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 Method Summary
| abstract void |
Public Methods
public abstract void formatTo (Formatter formatter, int flags, int width, int precision)
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. |
|---|