Formattable
Stay organized with collections
Save and categorize content based on your preferences.
The Formattable interface must be implemented by any class that
needs to perform custom formatting using the 's' conversion
specifier of Formatter. This interface allows basic
control for formatting arbitrary objects.
For example, the following class prints out different representations of a
stock's name depending on the flags and length constraints:
import java.nio.CharBuffer;
import java.util.Formatter;
import java.util.Formattable;
import java.util.Locale;
import static java.util.FormattableFlags.*;
...
public class StockName implements Formattable {
private String symbol, companyName, frenchCompanyName;
public StockName(String symbol, String companyName,
String frenchCompanyName) {
...
}
...
public void formatTo(Formatter fmt, int f, int width, int precision) {
StringBuilder sb = new StringBuilder();
// decide form of name
String name = companyName;
if (fmt.locale().equals(Locale.FRANCE))
name = frenchCompanyName;
boolean alternate = (f & ALTERNATE) == ALTERNATE;
boolean usesymbol = alternate || (precision != -1 && precision < 10);
String out = (usesymbol ? symbol : name);
// apply precision
if (precision == -1 || out.length() < precision) {
// write it all
sb.append(out);
} else {
sb.append(out.substring(0, precision - 1)).append('*');
}
// apply width and justification
int len = sb.length();
if (len < width)
for (int i = 0; i < width - len; i++)
if ((f & LEFT_JUSTIFY) == LEFT_JUSTIFY)
sb.append(' ');
else
sb.insert(0, ' ');
fmt.format(sb.toString());
}
public String toString() {
return String.format("%s - %s", symbol, companyName);
}
}
When used in conjunction with the Formatter, the above
class produces the following output for various format strings.
Formatter fmt = new Formatter();
StockName sn = new StockName("HUGE", "Huge Fruit, Inc.",
"Fruit Titanesque, Inc.");
fmt.format("%s", sn); // -> "Huge Fruit, Inc."
fmt.format("%s", sn.toString()); // -> "HUGE - Huge Fruit, Inc."
fmt.format("%#s", sn); // -> "HUGE"
fmt.format("%-10.8s", sn); // -> "HUGE "
fmt.format("%.12s", sn); // -> "Huge Fruit,*"
fmt.format(Locale.FRANCE, "%25s", sn); // -> " Fruit Titanesque, Inc."
Formattables are not necessarily safe for multithreaded access. Thread
safety is optional and may be enforced by classes that extend and implement
this interface.
Unless otherwise specified, passing a null argument to
any method in this interface will cause a NullPointerException to be thrown.
Public Methods
Formats the object using the provided formatter.
Parameters
| formatter |
The formatter. Implementing classes may call
formatter.out() or formatter.locale() to obtain the Appendable or Locale used by this
formatter respectively. |
| flags |
The flags modify the output format. The value is interpreted as
a bitmask. Any combination of the following flags may be set:
FormattableFlags.LEFT_JUSTIFY, FormattableFlags.UPPERCASE, and FormattableFlags.ALTERNATE. If no flags are set, the default
formatting of the implementing class will apply. |
| width |
The minimum number of characters to be written to the output.
If the length of the converted value is less than the
width then the output will be padded by
' ' until the total number of characters
equals width. The padding is at the beginning by default. If
the FormattableFlags.LEFT_JUSTIFY flag is set then the
padding will be at the end. If width is -1
then there is no minimum. |
| precision |
The maximum number of characters to be written to the output.
The precision is applied before the width, thus the output will
be truncated to precision characters even if the
width is greater than the precision. If
precision is -1 then there is no explicit
limit on the number of characters. |
Throws
| IllegalFormatException |
If any of the parameters are invalid. For specification of all
possible formatting errors, see the Details section of the
formatter class specification.
|
Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.
Last updated 2024-07-10 UTC.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2024-07-10 UTC."],[[["\u003cp\u003eThe \u003ccode\u003eFormattable\u003c/code\u003e interface enables custom formatting for objects using the 's' conversion specifier with the \u003ccode\u003eFormatter\u003c/code\u003e class.\u003c/p\u003e\n"],["\u003cp\u003eIt provides control over formatting through flags, width, and precision parameters within the \u003ccode\u003eformatTo\u003c/code\u003e method.\u003c/p\u003e\n"],["\u003cp\u003eImplementing classes can define how objects are represented based on locale and formatting options.\u003c/p\u003e\n"],["\u003cp\u003eThread safety is not guaranteed and is the responsibility of implementing classes.\u003c/p\u003e\n"]]],["The `Formattable` interface enables custom formatting for objects using the `Formatter` class and its 's' specifier. Classes implementing `Formattable` define how they are formatted via the `formatTo` method. This method takes a `Formatter`, flags (like `LEFT_JUSTIFY` or `ALTERNATE`), width, and precision. It allows control over output length, justification, and alternate forms. The `StockName` class is demonstrated as an example. `formatTo` outputs a formatted string based on locale, flags, and length constraints by calling the `formatter` which in turn calls the object's `toString()` if needed.\n"],null,["# Formattable\n\npublic interface **Formattable** \nThe Formattable interface must be implemented by any class that\nneeds to perform custom formatting using the 's' conversion\nspecifier of [Formatter](../../../reference/java/util/Formatter.html). This interface allows basic\ncontrol for formatting arbitrary objects.\n\nFor example, the following class prints out different representations of a\nstock's name depending on the flags and length constraints:\n\n`import java.nio.CharBuffer;\nimport java.util.Formatter;\nimport java.util.Formattable;\nimport java.util.Locale;\nimport static java.util.FormattableFlags.*;\n\n...\n\npublic class StockName implements Formattable {\nprivate String symbol, companyName, frenchCompanyName;\npublic StockName(String symbol, String companyName,\nString frenchCompanyName) {\n...\n}\n\n...\n\npublic void formatTo(Formatter fmt, int f, int width, int precision) {\nStringBuilder sb = new StringBuilder();\n\n// decide form of name\nString name = companyName;\nif (fmt.locale().equals(Locale.FRANCE))\nname = frenchCompanyName;\nboolean alternate = (f & ALTERNATE) == ALTERNATE;\nboolean usesymbol = alternate || (precision != -1 && precision \u003c 10);\nString out = (usesymbol ? symbol : name);\n\n// apply precision\nif (precision == -1 || out.length() \u003c precision) {\n// write it all\nsb.append(out);\n} else {\nsb.append(out.substring(0, precision - 1)).append('*');\n}\n\n// apply width and justification\nint len = sb.length();\nif (len \u003c width)\nfor (int i = 0; i \u003c width - len; i++)\nif ((f & LEFT_JUSTIFY) == LEFT_JUSTIFY)\nsb.append(' ');\nelse\nsb.insert(0, ' ');\n\nfmt.format(sb.toString());\n}\n\npublic String toString() {\nreturn String.format(\"%s - %s\", symbol, companyName);\n}\n}\n`\n\nWhen used in conjunction with the [Formatter](../../../reference/java/util/Formatter.html), the above\nclass produces the following output for various format strings.\n\n`Formatter fmt = new Formatter();\nStockName sn = new StockName(\"HUGE\", \"Huge Fruit, Inc.\",\n\"Fruit Titanesque, Inc.\");\nfmt.format(\"%s\", sn); // -\u003e \"Huge Fruit, Inc.\"\nfmt.format(\"%s\", sn.toString()); // -\u003e \"HUGE - Huge Fruit, Inc.\"\nfmt.format(\"%#s\", sn); // -\u003e \"HUGE\"\nfmt.format(\"%-10.8s\", sn); // -\u003e \"HUGE \"\nfmt.format(\"%.12s\", sn); // -\u003e \"Huge Fruit,*\"\nfmt.format(Locale.FRANCE, \"%25s\", sn); // -\u003e \" Fruit Titanesque, Inc.\"\n`\n\nFormattables are not necessarily safe for multithreaded access. Thread\nsafety is optional and may be enforced by classes that extend and implement\nthis interface.\n\nUnless otherwise specified, passing a null argument to\nany method in this interface will cause a [NullPointerException](../../../reference/java/lang/NullPointerException.html) to be thrown. \n\n### Public Method Summary\n\n|---------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|\n| abstract void | [formatTo](../../../reference/java/util/Formattable.html#formatTo(java.util.Formatter,%20int,%20int,%20int))([Formatter](../../../reference/java/util/Formatter.html) formatter, int flags, int width, int precision) Formats the object using the provided [formatter](../../../reference/java/util/Formatter.html). |\n\nPublic Methods\n--------------\n\n#### public abstract void\n**formatTo**\n([Formatter](../../../reference/java/util/Formatter.html) formatter, int flags, int width, int precision)\n\nFormats the object using the provided [formatter](../../../reference/java/util/Formatter.html). \n\n##### Parameters\n\n| formatter | The [formatter](../../../reference/java/util/Formatter.html). Implementing classes may call [formatter.out()](../../../reference/java/util/Formatter.html#out()) or [formatter.locale()](../../../reference/java/util/Formatter.html#locale()) to obtain the [Appendable](../../../reference/java/lang/Appendable.html) or [Locale](../../../reference/java/util/Locale.html) used by this formatter respectively. |\n| flags | The flags modify the output format. The value is interpreted as a bitmask. Any combination of the following flags may be set: [FormattableFlags.LEFT_JUSTIFY](../../../reference/java/util/FormattableFlags.html#LEFT_JUSTIFY), [FormattableFlags.UPPERCASE](../../../reference/java/util/FormattableFlags.html#UPPERCASE), and [FormattableFlags.ALTERNATE](../../../reference/java/util/FormattableFlags.html#ALTERNATE). If no flags are set, the default formatting of the implementing class will apply. |\n| width | The minimum number of characters to be written to the output. If the length of the converted value is less than the width then the output will be padded by ' ' until the total number of characters equals width. The padding is at the beginning by default. If the [FormattableFlags.LEFT_JUSTIFY](../../../reference/java/util/FormattableFlags.html#LEFT_JUSTIFY) flag is set then the padding will be at the end. If width is -1 then there is no minimum. |\n| precision | The maximum number of characters to be written to the output. The precision is applied before the width, thus the output will be truncated to precision characters even if the width is greater than the precision. If precision is -1 then there is no explicit limit on the number of characters. |\n|-----------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|\n\n##### Throws\n\n| [IllegalFormatException](../../../reference/java/util/IllegalFormatException.html) | If any of the parameters are invalid. For specification of all possible formatting errors, see the [Details](../util/Formatter.html#detail) section of the formatter class specification. |\n|------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|"]]
