System.out.printf("%1$tT %1$tL %1$tN", new Date());

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());

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);

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());

Year

Y — four digit year
y — two digit year

System.out.printf("%tY%n", new Date()); 
System.out.printf("%ty%n", new Date());

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

Источник