Java String Format Examples

 

参考资料地址： 

文章地址： https://dzone.com/articles/java-string-format-examples

jdk API地址： https://docs.oracle.com/javase/8/docs/api/java/util/Formatter.html

 

 

 

Have you tried to read and understand Java’s String format documentation? I have and found it nearly impenetrable. While it does include all the information, the organization leaves something to be desired.

This guide is an attempt to bring some clarity and ease the usage of string formatting in Java.

String Formatting

The most common way of formatting a string in java is using String.format(). If there were a “java sprintf” then this would be it.

 

 

 

 

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String output = String.format("%s = %d", "joe", 35);

 

 

 

For formatted console output, you can use printf() or the format() method of System.out and System.err PrintStreams.

 

 

 

 

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System.out.printf("My name is: %s%n", "joe");

 

 

 

Create a Formatter and link it to a StringBuilder. Output formatted using the format() method will be appended to the StringBuilder.

 

 

 

 

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StringBuilder sbuf = new StringBuilder();

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Formatter fmt = new Formatter(sbuf);

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fmt.format("PI = %f%n", Math.PI);

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System.out.print(sbuf.toString());

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// you can continue to append data to sbuf here.

 

 

Format Specifiers

Here is a quick reference to all the conversion specifiers supported:

SPECIFIER	APPLIES TO	OUTPUT
%a	floating point (except BigDecimal)	Hex output of floating point number
%b	Any type	“true” if non-null, “false” if null
%c	character	Unicode character
%d	integer (incl. byte, short, int, long, bigint)	Decimal Integer
%e	floating point	decimal number in scientific notation
%f	floating point	decimal number
%g	floating point	decimal number, possibly in scientific notation depending on the precision and value.
%h	any type	Hex String of value from hashCode() method.
%n	none	Platform-specific line separator.
%o	integer (incl. byte, short, int, long, bigint)	Octal number
%s	any type	String value
%t	Date/Time (incl. long, Calendar, Date and TemporalAccessor)	%t is the prefix for Date/Time conversions. More formatting flags are needed after this. See Date/Time conversion below.
%x	integer (incl. byte, short, int, long, bigint)	Hex string.

Date and Time Formatting

Note: Using the formatting characters with “%T” instead of “%t” in the table below makes the output uppercase.

FLAG	NOTES
%tA	Full name of the day of the week, e.g. “Sunday“, “Monday“
%ta	Abbreviated name of the week day e.g. “Sun“, “Mon“, etc.
%tB	Full name of the month e.g. “January“, “February“, etc.
%tb	Abbreviated month name e.g. “Jan“, “Feb“, etc.
%tC	Century part of year formatted with two digits e.g. “00” through “99”.
%tc	Date and time formatted with “%ta %tb %td %tT %tZ %tY” e.g. “Fri Feb 17 07:45:42 PST 2017“
%tD	Date formatted as “%tm/%td/%ty“
%td	Day of the month formatted with two digits. e.g. “01” to “31“.
%te	Day of the month formatted without a leading 0 e.g. “1” to “31”.
%tF	ISO 8601 formatted date with “%tY-%tm-%td“.
%tH	Hour of the day for the 24-hour clock e.g. “00” to “23“.
%th	Same as %tb.
%tI	Hour of the day for the 12-hour clock e.g. “01” – “12“.
%tj	Day of the year formatted with leading 0s e.g. “001” to “366“.
%tk	Hour of the day for the 24 hour clock without a leading 0 e.g. “0” to “23“.
%tl	Hour of the day for the 12-hour click without a leading 0 e.g. “1” to “12“.
%tM	Minute within the hour formatted a leading 0 e.g. “00” to “59“.
%tm	Month formatted with a leading 0 e.g. “01” to “12“.
%tN	Nanosecond formatted with 9 digits and leading 0s e.g. “000000000” to “999999999”.
%tp	Locale specific “am” or “pm” marker.
%tQ	Milliseconds since epoch Jan 1 , 1970 00:00:00 UTC.
%tR	Time formatted as 24-hours e.g. “%tH:%tM“.
%tr	Time formatted as 12-hours e.g. “%tI:%tM:%tS %Tp“.
%tS	Seconds within the minute formatted with 2 digits e.g. “00” to “60”. “60” is required to support leap seconds.
%ts	Seconds since the epoch Jan 1, 1970 00:00:00 UTC.
%tT	Time formatted as 24-hours e.g. “%tH:%tM:%tS“.
%tY	Year formatted with 4 digits e.g. “0000” to “9999“.
%ty	Year formatted with 2 digits e.g. “00” to “99“.
%tZ	Time zone abbreviation. e.g. “UTC“, “PST“, etc.
%tz	Time Zone Offset from GMT e.g. “ -0800 “.

Argument Index

An argument index is specified as a number ending with a “$” after the “%” and selects the specified argument in the argument list.

 

 

 

 

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String.format("%2$s", 32, "Hello"); // prints: "Hello"

 

 

Formatting an Integer

With the %d format specifier, you can use an argument of all integral types including byte, short, int, long and BigInteger.

Default formatting:

 

 

 

 

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String.format("%d", 93); // prints 93

 

 

 

Specifying a width:

 

 

 

 

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String.format("|%20d|", 93); // prints: |                  93| 

 

 

 

Left-justifying within the specified width:

 

 

 

 

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String.format("|%-20d|", 93); // prints: |93                  |

 

 

 

Pad with zeros:

 

 

 

 

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String.format("|%020d|", 93); // prints: |00000000000000000093|

 

 

 

Print positive numbers with a “+”:

(Negative numbers always have the “-” included):

 

 

 

 

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String.format("|%+20d|', 93); // prints: |                 +93|

 

 

 

A space before positive numbers.

A “-” is included for negative numbers as per normal.

 

 

 

 

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String.format("|% d|", 93); // prints: | 93| String.format("|% d|", -36); // prints: |-36|

 

 

 

Use locale-specific thousands separator:

For the US locale, it is “,”:

 

 

 

 

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String.format("|%,d|", 10000000); // prints: |10,000,000|

 

 

 

Enclose negative numbers within parentheses (“()”) and skip the "-":

 

 

 

 

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String.format("|%(d|", -36); // prints: |(36)|

 

 

 

Octal output:

 

 

 

 

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String.format("|%o|"), 93); // prints: 135

 

 

 

Hex output:

 

 

 

 

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String.format("|%x|", 93); // prints: 5d

 

 

 

Alternate representation for octal and hex output:

Prints octal numbers with a leading “0” and hex numbers with leading “0x“.

 

 

 

 

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String.format("|%#o|", 93);

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// prints: 0135

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​

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String.format("|%#x|", 93);

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// prints: 0x5d

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​

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String.format("|%#X|", 93);

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// prints: 0X5D

 

 

 

String and Character Conversion

Default formatting:

Prints the whole string.

 

 

 

 

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String.format("|%s|", "Hello World"); // prints: "Hello World"

 

 

 

Specify Field Length

 

 

 

 

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String.format("|%30s|", "Hello World"); // prints: | Hello World|

 

 

 

Left Justify Text

 

 

 

 

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String.format("|%-30s|", "Hello World"); // prints: |Hello World |

 

 

 

Specify Maximum Number of Characters

 

 

 

 

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String.format("|%.5s|", "Hello World"); // prints: |Hello|

 

 

 

Field Width and Maximum Number of Characters

 

 

 

 

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String.format("|%30.5s|", "Hello World"); | Hello|

 

 

 

Summary

This guide explained String formatting in Java. We covered the supported format specifiers. Both numeric and string formatting support a variety of flags for alternative formats. If you want more content on Java Strings, check out the Do's and Don'ts of Java Strings.