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package java.util;
import java.io.IOException;
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.
Since: 1.5
/**
* The {@code Formattable} interface must be implemented by any class that
* needs to perform custom formatting using the {@code 's'} conversion
* specifier of {@link java.util.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:
*
* <pre> {@code
* 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);
* }
* }
* }</pre>
*
* <p> When used in conjunction with the {@link java.util.Formatter}, the above
* class produces the following output for various format strings.
*
* <pre> {@code
* 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."
* }</pre>
*
* <p> Formattables are not necessarily safe for multithreaded access. Thread
* safety is optional and may be enforced by classes that extend and implement
* this interface.
*
* <p> Unless otherwise specified, passing a {@code null} argument to
* any method in this interface will cause a {@link
* NullPointerException} to be thrown.
*
* @since 1.5
*/
public interface Formattable {
Formats the object using the provided formatter. Params: - 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.
/**
* Formats the object using the provided {@link Formatter formatter}.
*
* @param formatter
* The {@link Formatter formatter}. Implementing classes may call
* {@link Formatter#out() formatter.out()} or {@link
* Formatter#locale() formatter.locale()} to obtain the {@link
* Appendable} or {@link Locale} used by this
* {@code formatter} respectively.
*
* @param flags
* The flags modify the output format. The value is interpreted as
* a bitmask. Any combination of the following flags may be set:
* {@link FormattableFlags#LEFT_JUSTIFY}, {@link
* FormattableFlags#UPPERCASE}, and {@link
* FormattableFlags#ALTERNATE}. If no flags are set, the default
* formatting of the implementing class will apply.
*
* @param width
* The minimum number of characters to be written to the output.
* If the length of the converted value is less than the
* {@code width} then the output will be padded by
* <code>' '</code> until the total number of characters
* equals width. The padding is at the beginning by default. If
* the {@link FormattableFlags#LEFT_JUSTIFY} flag is set then the
* padding will be at the end. If {@code width} is {@code -1}
* then there is no minimum.
*
* @param 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 {@code precision} characters even if the
* {@code width} is greater than the {@code precision}. If
* {@code precision} is {@code -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 <a
* href="../util/Formatter.html#detail">Details</a> section of the
* formatter class specification.
*/
void formatTo(Formatter formatter, int flags, int width, int precision);
}