Flash cards
Review the key moves
1/4
Core idea
What is the main idea behind Java String format() Method?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
1Quick choice
Which statement best captures the main point of this lesson?
2Fill blank
Complete the missing token from the example code.
___ myStr = "Hello %s! One kilobyte is %,d bytes.";3Order
Put the learning moves in the order that makes the concept easiest to apply.
List of conversions
Definition and Usage
Java String format() Method
❮ String Methods
Example
String myStr = "Hello %s! One kilobyte is %,d bytes.";
String result = String.format(myStr, "World", 1024);
System.out.println(result);Definition and Usage
The format() method returns a formatted string using a locale, format and additional arguments.
If a locale is not passed to this method then the locale given by Locale.getDefault() is used.
Data from the additional arguments is formatted and written into placeholders in the format string, which are marked by a % symbol. The way in which arguments are formatted depends on the sequence of characters that follows the % symbol.
Placeholders
The placeholders have the form %[arg$][flags][width][.precision]conversion . The components in [square brackets] are optional.
An explanation of each of the components:
- arg- Optional. A number followed by a sign which indicates which of the additional arguments to use, argument numbers start at 1. This can be replaced with a < which specifies that the argument from the previous placeholder should be used.
- flags - Optional. A sequence of any of the following characters: - - Makes the output left-justified by adding any padding spaces to the right instead of to the left. # - Shows an alternate representation of the formatted data depending on the conversion. + - Causes positive numbers to always be prefixed with "+". - (A space character) This prefixes a space to positive numbers, primarily so that the digits can be lined up with the digits of negative numbers. 0 - Pads numbers with zeroes on the left. , - Groups digits (for example by thousands) and puts separators between the groups. This is affected by the locale. ( - Encloses negative numbers in parentheses.
- width - Optional. A whole number specifying the minimum number of characters that the output should occupy. If necessary spaces are added to the left to reach this number, or to the right if the - flag is used.
- .precision Optional. A . followed by a whole number indicating how many decimal digits to show in the formatted data.
- conversion - Required. A character which indicates how an argument's data should be represented. If the character is uppercase the data will be formatted in uppercase where possible. The list of possible characters is shown in the table below.
- - - Makes the output left-justified by adding any padding spaces to the right instead of to the left.
- # - Shows an alternate representation of the formatted data depending on the conversion.
- + - Causes positive numbers to always be prefixed with "+".
- - (A space character) This prefixes a space to positive numbers, primarily so that the digits can be lined up with the digits of negative numbers.
- 0 - Pads numbers with zeroes on the left.
- , - Groups digits (for example by thousands) and puts separators between the groups. This is affected by the locale.
- ( - Encloses negative numbers in parentheses.
List of conversions
| Character | Conversion | Description |
|---|---|---|
| % | Percent | Displays a literal "%" character in the output. |
| n | Line break | Displays a line break in the output. |
| b or B | Boolean | Displays the boolean value of an argument as "true" or "false". If "B" is used then it displays "TRUE" or "FALSE" instead. |
| h or H | Hash code in hexadecimal | Displays the hash code of the argument in hexadecimal by using its hashCode() value. If H is used, the letters A to F are shown in uppercase. Note: This does not format a number as a hexadecimal integer. For hexadecimal integer formatting, use x or X . |
| s or S | String | Displays the default string representation of the argument. If "S" is used then the string will be converted to uppercase where possible. |
| c or C | Unicode character | Displays a unicode character representation of the argument. For whole numbers, this is the unicode character that corresponds to the number. If "C" is used then the character will be converted to uppercase where possible. |
| d | Decimal integer | Represents a whole number as a decimal integer. |
| o | Octal integer | Represents a whole number as an octal integer. The "#" flag will prefix the number with "0". |
| x or X | Hexadecimal integer | Represents a whole number as a hexadecimal integer. The "#" flag will prefix the number with "0x". If "X" is used then digits A to F and the letter X are shown in uppercase. |
| e or E | Scientific notation | Represents a floating point number in scientific notation. If "E" is used then the letter "E" of the representation will be uppercase. The "#" flag will force a decimal point even if there are no decimal digits. |
| f | Floating point number | Represents a floating point number. The "#" flag will force a decimal point even if there are no decimal digits. |
| g or G | General number | Displays the shortest representation between f and e or E for a floating point number. |
| a or A | Hexadecimal floating point number | Display a floating point number's internal representation with hexadecimal digits. |
| t or T | Time or date | Displays a formatted date or time. The t or T must be followed by one more character indicating how the date or time should be formatted. If "T" is used then text parts of a date or time such as "JANUARY" will be uppercase. The following characters can be used for date and time formatting: H - 24-hour format of an hour (00 to 23) I - 12-hour format of an hour (01 to 12) k - 24-hour format of an hour (0 to 23) l (lowercase 'L') - 12-hour format of an hour (1 to 12) M - Minutes with leading zeros (00 to 59) S - Seconds with leading zeros (00 to 59) (The value 60 may occur for leap seconds) L - Milliseconds with leading zeroes (000 to 999) N - Nanoseconds with leading zeroes (000000000 to 999999999) p - "am", "pm", "AM" or "PM" to indicate morning or afternoon z - Difference to Greenwich time (Example: -0800) Z - Timezone abbreviations (Examples: EST, MDT) s - The seconds since the Unix Epoch (January 1 1970 00:00:00 GMT) Q - The milliseconds since the Unix Epoch (January 1 1970 00:00:00 GMT) B - A full textual representation of a month (January through December) b or h - A short textual representation of a month (three letters) A - A full textual representation of a day (Example: Monday) a - A short textual representation of a day (Example: Mon) C - The first two digits of the year (For 1970, "19" would be shown) Y - A four digit representation of a year y - A two digit representation of a year j - The day of the year with leading zeroes (001 to 366) m - A numeric representation of a month (01 to 12) d - The day of the month (01 to 31) e - The day of the month without leading zeros (1 to 31) R - The time in 24-hour format (Example: 21:30) T - The time in 24-hour format with seconds (Example: 21:30:02) r - The time in 12-hour format with seconds (Example: 09:30:02 PM) ("AM" and "PM" are always uppercase) D - Date representation as month/day/year (Example: 12/17/23) F - Date representation as year-month-day (Example: 2023-12-17) c - Full date and time (Example: Thu Mar 28 10:51:00 EDT 2024) |
- H - 24-hour format of an hour (00 to 23)
- I - 12-hour format of an hour (01 to 12)
- k - 24-hour format of an hour (0 to 23)
- l (lowercase 'L') - 12-hour format of an hour (1 to 12)
- M - Minutes with leading zeros (00 to 59)
- S - Seconds with leading zeros (00 to 59) (The value 60 may occur for leap seconds)
- L - Milliseconds with leading zeroes (000 to 999)
- N - Nanoseconds with leading zeroes (000000000 to 999999999)
- p - "am", "pm", "AM" or "PM" to indicate morning or afternoon
- z - Difference to Greenwich time (Example: -0800)
- Z - Timezone abbreviations (Examples: EST, MDT)
- s - The seconds since the Unix Epoch (January 1 1970 00:00:00 GMT)
- Q - The milliseconds since the Unix Epoch (January 1 1970 00:00:00 GMT)
- B - A full textual representation of a month (January through December)
- b or h - A short textual representation of a month (three letters)
- A - A full textual representation of a day (Example: Monday)
- a - A short textual representation of a day (Example: Mon)
- C - The first two digits of the year (For 1970, "19" would be shown)
- Y - A four digit representation of a year
- y - A two digit representation of a year
- j - The day of the year with leading zeroes (001 to 366)
- m - A numeric representation of a month (01 to 12)
- d - The day of the month (01 to 31)
- e - The day of the month without leading zeros (1 to 31)
- R - The time in 24-hour format (Example: 21:30)
- T - The time in 24-hour format with seconds (Example: 21:30:02)
- r - The time in 12-hour format with seconds (Example: 09:30:02 PM) ("AM" and "PM" are always uppercase)
- D - Date representation as month/day/year (Example: 12/17/23)
- F - Date representation as year-month-day (Example: 2023-12-17)
- c - Full date and time (Example: Thu Mar 28 10:51:00 EDT 2024)
One of the following
public static String format(Locale
locale , String
format , Object...
args )public static String format(String
format , Object...
args )Parameter Values
| Parameter | Description |
|---|---|
| locale | Optional. A locale used to determine some of the formatting, such as which characters are used for decimal points and grouping separators. |
| format | Required. A string to be returned which can have placeholders for the additional arguments indicating how to format them. |
| args | Optional. Any number of additional arguments to the method, their values can be formatted and displayed in the returned string. |
Technical Details
| Returns: | A String value formatted using the specified locale, format and arguments. |
|---|---|
| Throws: | IllegalFormatException - if the format string contains an invalid placeholder or a placeholder isn't compatible with the data type of the argument. |
| Java version: | 1.5 |